EVALUATION OF F4 GENERATION OF COWPEA (VIGNA UNGUICULATA) GENOTYPES FOR DROUGHT TOLERANCE AND HIGH YIELD BY ATSORIBO NICHOLSON EBEN (10562732) THIS THESIS IS SUBMITTED TO THE UNIVERSITY OF GHANA, LEGON IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF PHILOSOPHY DEGREE IN CROP SCIENCE UNIVERSITY OF GHANA COLLEGE OF BASIC AND APPLIED SCIENCES DEPARTMENT OF CROP SCIENCE DECEMBER,2022 University of Ghana http://ugspace.ug.edu.gh University of Ghana http://ugspace.ug.edu.gh i DECLARATION Date: 13/11/2023 Date: 13/11/2023 Date: 13/11/2023 University of Ghana http://ugspace.ug.edu.gh ii ABSTRACT Globally, demand for improved agricultural production has increased as a result of an increasing human population. Drought and heat stress brought on by climate change exacerbate the difficulties of increasing crop production. Drought stress has a primary consequence of lowering crop output by reducing biomass and seed weight. Irrigation and breeding are two strategies for minimizing the consequence of drought or addressing the problem of drought stress. Irrigation, on the other hand, necessitates a significant upfront investment and the availability of water throughout the growing season, particularly during flowering and pod filling. This makes it more difficult, particularly for African small-scale farmers. The study was aimed at increasing cowpea yield through improved tolerance to drought. There was high diversity among the genotypes for days to first flowers, chlorophyll content, plant healthiness, stem greenness, number of seeds per pod, number of pods per plant, number of days to maturity, and ultimately the yield of the genotypes across all the treatments applied. The most decline was observed in the pod filling stage drought treatments across all measured parameters. Pearson correlation was conducted to observe the relationships between the parameters measured. The correlation analysis revealed a strong relationship was established between chlorophyll content and plant healthiness. Number of pods per plant was positively correlated to number of seeds per pod and similarly, seed size and pod length, revealing that the size of seeds and number of seeds in a pod determines the length of the pod. The ranking of genotypes based on the three drought tolerant parameters revealed some genotypes that performed better than Danila, a known drought tolerant line and Hewale the high yielding local cultivar. High yielding and drought tolerant genotypes for the vegetative and pod filling stage drought showed true drought tolerance. University of Ghana http://ugspace.ug.edu.gh iii DEDICATION I dedicate this thesis to God Almighty and also to my cherished parents. University of Ghana http://ugspace.ug.edu.gh iv ACKNOWLEDGEMENT My grateful to the many who in diverse ways contributed to this work. My sincerest gratitude goes to Dr. John Eleblu and Prof. Kwadwo Ofori for their guidance and support. I thank the management and staff of the west Africa Centre for Crop Improvement (WACCI) University of Ghana for funding the project as well as to the UG-Tullow scholarship scheme. Special thanks to Portia Mensah, Seth Arthur, Godslove Narh and Salaudeen Bandanaa for their commitment and hard work on the field. University of Ghana http://ugspace.ug.edu.gh v TABLE OF CONTENTS DECLARATION............................................................................................................................ i ABSTRACT ................................................................................................................................... ii DEDICATION.............................................................................................................................. iii ACKNOWLEDGEMENT ........................................................................................................... iv TABLE OF CONTENTS ............................................................................................................. v LIST OF TABLES ...................................................................................................................... vii LIST OF FIGURES ................................................................................................................... viii LIST OF ABBREVIATIONS ..................................................................................................... ix CHAPTER 1 ................................................................................................................................ 11 1.0 INTRODUCTION............................................................................................................. 11 1.1 Main Objective of the study ......................................................................................... 17 CHAPTER TWO ........................................................................................................................ 18 2.0 LITERATURE REVIEW ................................................................................................ 18 2.1 Cowpea taxonomy, origin, domestication ................................................................... 18 2.2 Cultivation and utilization of cowpea in Africa ......................................................... 20 2.3 World Cowpea Production........................................................................................... 21 2.4 Constraints to Cowpea Production ............................................................................. 23 2.5 Effect of drought on agriculture and food security ................................................... 24 2.6 EFFECTS OF DROUGHT ON COWPEA ................................................................ 25 2.7 UNDERSTANDING DROUGHT: METEOROLOGICAL, AGRICULTURAL, HYDROLOGICAL AND SOCIOECONOMIC DROUGHT ............................................. 27 2.8 Drought coping Mechanisms in plants ........................................................................ 29 2.8.2 Drought Avoidance in Cowpea ................................................................................. 31 2.10 Genetics of drought tolerance .................................................................................... 37 3.0 MATERIALS AND METHODS ................................................................................ 39 3.1 Experimental Site .......................................................................................................... 39 3.2 Planting Material .......................................................................................................... 39 3.8 Harvesting and Storage ................................................................................................ 41 3.9 Drought Stress Treatment and Experimental design ................................................ 41 3.11 Data collection ............................................................................................................. 41 University of Ghana http://ugspace.ug.edu.gh vi 3.12 DATA ANALYSIS ...................................................................................................... 44 CHAPTER FOUR ....................................................................................................................... 46 4.0 RESULTS .......................................................................................................................... 46 4.1 Chlorophyll content for different stages of drought treatment. ............................... 46 4.2 Overall Plant Healthiness ............................................................................................. 48 4.3 STEM GREENESS ....................................................................................................... 50 4.4 CORRELATION ANALYSIS OF DROUGHT TOLERANCE TRAITS. .............. 52 4.5. Factor analysis of traits towards observed variability. ........................................... 54 4.6 CORRELATION ANALYSIS OF YIELD AND YIELD RELATED TRAITS ..... 56 4.7 GENETIC VARIABILITY OF YIELD AND YIELD RELATED ATTRIBUTES 58 4.8 EFFECT OF WATER STRESS ON THE DAYS TO FIRST FLOWERING ........ 61 Table 7: Mean number of Days to first flowers for different genotypes under different stress conditions. ................................................................................................................. 62 4.10 EFFECTS OF WATER STRESS ON POD LENGTH ........................................... 65 4.11 EFEFECTS OF WATER STRESS ON SEED YIELD ........................................... 67 4.12 EFEFECTS OF WATER STRESS ON SEED SIZE ............................................... 69 4.13 EFFECTS OF WATER STRESS ON DAYS TO MATURITY ............................. 71 CHAPTER 5 ................................................................................................................................ 73 5.0 DISCUSION ...................................................................................................................... 73 5.1 Three drought-tolerance parameters. ......................................................................... 73 5.2 SEED SIZE .................................................................................................................... 75 5.3 DAYS TO FIRST FLOWERS AND MATURITY .................................................... 76 5.4 MEAN YIELD AND YIELD COMPONENTS OF THE COWPEA GENOTYPES ............................................................................................................................................... 76 5.5 Relationship Between Yield and Yield Components ................................................. 79 CHAPTER 6 ................................................................................................................................ 83 6.0 CONCLUSIONS AND RECOMMENDATIONS .......................................................... 83 6.1 CONCLUSIONS ........................................................................................................... 83 6.2 Recommendations ......................................................................................................... 84 References .................................................................................................................................... 85 Appendices ................................................................................................................................. 112 University of Ghana http://ugspace.ug.edu.gh vii LIST OF TABLES Table 1: Characteristics of cowpea varieties used for the study…………………………………29 Table 2. Correlation analysis of Chlorophyll decrease, stem lodging increase and healthiness change…53 Table 3. Factor analysis based on yield and yield related attributes of cowpea F4 population ……………………………………………………………………………………………………55 Table 4 Correlation analysis of yield and yield related parameter……………………………………57 Table 5. Genetic parameters of variability for cowpea F4 population………………………………59 Table 6: Mean number of Days to first flowers for different genotypes under different stress conditions………………………………………………………………………………….……..62 Table 7: Mean number of Seeds per pod for different genotypes under different stress conditions………………………………………………………………………………………...64 Table 8: Mean number pod length for different genotypes under different stress conditions……66 Table 9: Mean seed yield for different genotypes under different stress conditions…………….68 Table10: Mean seed size for different genotypes under different stress conditions………………70 Table 11: Mean number of days to maturity different genotypes under different stress conditions…………………………………………………………………………………………….67 University of Ghana http://ugspace.ug.edu.gh viii LIST OF FIGURES Figure 1: Share of Africa in world cowpea production………………………………………….12 Figure 2. Chlorophyll content change of cowpea plant………………………………………….35 Figure 3. Healthiness change of cowpea plant…………………………………………………...41 Figure 4. Greenness change of cowpea plant ……………………………………………………47 University of Ghana http://ugspace.ug.edu.gh ix LIST OF ABBREVIATIONS AFLPs Amplified Fragment Length Polymorphisms CABMV Cowpea Aphid Borne Mosaic CII Chlorophyll Inflect Index CMV Cucumber Mosaic Virus CPMMV Cowpea Moderate Mottle Virus DAS Days After Sowing DMRT Duncan’s Multiple Range Test FAO Food And Agricultural Organization of The United Nations GCA General Combining Ability GDP Gross Domestic Product HII Healthiness Inflect Index IITA International Institute of Tropical Agriculture MAS Marker-Assisted Selection MoFA Ministry Of Food and Agriculture PF Pod Filling Stage PUFA Polyunsaturated Fatty Acids QTL Quantitative Trait Loci RAPDs Random Amplified Polymorphic DNAs RCBD Randomized Complete Block Design RFLPs Restriction Fragment Length Polymorphisms RuBP Ribulose-1,5-Bisphosphate University of Ghana http://ugspace.ug.edu.gh x SARI Savannah Agricultural Research Institute SCA Specific Combining Ability SSA Sub-Saharan Africa SSRs Simple Sequence Repeats UNCCD United Nations Convention to Combat Desertification VEG Vegetative Stage VP Vegetative And Pod Filling Stage WACCI West Africa Centre for Crop Improvement WCA West And Central Africa University of Ghana http://ugspace.ug.edu.gh 11 CHAPTER 1 1.0 INTRODUCTION Cowpea (Vigna unguiculata (L.) Walp) is a significant legume crop that is grown extensively in arid and semi-arid agroecologies around the world under low input production techniques. It belongs to the family Fabaceae and sub-family Faboideae(Horn & Shimelis, 2020). It is a vital crop for Africa. It holds a high quantity of protein (19 to 35%)(Horn & Shimelis, 2020), 64% carbohydrates, and significant amounts of fiber, minerals, and vitamins (Yahaya et al., 2019a). Cowpea is a vital element of the diet of many individuals in Africa and other underdeveloped countries, where it provides a key source of protein. It is a healthfully advantageous dietary protein source and compliments low protein staple cereals and tuber crops. It is also a reliable and valuable resource that generates revenue for farmers and merchants (Timko et al.,2007; Singh et al., 2007; Langyintuo et al., 2003). In addition to nutrients, cowpea contains dietary fibre, antioxidants, polyunsaturated fatty acids (PUFA), and polyphenols (Nkomo et al., 2021a) with the grains also high in lysine and tryptophan, two important amino acids (Horn & Shimelis, 2020). It is mainly a self-fertilizing crop. Cowpea is a crop that has the ability to fix nitrogen in the soil, restoring soil fertility. Farming households profit financially from the sale of the grains, leaves, or fodder as well as food processing by-products (Yahaya et al., 2019b). The crop is known as a hunger crop because it matures early, allowing the edible leaves to be used during a time of year when food stores from earlier harvests have been depleted and newly planted seeds of other agricultural crops are not yet available for harvest (Yahaya et al., 2019a). As a plant-based diet, it boosts fiber consumption, which lowers the risk of bowel disorders, including cancer, as well as the incidence of osteoporosis (Khalid & Elhardallou, 2016). With the exception of Nigeria, which yearly produces the most University of Ghana http://ugspace.ug.edu.gh 12 cowpea grains (3.57 million metric tonnes), the United States, Peru, Serbia, Sri Lanka, and China were all named as the top producers throughout the previous three years(2014-2016) (FAOSTAT, 2017). Cowpea is cultivated on around 14.5 million hectares worldwide, yielding roughly 8.9 million metric tons per year (FAOSTAT, 2019). West Africa Is the largest producer of cowpeas in Sub-Saharan Africa (SSA), with 80% of the region's entire production over the previous 14 years being produced by Nigeria and Niger (Boukar et al., 2018). Cowpea is an important crop in Ghana because of its impact on the country's GDP, household earnings, and food and nutritional security. In terms of consumption, cowpea comes second after peanuts (Egbadzor, 2013; MOFA/SRID, 2011), and it is crucial for the economy and diet of urban and rural poor (SARI, 2014). Cowpea production is predominant in five regions of Ghana, namely, Northern, Upper West, Upper East, Brong Ahafo, and Ashanti regions (MOFA, 2016). The northern parts of Ghana are the major producers of cowpea. Although there is seasonal variation in rainfall, the main cowpea producing region is characterized by the unpredictable nature of this change. Cowpea has a short crop cycle and integrates well into cropping niches where other crops do not. In particular, cowpea production is gaining prominence in the hydromorphic lowlands between April and June before rice is produced. In the northern Savanna zones of West Africa, average farm level yields of cowpea are still within 0.8 t/ha on farmers’ fields even though varieties with grain yield potentials are in excess of 3.0 tonnes per hectare (t/ha) have been developed for such ecologies (SARI, 2014). Because of its multiple advantages, cowpea is practically cultivated by all smallholder farmers in most of Ghana's agro-ecological zones. Unfortunately, the complex nature of the abiotic and biotic stress usually leads to low grain yield of cowpea. According to MOFA (2016), typical yields in farmer's fields in Ghana range between 400 and 600 kg/ha, equated to potential yields of 1600 to 2500 kg/ha in research fields. The usage of unimproved local cultivars, poor soil fertility, drought, and University of Ghana http://ugspace.ug.edu.gh 13 other biotic and abiotic stressors are all linked to low yield. The reduced potential yield of cowpeas in sub-Saharan Africa is caused by a number of biotic and abiotic causes, including insect pests, diseases (fungal, viral, and bacterial), inadequate soil fertility, metal toxicity, and drought (Sala et al., 2008; Boukar et al., 2018; Gomes et al., 2019.). A plant may become tolerant to drought by a variety of methods, including drought escape, drought avoidance, or drought tolerance. Plants might employ a combination of mechanisms for dealing with drought (Ludlow, 1989; Mitra, 2001; Yue et al., 2006). The capacity of a plant to finish its life cycle prior to the commencement of a severe water deficit is known as drought escape. (Yue et al., 2006; Bhatnagar-Mathur et al., 2010). This mechanism comprises speedy phenological growth (early flowering, early podding and early maturity) (Gaur et al., 2008). Despite the fact that studies have shown there is a production penalty for any crop maturity time reduction below the ideal (Caliskan et al., 2008), a prominent approach in breeding crops for drought tolerance is the choice of earliness. This is because, early cultivars offer immediate income at the start of the cropping seasons, is produced in varied cropping systems and can escape some insect infestation (Ehlers and Hall, 1997). Drought avoidance is the ability of plants to maintain a high-water status or cellular hydration while experiencing the impacts of drought (Blum, 2005). Plants use this method to reduce water loss by closing their stomata and increasing lenticular conductivity (Chaves et al., 2003), limiting absorption of solar radiation by leaf rolling or folding/Para heliotropism (Fatokun et al., 2012) and decreasing the area of the leaf where water is lost through evaporation, as well as creating a thick trichome layer that improves reflectivity (Yue et al., 2006; Taiz and Zeiger, 2006). They boost the roots’ systems ability to take up water (Jackson et al., 2000) and root traits including thickness, depth, length, and density, for example in rice (Ekanayake et al., 1985). This mechanism affects how efficiently water is used as well as how evapotranspiration is controlled. The capacity of plants to survive water shortages University of Ghana http://ugspace.ug.edu.gh 14 with low tissue water potential is known as drought tolerance. The approach includes the creation of various stress-relieving substances, the preservation of turgor via osmotic adjustment (concentration of solutes in the cell), enhanced cell flexibility and reduced cell size, and desiccation tolerance via protoplasmic resistance (Agbicodo et al., 2010). It deals with the recovery and survival of genotypes following a protracted and severe internal water deprivation. In the event of a 95% loss of leaf water, these genotypes can still exist (Scott et al., 2000). Dehydration tolerance allows plants to withstand lengthy and difficult water deficits and recover when it rains. Additionally, it enables plants to extend the duration of their metabolic processes and transfer assimilates to the storage tissues (Fukai and Cooper, 1995). Plants escape dehydration as a result of biochemical mechanisms that entail the build-up of compatible solutes, primarily nitrogen molecules (McCue and Hanson, 1990). These antioxidants and solutes are present in plants in various forms and concentrations. These solutes collaborate with antioxidants, which function to reduce reactive oxygen species (ROS), safeguard cellular components by osmotic adjustment, and maintain the proper balance between the creation and destruction of free radicals (McCue and Hanson, 1990; Lin et al., 2006; Brosché et al., 2010). By displaying delayed leaf senescence (DLSC), which is comparable to the stay-green traits in cereals, the cowpea exhibits a tolerance mechanism (Gwathmey and Hall 1992; Hall et al., 1997). According to research, cowpea plants with the delayed leaf senescence( DLSC)trait were capable of surviving the mid-season drought brought on by sporadic rains and produce a second flush of pods for an increase in grain output (Hall et al., 2003). It is possible for there to be a drought at the start of the growth season, when rain stops soon after planting, or in the middle of the season, just before the plants flower, or from the reproductive to the pod-filling stage. Early maturity is a strategy for escaping drought, however drought tolerance at the seedling stage and DLSC will increase the plants' capacity to endure University of Ghana http://ugspace.ug.edu.gh 15 drought during the early and mid-season as well as the pod filling stages. For sorghum, it has been reported that genotypes with DLSC (stay green) can maintain physiological activity during the latter phases of grain filling in conditions of terminal drought (van Oosterom et al., 1996). Globally, demand for improved agricultural production has increased as a result of an increasing human population (Lesk et al., 2016). Drought and heat stress brought on by climate change exacerbate the difficulties of increasing crop production (Fahad et al., 2017). Droughts, both terminal and intermittent, reduce crop yields significantly because of their detrimental effects on plant development, physiology, and reproduction (Barnabás et al., 2008). Drought stress has a primary consequence of lowering crop output by reducing biomass and seed weight (Dellal & McCarl, 2010). Irrigation and breeding are two strategies for minimizing the consequence of drought. Irrigation, on the other hand, necessitates a significant upfront investment and water supply for the entire planting season, particularly during flowering and pod filling. Due to this, it is harder, particularly for African small-scale farmers. As a result, genotypes that can withstand water stress should be selected. Developing drought-tolerant cultivars is a more long-term solution to drought management because farmers will not incur any additional charges once drought- tolerant seeds are accessible. Drought tolerance and grain yield, on the other hand, are complicated to breed since they are governed by minor genes whose impacts are usually confounded by interactions between the crop's morphological, physiological, and biochemical features and the environment, making genetic enhancement of these traits in crops a lengthy a challenging procedure(Fatokun et al., 2012; Mir et al., 2012). Tsamenyi (2018), in evaluating F2 populations of cowpea showed some genotypes with drought tolerance potential. Ngalamu et al., (2019) also University of Ghana http://ugspace.ug.edu.gh 16 identified some genotypes with stability for drought tolerance and high grain yield. Drought tolerance is polygenic, making it difficult to find tolerant genotypes in drought-prone areas (Ngalamu et al., (2019). The goal of breeding programs is to create cultivars that outperform previously available cultivars(Daniele Lustosa Silva Jéssica DA et al., 2017). However, getting access to cultivars with these advantages is possible if the new cultivar simultaneously has several phenotypes of interest, such as high grain yield and quality, a plant growth habit that allows for mechanization, high pest and disease resistance, tolerance to high temperatures and water stress, good nutritional quality, high production stability, and adaptation to different environments(Daniele Lustosa Silva Jéssica DA et al., 2017). The failure of a cultivar can be caused by the identification of superior genotypes based on only one attribute, especially when economic and commercial characteristics, as well as customer preferences, are ignored (Cruz et al., 2004). Selection is a crucial phase in genetic improvement that must be carried out with extreme caution. As a result, due to the difficulty of simultaneous selection, selection indices are utilized as a substitute for identifying superior genotypes for various features. Low heritability, polygenic control, epistasis, considerable genotype by environment (G x E) and quantitative trait loci (QTL) by environment (QTL x E) interactions have all hindered straight selection for grain yield under water-stress conditions (Piepho, 2000). The delayed progress in yield enhancement in drought-prone regions can be attributed to the complexity of drought tolerance mechanisms. Cowpea cultivars with improved drought and heat tolerance, as well as high biological nitrogen fixation, have been identified by researchers and plant breeders (Singh, 2014). Estimating the genetic gain can be used to quantify the increase in a population's average performance after each selection cycle due to an increase in the frequency of beneficial alleles. The calculation of genetic gain helps breeders to University of Ghana http://ugspace.ug.edu.gh 17 assess the efficacy of their breeding strategies and direct them toward the formation of superior populations (Cruz et al, 2004; FERH, 1987). 1.1 Main Objective of the study The main objective of the study was to increase cowpea yield through improved tolerance to drought. Specific objectives The specific objectives of the study were to; 1. identify drought tolerant lines among F4 cowpea populations, 2. Evaluate selected F4 cowpea drought tolerant lines for high yield and sub-yield components 3. identify drought tolerant lines with combined drought tolerance and high grain yield. University of Ghana http://ugspace.ug.edu.gh 18 CHAPTER TWO 2.0 LITERATURE REVIEW 2.1 Cowpea taxonomy, origin, domestication Cowpea [Vigna unguiculata (L.) Walp.] was originally named for the fact that it was used as hay to feed cows in some parts of the world, such as the southeastern United States (Timko et al., 2007). It is a diploid (2n = 2x = 22) whose genome size is over 620Mb (Timko and Singh, 2008), and is one of the oldest human food sources with evidence of its use as a crop plant dating back to the Neolithic period (Summerfield et al., 1974). It belongs to Fabaceae family (Jayathilake et al.,2018) and sub-family Faboideae (Agbogidi, 2010). Sharma et al., (2016), states that all cowpeas grown, are included under the species Vigna unguiculata, that is also categorized into four cultivar groups: Unguiculata (common cowpea for food and fodder), Biflora (catjang), Sesquipedalis (yard long or asparagus bean used as a vegetable), and Textilis (used for fibres). Unguiculata is the most diversified amongst the cultivar groups, and it is extensively farmed in Africa, Asia, and Latin America (Fang et al., 2007). The only cultivated cowpea is subspecies unguiculata, while the other three are wild relatives. It's tough to pinpoint where a species' center of origin actually is (B. B. Singh et al., 1997). Botanical and cytological evidence, information on geographical dispersion, along with cultural practices and historical records, have been referenced to make assumptions of the genesis and naturalization of cowpea [Vigna unguiculata (L.) Walp.] (Ng, 1995). According to Huynh et al., (2013), cowpea was first transported from West Africa with African people at the time of the slave trade to other parts of the globe. However, there were s no documents to back the extent of University of Ghana http://ugspace.ug.edu.gh 19 movement extent. Cowpea is thought to have originated in West Africa by other scholars, while the specific site of the species' origin is unknown. A thorough examination of a crop's physical and genetic variation in connection to its geographical distribution could aid in speculating on the origin of cultivated plants(B. B. Singh et al., 1997). Huynh et al., (2013) utilized SNP makers to investigate the gene pool structure of the African wild annual cowpea V. unguiculata subsp. dekindtiana from East and West Africa, as well as their kinship to African wild cowpeas and non- African domesticated cowpeas. Two gene pools were created from the genetic material., according to these researchers. The two gene pools were dispersed across two main geographic regions, which were divided by the vast and dense Congo River basin rainforests according to Batieno (2016) in a related study. Cowpea remnants were unearthed in Ghana's Kintampo and carbon dated to around 1400-1480 BC, making it the earliest archaeological confirmation of this crop (Flight, 1976). Due to the existence of the most primitive wild varieties, var. rhomboidea, var. protracta, var. tenuis, and var. stenophylla, the Transvaal region of the Republic of South Africa was most likely the focus of V. unguiculata diversification(B. B. Singh et al., 1997). By 2000 BC, the West African collection reached India, as revealed in a study carried out using more than 10,000 accessions from the global collection at the International Institute of Tropical Agriculture's (IITA) (Padulosi and Ng, 1997). The Greeks and Romans brought it to Europe, and called it Phaseolus. It was very recently made known to the Americas. IITA's research revealed that West African germplasm were more diverse than East African germplasm (Padulosi and Ng, 1997). These discoveries added to the growing body of evidence indicating West Africa was the principal breeding ground for domesticated animals. The Savanna regions of Nigeria, southern Benin, Togo, and the north-western section of Cameroon are home to the greatest diversity of University of Ghana http://ugspace.ug.edu.gh 20 farmed cowpeas (Ng and Marechal, 1985). According to Verdcourt (1970), Vigna has multiple species, however the precise number differs depending on the author. 2.2 Cultivation and utilization of cowpea in Africa Legume crops play an essential role in agricultural sustainability, household income, and nutritional systems. Cowpea is grown across Africa, and in portions of Southeast Asia and Latin America. Cowpea is currently farmed in the tropics and subtropics all over the world within a latitudinal range of 350N and 300S of the equator, with low rainfall (300-600 mm) (Fatokun et al., 2012). Sub-Saharan Africa, Asia, South America, Central America, the Caribbean, Oceania, South of the United States of America, and the Mediterranean Sea region are all part of this zone where cowpea is grown (Padulosi and Ng, 1997; OECD, 2015; Onuh and Donald, 2009). It is mostly a warm-weather crop(Alidu, 2019) that is more suited to drought, high temperatures, and other biotic stresses compared to most other crops (Onuh and Donald,2009). It is grown primarily for its seeds, which have high protein (20–32%), carbohydrate (50–60%) (Gomes et al., 2020) and dry matter content and is mostly eaten as a dry grain or as a raw vegetable. The grain which has a high protein content is also high in lysine and tryptophan which are two important amino acids (Abadassi,2015). Cowpea is thus an important part of the human diet in many poorer nations, earning it the nickname "poor man's meat. (Jayathilake et al., 2018). Because rhizobium facilitates the fixing of atmospheric nitrogen, contributing to soil fertility enhancement in leguminous plants, cowpea has become a key component of traditional cropping systems as a legume, notably in farming systems used by smallholder farmers where little or no fertilizer is used (Bado et al., 2006) and many of these smallholder farmers in Africa and the developing countries depend on it for food, cash, animal feed, and fertiliser (Menssena et al., 2017). Cowpea is the most valuable native University of Ghana http://ugspace.ug.edu.gh 21 African legume crop, with diverse applications as a nutrient-dense component of human and cattle diets (Langyintuo et al., 2003). Because it is frequently harvested prior to maturity of the cereal crops, it is called a "hungry-season crop." Cowpea grain has a high protein content, which makes it ideal for use in new born and children's meals (Agyeman et al., 2014). It also has a low-fat content, which is beneficial in preventing a variety of metabolic and cardiovascular illnesses(Gonçalves et al., 2016). The mature pods are picked, and the haulms are chopped and rolled into little bundles with the leaves and vines while still green(Agbicodo, 2009). Cowpea haulms can bring up to 50% of the grain price (dry weight basis). Over 70% of Ghana’s population depend on it as their source of minerals and vegetable protein. The season for cowpeas in Ghana varies depending on the types the farmer wishes to sow and their goals. The major rainy season (May) and the minor rainy season (August) are the two main seasons in Ghana, but the crop can be planted at any time throughout the major season. When used as cattle fodder, the crop can be intercropped with some cereal crops (MoFA, 2002). The majority of Ghanaian cowpea is grown in the Sudan savanna, one of Ghana's agro-ecological savanna zones. Cowpea seeds for planting are available in Ghana through market/traders, farmers' stock seeds, and farmers who save seeds for sale (MOFA, 2005). Despite its origins in West Africa, this bean has found its way into the diets of over 110 million people worldwide (Ogbuinya, 1997). 2.3 World Cowpea Production According to FAOSTAT (2020), cowpea was grown on an about 15 million ha worldwide with14.8ha in Africa in 2020 with majority of production limited to West Africa (12.7 million ha), especially in Nigeria, Niger, Burkina Faso, Senegal, Ghana and Mali. A little over 8.9 million tons University of Ghana http://ugspace.ug.edu.gh 22 of cowpeas are produced globally, with Africa generating almost 8.6 million tons. West and Central Africa (WCA) account for more than 64% of the area – 9.2 million hectares followed by roughly 2.4 million hectares in Central and South America, 1.3 million hectares in Asia and about 0.8 million hectares in Eastern and South Africa (Olubunmi, 2015). Nigeria is the largest producer and user of cowpeas and accounts for 46.3% of the production in Africa and 41% globally (FAOSTAT, 2020) as compared to 1% of the production in Africa and 58% Worldwide (Baysah, 2013). 52% of total African production of cowpeas is utilized as food, 13% as animal feed, 10% for seeds, 9% for other uses, and 16% being wasted(Nkomo et al., 2021b). Figure 1: Share of Africa in world cowpea production. Source: FAOSTAT (2020) University of Ghana http://ugspace.ug.edu.gh 23 2.4 Constraints to Cowpea Production Even though for its numerous characteristics, cowpea is among the most popular crops and a vital element in the farming systems of numerous rural SSA households with little access to resources (Molosiwa et al., 2016). Poor yields, ranging from 100 to 599 kg ha-1 compared to expected yields of 1500 to 3000 kg ha-1 have been seen in cowpea. This can be attributed to biotic and abiotic stressors. Insect pests (aphid, flower thrips, maruca, pod sucking bugs, bruchid), diseases (bacterial, fungal, and viral), Striga (S. gesnerioides), and Alectra can cause yield loss ranging from 15% to 100% depending on the extent and intensity of infestation, variety vulnerability/resistance, drought, and low soil fertility. Other obstacles include shortage of inputs such as fertilizers, pesticides, and improved seeds, as well as poor cultural practices and a lack of appropriate technology for expanding cultivated area(Tropical Legume II, 2012). Over 40 species of fungi have been identified as causing disease in cowpea. These fungi cause leave smut, stem rot, and root rot in the plant with losses ranging from 20%-100%. Sources of fungal pathogen resistance have been identified, and screening approaches have been refined (Pujari,2015). There are over 20 viruses reported to have detrimental effects on cowpea productivity globally. In other locations, these viruses have been linked to 90% output reduction or even total crop failure (Mbeyagala et al., 2014). Cowpea aphid borne mosaic (CABMV), cucumber mosaic virus (CMV), cowpea moderate mottle virus (CPMMV), and cowpea severe mosaic virus are the most common viral infections in cowpea, according to Mbeyagala et al., (2014). (CPSMV). In certain years, aphid infestation on cowpea causes a 100% yield loss (Horn et al., 2015). The red mosaic virus inhibits the growth and development of rhizobium bacteria. Root nodulation had decreased by 20 to 45 percent as a result of this (Taiwo et al., 2014). The red mosaic virus stops the expansion and advancement of rhizobium bacteria and as a result, root nodulation is decreased by 20 to 45% University of Ghana http://ugspace.ug.edu.gh 24 (Taiwo et al., 2014). Bacteria pathogens on the other hand, cause yield loses of up to 71%,68% and 53% in pod, seed and fodder of susceptible varieties respectively (Viswanatha et al.,2011). During mild infection, usual signs include a gradual yellowing of the leaves with irregular to circular dots. This causes senescence and leaf drooping(Horn & Shimelis, 2020). The two principal parasitic weeds influencing cowpea production in SSA are Striga gesnerioides (Wild.) Vatke and Alectra vogelii Benth. Weeds spread and attach themselves to the host's root surfaces, where they receive nutrition (Horn et al., 2015). In Ghana, Striga gesnerioides causes significant yield losses in cowpea. Drought stress is the most devasting abiotic stress in cowpea production. Despite the fact that cowpea is mostly grown in arid areas of Sub-Saharan Africa and can tolerate soils with low levels of moisture, drought is still one of the major climatic conditions that determines whether a crop is productive and profitable(Horn & Shimelis, 2020). 2.5 Effect of drought on agriculture and food security The primary means of support for people living in rural areas continues to be agriculture, in Sub- Saharan Africa, giving cash, food, and employment to farmers, as well as contributing to a country's GDP. Climate and weather conditions have a significant impact on agricultural production and productivity. Due to unpredictable rainfall at the start and conclusion of the rainy season, drought has been noted as a serious restriction in semi-arid tropics (Olajide,2017). Drought can strike in the middle of the planting season or near the end, and it has been shown to have a devastating effect on cowpea yield regardless of when it occurs. Cowpea can suffer from both heat and drought stress in West Africa's Sahelian and dry savanna zones with early flowering kinds surviving dryness in select places and years to produce useful grain yields. (Ajayi et al., 2018). Drought is a regular hazard in Ghana's northern region, although the country as a whole is prone University of Ghana http://ugspace.ug.edu.gh 25 to it(UNCCD, 2015). Droughts in Ghana often tend to have parallels in the past within a 30 year or so time frame. However, they have become increasingly common in recent years, as World Bank research (2010) on precipitation forecasting showed a cyclical trend for all parts of the country over the period 2010-50, with high rainfall levels followed by drought every decade or two(UNCCD, 2015). Drought stress affects cowpea at both the seedling and terminal growth phases, reducing grain yield and biomass production significantly(Nkomo et al., 2021b). Droughts can be intermittent, occurring at one or more times during the growth season of the crops, or terminal, resulting in a steady decline in available soil moisture content and severe drought (Ibitoye,2015). Due to a combination of high temperatures, drought, and longer daylengths, floral bud development might be slowed or inhibited, resulting in fewer flowers and poorer cowpea output(Ndiso et al., 2016). Drought stress's effects on crop output can have a considerable negative influence on farmer income and, as a result, on GDP growth (Mou et al., 2018). Drought-related yield losses in agricultural crops have been estimated at 17% (Ashraf et al., 2008). 2.6 EFFECTS OF DROUGHT ON COWPEA Severe or even slight water drought conditions is able to result in some biochemical limitation of photosynthesis in cowpea plants in a genotype-dependent manner. These biochemical limitations include decreases in phosphorylation, ribulose-1,5-bisphosphate (RuBP) regeneration, and Rubisco activity (Rivas et al., 2016; S. K. Singh & Raja Reddy, 2011), damage to the membranes and abnormalities in the functioning of several enzymes, including those involved in CO2 fixation and adenosine triphosphate synthesis (Tetteh et al., 2019). Drought events restrict the performance of cowpea plants at numerous developmental stages and biological processes, ranging from embryo to reproductive and maturity (Kapoor et al., 2020) Despite the fact that cowpea is a drought-tolerant crop(Carvalho et al., 2019; Goufo et al., 2017; Horn & Shimelis, 2020; Mou et University of Ghana http://ugspace.ug.edu.gh 26 al., 2018; Olubunmi, 2015; Timko & Singh, 2008). According to Farooq et al., (2017), cowpea yields can decline from 34% to 68% dependent on the time of drought stress development. Seedling stage drought mostly led to a reduction in plant height owing to reduced turgor, which affects cell division, expansion and elongation, reduction in leaf, stem, root, total plant dry mass and root to shoot ration of genotypes under study (Tetteh et al., 2020). Number of flowers per plant which is positively correlated to number of pods produced, is also greatly affected due to increased soil moisture deficit (Abayomi and Abidoye, 2009). Higher soil moisture stress levels also caused a considerable delay in the beginning and date of full flowering, according to the same study. The drop in leaf number and plant growth was ascribed to a decrease in cellular expansion as a result of reduced plant water potential and turgor as a result of decreased soil water potential. The decreased metabolic activity to compensate for the increased moisture shortage resulted in a loss in growth (Otwe et al., 2013). The crop's sensitivity to extreme drought conditions in the soil, particularly during flowering, pod setting, and pod filling stages, intensifies the frequency of flower abortion and immature pods, as well as reducing the size of the legume's seeds (Horn & Shimelis, 2020; Toudou et al., 2018). Increased leave senescence, abscission of reproductive structures, restriction of dry matter partition to the reproductive sink or seed forming variables, and a shortening of the seed filling period due to the effect of soil water deficits are all factors that contribute to the decrease in pod numbers and seed size (Ahmed et al., 2010; Toudou et al., 2018). Drought can strike in the middle of the planting season or near the end, and it has been shown to have a devastating effect on cowpea yield regardless of when it occurs. University of Ghana http://ugspace.ug.edu.gh 27 2.7 Understanding Drought: Meteorological, Agricultural, Hydrological and Socioeconomic Drought. 2.7.1 Definition of Drought The main abiotic restriction to cowpea production is drought. Unpredictable rainfall, particularly at the onset of the season, has a negative impact cowpea growth due to cultivation without irrigation particularly in the dry savanna and Sahelian regions (Agbicodo, 2009). Droughts are defined by their spatial extent (Wisner et al., 1974): national, regional, or local, as well as the type of the drought. A drought is considered national if it affects more than 10% of the population and lasts for two or more growing seasons. If output loss is significant in most ecological zones and occurs once every ten years, it is considered national. A regional drought impacts less than 10% of the population's production and lasts one or two seasons in medium and low-potential locations(UNCCD, 2015). Regional occurrence varies depending on the types of crops planted, livestock populations, and grazing patterns. Every year, in marginal agricultural zones, there is a local drought. Because the area is plagued by drought stress during the growing season, the majority of the droughts encountered in northern Ghana can be classed as local and regional(UNCCD, 2015). Droughts can be intermittent, occurring at one or more intervals during the growth season of the crops, or terminal, resulting in a steady reduction in available soil moisture content and severe drought (Ibitoye, 2015). According to Iwuagwu et al., (2017), the impacts of drought vary and are dependent on the intensity, developmental stage, and length of stress, as well as the plant's adaptive strategy for coping with the stress. University of Ghana http://ugspace.ug.edu.gh 28 2.7.2 Types of Droughts Four basic approaches have been categorized to measure drought: meteorological, hydrological, agricultural, and socioeconomic. When rainfall falls below the long-term average, a meteorological drought ensues(UNCCD, 2015) or when dry weather patterns dominate an area(Drought Basics, n.d.). The extent of dryness (in relation to some "normal" or average quantity) and the length of the dry period are commonly used to define meteorological drought. Because the atmospheric circumstances that cause a lack of precipitation vary greatly from place to region, meteorological drought definitions must be regarded region specific(Types of Droughts - JournalsOfIndia, 2021).For example when mean monthly precipitation fell below 900mm in 1983, 1992, and 2001 in Ghana, there was a meteorological drought across the country(UNCCD, 2015). It is hydrological when rainfall is much below average, causing surface and ground water reserves to be insufficient to meet all needs(UNCCD, 2015). When low water supply becomes evident in the water system(Drought Basics, n.d.). The implications of precipitation periods (including snowfall) shortage on surface or underground water supplies are known as hydrological drought (i.e., streamflow, reservoir and lake levels, groundwater). Watershed or river basin scales are frequently used to explain the frequency and severity of hydrological drought. Although all droughts begin with a lack of precipitation, hydrologists are primarily interested with how that lack of precipitation manifests itself in the hydrologic system. Hydrological droughts are frequently out of sync with meteorological and agricultural droughts, or they arrive later. Drought in agriculture occurs when evapotranspiration loss exceeds total rainfall throughout the growing season(UNCCD, 2015). It can also be when crops are affected by drought. Agricultural drought should be defined in a way that takes into consideration the varying vulnerability of crops at different stages of development, University of Ghana http://ugspace.ug.edu.gh 29 from emergence through maturity(Types of Droughts - JournalsOfIndia, 2021). Lack of moisture in the topsoil at the time of planting may hinder plant germination, resulting in low plant populations per hectare and a reduced yield. If topsoil moisture is sufficient for early development requirements, however, shortages in subsoil moisture at this point may not affect eventual output if subsoil moisture is replaced as the growing season develops or if plant water needs are met by rainfall. Drought is defined in socioeconomic terms as a condition in which the supply and demand of certain economic items are linked to components of meteorological, hydrological, and agricultural drought(Types of Droughts - JournalsOfIndia, 2021). It varies from the other types of droughts in that its occurrence is determined by supply and demand mechanisms that occur throughout time and space. This makes it difficult to define or classify droughts. Weather affects the supply of various economic items, including water, pasture, food grains, fish, and hydroelectric power(UNCCD, 2015). Water supply is abundant in some years but insufficient to meet human and environmental needs in others due to natural climate variability. When demand outpaces supply of an economic good, socioeconomic drought results, from a weather-related shortage in water supplies. 2.8 Drought coping Mechanisms in plants Drought conditions can be characterized according to their intensity (mild, moderate, and severe), the time they occur (intermittent and terminal), and the duration (short and long). Intermittent drought can occur at any point of the cowpea's vegetative growth cycle, and it's difficult to predict on an annual basis, though a general environmental trend can be identified (Chauhan et al., 2002). Terminal dryness happens at the end of a crop's growth cycle, interfering with reproductive stages such as flowering and seed formation (Nigam et al., 2002). The ability of a crop to respond to drought at different phases of development is determined by the stage of development, crop University of Ghana http://ugspace.ug.edu.gh 30 species, stress intensity and duration, and the crop's economic value (Shouse, 1979, 1981). To allow plants to deal with drought conditions, several elements and mechanisms work separately or in concert. As a result, drought resistance is a multifaceted characteristic (Krishnamurthy et al., 1996). Drought tolerance is traditionally defined as a plant's ability to live, grow, and produce well with insufficient soil water availability or under persistent water shortages (Ashley 1993). Drought escape, drought avoidance, and drought tolerance are the three types of strategies that plants adopt to handle with drought stress, according to Mitra (2001). Crop plants, on the other hand, utilize multiple mechanisms to cope with drought at the same time. 2.8.1 Drought Escape in Cowpea A plant's capacity to complete its life cycle before substantial soil and plant water deficiencies occurs is known as drought escape. Rapid phenological development (early flowering and early maturity), developmental plasticity (change in growth phase duration reliant on the level of water deprivation), and remobilization of pre-anthesis assimilates are all part of this system. Although research has proven that against a genotype with a normal life cycle, typically, a genotype with a shorter life cycle produces less (Agbicodo, 2009), drought has induced a shift to early maturing cultivars in several cowpea farming areas (Mortimore et al., 1997). Early maturity of cowpea cultivars is looked-for, and their ability to withstand drought has proven advantageous in some dry regions and years. In addition, early maturing cultivars can escape some insect infestation and severe damage caused by diseases. Cowpea cultivars adapted to low rainfall locations have been developed successfully by selection for early flowering and maturity, as well as yield testing of breeding lines under drought circumstances (Hall and Patel 1985; Cisse et al., 1997). Early maturity cowpea cultivars that withstand terminal drought (i.e., Vallenga, bengpla etc.) have been released University of Ghana http://ugspace.ug.edu.gh 31 and extensively embraced by Ghanaian farmers. These genotypes, on the other hand, fared badly when put through periodic drought during the vegetative or reproductive stages. As a result, efforts are being made to produce cowpea types that are more drought tolerant in the early, mid, and late seasons. 2.8.2 Drought Avoidance in Cowpea Plants' ability to endure high water status or cellular hydration during water stress is referred to as drought avoidance. These plants have created specialized tissues with reduced water potential sensitivity to cope in this situation. Their responses under avoidance are characterized by maximizing water uptake through the development of deep roots, minimizing water loss through stomatal control & lenticular conductance, Leaf movements, smaller leaves, the shedding older leaves and decreasing solar radiation absorption by rolling or folding leaves/paraheliotropism (Fatokun et al., 2012) and the growth of a dense trichome layer that improves reflectivity, as well as decreasing evapotranspiration surface (leaf area) (Yue et al., 2006; Taiz and Zeiger, 2006). They improve root system capacity (Jackson et al., 2000) and root properties like as thickness, depth, length, and density (e.g., in rice) to maximize water uptake (Ekanayake et al., 1985). This mechanism has an impact on efficient water utilization and evapotranspiration regulation. To assist sustain high water potentials in plant tissues, some plants grow xeromorphic features such as hairy leaves and cuticles. (Seleiman et al., 2021). Overdevelopment of these xeromorphic features reduces the production of the plants. 2.8.3 Drought Tolerance in Cowpea Drought tolerance refers is a plant's ability to cope with water scarcity and reduced tissue water potential. The method involves osmotic adjustment (solute accumulation in the cell), enhanced cell flexibility and decreased cell size, the creation of various stress-relieving chemicals, and protoplasmic resistance to desiccation (Agbicodo et al., 2010). It entails the revival and survival University of Ghana http://ugspace.ug.edu.gh 32 of genotypes following a prolonged and severe internal water shortage. Tolerant genotypes still survive when water loss in the plant is up to 95% (Scott et al., 2000). Mai-Kodomi et al., used a wooden box approach to identify two types of drought tolerance in cowpea seedlings (1999) namely the “TYPE1” and “TYPE 2”. He argued that cowpea genotypes acquired various ways to cope with extended drought in the semi-arid parts of Africa where the crop is thought to have originated, based on the two forms of tolerance responses of seedlings to drought stress. In Mai- Kodomi et al., (1999) experiment, all of the seedlings of two vulnerable lines, TVu 7778 and TVu 8256, where completely dead 15 days after the watering was stopped in Mai-Kodomi et al., (1999) trials. After the commencement of drought stress, TVu 11979 stopped growing but showed a decline in turgidity in all plant tissues, including the unifoliate and emerging tiny trifoliate, for nearly two weeks. All plant parts, including the growing tip, unifoliate, and epicotyls, died practically simultaneously. This he referred to as TYPE 1 drought tolerance. The "Type 2" drought tolerant lines, such as Dan Ila and Kanannado, on the other hand, stayed green for long and continued modest trifoliate development under drought stress, with variety wilting and dying about four weeks after drought stress began. Cowpea drought tolerance processes include stomatal closure to prevent water loss by transpiration and growth cessation (for type 1 drought avoidance) and osmotic adjustment and continuing slow growth (for type 2 drought tolerance) (Umar, 2014). Mai- Kodomo. Cowpea is a dehydration avoider with very sensitive stomata and a slow development rate (Umar, 2014). This appears to be the mechanism behind Tvu 11986 and Tvu 11979's Type 1 drought response. Dan Illa and Kanannado's type 2 reaction seem to be a blend of three mechanisms: stomata regulation (partial opening), osmotic control, and selective mobilization, displaying obvious variations in the desiccation of lower leaves versus upper leaves and developing tips (Mai-Kodomi et al., 1999). The University of Ghana http://ugspace.ug.edu.gh 33 type 2 drought tolerance mechanism appears to be more successful in prolonging the life of plants and improving their chances of recovery after the drought episode than the type 1 system. 2.9 Screening methods and approaches for drought tolerance in cowpea Cowpea drought tolerance has not been bred for as successfully as many other features(Agbicodo, 2009; B. B. Singh et al., 1997). This is partially caused by an absence of straightforward, affordable, and trustworthy screening techniques to choose plants and offspring resistant to drought from segregating populations. The degree of drought tolerance in plants has been measured using a number of different techniques. Two strategies have been put forth by researchers for screening and developing plants with drought resistance. The empirical approach, often known as the performance approach, which depends heavily on grain yield and its subcomponents is the first. The comprehensive statement of all characteristics relevant to productivity under stress is yield. The empirical approach primarily uses recombinant inbred lines (RIL) to permit the consistent evaluation of performance and understanding of genotype-by- environment interaction because the strength and incidence of naturally occurring drought stress are not completely predictable(Mustapha, 2017). Although different cowpea breeding materials, such as F2, F3, and backcross populations, have been used for drought tolerance studies in cowpea, individual lines having dispersed homozygous segments of a parental chromosome make up the recombinant inbred line (RIL) population, which was created through single seed descent of numerous selfed generations(Mustapha, 2017). The second method uses an analytical or physiological technique to pinpoint a certain physiological or morphological characteristic that will greatly boost growth and yield when drought occurs. These include characteristics like root qualities (Watanabe,1993; Matsui and Singh, 2003), leaf rolling (Mathews et al., 1990) stomata behaviour and conductance University of Ghana http://ugspace.ug.edu.gh 34 (Nkouannessi, 2005; Labuschagne et al.,2008; (Agbicodo, 2009), osmotic adjustment (Laurie, 1999), leaf membrane stability (Labuschagne et al.,2008); molecular markers (Agbicodo, 2009), and leaf wilting scales Watanabe et al., 1997; Nkouannessi, 2005; Mai-kodomi et al., 1999). However, because of the requirement to evaluate the yield of numerous lines across numerous locations and years, as well as the significant variance resulting from environmental influences and genotype-environment interactions, these empirical approaches are lengthy, tedious, and expensive. A straightforward screening method for drought resistance in cowpea was devised (Ishiyaku, 2009) based on seedling survival under water stress, and it evaluated the percentage of seedlings that wilted at the start of the drought treatment. This method identified heritable variations in the tested genotypes' responses to drought stress. The several traits used to evaluate for drought tolerance demonstrates the trait's complexity in both cowpeas and other crop species (Lawrent et al., 2013). Since it simplifies the challenges of evaluating the effects of drought on crops, leaf wilting continues to be one of the best markers of drought stress in plants (Lawrent et al., 2013). For evaluating cowpea's endurance to drought, many wilting scales have been employed including the International Board on Plant Genetic Resources devised scale of 1–9 (1 represents normal and 9 is dead under moisture stress), which has since been approved (Nkouannessi, 2005). An effective method for determining drought tolerance has been discovered to be the pot screening of genotypes at the seedling stage since it is simple to set up in a regulated environment and adaptable for screening a great quantity of genotypes (Nkouannessi, 2005). This was supported by Watanabe et al., who came to the conclusion that the process that confers seedling drought resistance also appears throughout the flowering stage (1997). Different cowpea varieties tested in wooden boxes, in the field, and in pots revealed a significant correlation between drought tolerance University of Ghana http://ugspace.ug.edu.gh 35 at the seedling stage and reproductive stage (Singh and Matsui, 2002). According to these authors, the wooden box method provided a quicker way of finding tolerant cultivars that could be kept and transplanted for additional offspring testing and selection. 2.9.1 Conventional Approach The most practical and affordable method for boosting productivity during droughts continues to be the breeding of drought-tolerant crops, but because drought tolerance is a complicated physiological and genetic feature, conventional breeding initiatives to increase drought tolerance in crops have had very modest results. Farmers' preferred cultivars can be created by identifying genotypes with genetic variability for drought resistance through conventional breeding and adopting or introgressing those introduced into the locally adapted varieties. Because there are many decisions to be made and a significant capital investment is required, the conventional technique takes a long time (sequential evaluation). A number of undesirable genes have a high possibility of being introduced into the genotype that is agronomically beneficial. Unquestionably, being early is a key characteristic in cowpea production regions that are vulnerable to drought stress. The most preferred genotypes are those that reach maturity 50 to 60 days after planting(Ngalamu et al., 2019). Additionally, as they contain the necessary genetic information, quantitative variables like the number of days to first bloom, 50% blossoming, first mature pod, and 95% maturity could be employed in selection for earliness (Owusu et al., 2017). 2.9.2 Molecular breeding The majority of crucial agronomic features are quantitatively inherited. The biggest benefit would come from improving these qualities using marker-assisted breeding because traditional plant breeding for quantitative traits is typically sluggish and challenging. The use of markers with high University of Ghana http://ugspace.ug.edu.gh 36 heritabilities during marker assisted selection may help in the selection of features with low heritabilities (Chapman et al., 2003). Other crop species have successfully had their genetics improved using contemporary techniques like marker-assisted selection (MAS) in conjunction with traditional breeding. The creation and application of molecular marker technologies and analytical methods based on biochemistry, such as restriction fragment length polymorphisms (RFLPs), random amplified polymorphic DNAs (RAPDs), amplified fragment length polymorphisms (AFLPs), and microsatellites or simple sequence repeats (SSRs), have greatly aided in the study of the structure of plant genomes and their evolution, including relationships among the Legumioseae( Timko et al., 2007; Yang et al., 2009; Huynh et al., 2016). This has greatly aided our present understanding of the structure and evolution of the cowpea genome. In order to supplement traditional breeding in cowpea, it is obvious that current biotechnology technologies must be used(Alidu, 2019). The effectiveness of plant breeding systems may be impacted by the use of molecular markers in indirect selection of agronomically significant features. Using molecular markers can help with a number of elements of plant breeding, such as identifying and removing undesired individuals during the early phases of selection, identifying individuals prior to flowering who will be helpful in transferring genes governing the favorable expression of quantitative traits, expediting the development of new varieties, especially for traits that are challenging to score, and facilitating selection for multiple traits that are simulative(Bharadwaj et al., 2011). In contrast to conventional breeding, where direct selection of traits is based on visual observation, molecular marker selection is based on molecular marker(s) strongly related to the trait of interest. University of Ghana http://ugspace.ug.edu.gh 37 2.10 Genetics of drought tolerance The foundation of any breeding program is knowledge of the genes influencing a particular trait of interest. It is important to determine and fully comprehend the genetic information relating to the gene effects and the degree of gene action controlling such qualities (Hinkossa et al., 2013). Drought and yield are two traits that are polygenically influenced and controlled by external conditions that cannot be passed from parents to offspring. For the effectiveness of breeding program, it is crucial to identify the genetic influences on these qualities. Gene effects might be additive, dominance- or epistatic-based (Gamble, 1961). The non-additive portion is made up of dominance and epistatic. The dominance may be unidirectional or ambidirectional, with positive and negative dominance occurring at distinct gene loci (Kearsey and Pooni, 1998). Allele interactions at various loci are referred to as epistasis. When the additive-dominance model cannot account for variance alone, epistatic gene activity occurs (Derera, 2005). The narrow-sense heritability, which is represented in the additive gene effects, indicates how much descendants are expected to resemble their parents (Derera, 2005). In order to analyze and comprehend the genetic foundation underlying the inheritance pattern of the characteristic of interest, information on the GCA and SCA of the parents is helpful. It calculates a line's average performance in a series of hybrid combinations (GCA) and how much a line contributes to hybrid performance in a cross with a certain other line in comparison to how much a line contributes in crosses with a variety of other lines (SCA) (Ogunbodede et al., 2000; Acquaah, 2012). The capacity to precisely identify parental pairings that will produce superior pure lines for farmers to adopt is extremely important to the breeding program's success in self-pollinating crops like cowpea. Constraints on time, space, money, and other biological factors, selecting acceptable parents and choosing good mating University of Ghana http://ugspace.ug.edu.gh 38 designs are crucial for successful plant breeding schemes (Khan et al., 2009; Acquaah, 2012; Nduwumuremy et al., 2013). University of Ghana http://ugspace.ug.edu.gh 39 CHAPTER 3 3.0 MATERIALS AND METHODS 3.1 Experimental Site The potted experiment was conducted between June, 2022 and November, 2022, at the research farm of the Department of Crop Science, University of Ghana. The experiment was conducted at a site located between latitudes 05°, 39.561° and 05°, 39.546°N and longitudes 000° 11.621° and 000° 11.641°W within the semi-arid coastal savanna zone of Ghana. This zone forms part of the sub- humid to semi-arid savanna zones., which are the biggest ecosystems of West Africa. Total annual rainfall was 800 mm with a temperature of about 27°C. The study site was nearly flat in topography. 3.2 Planting Material Two F2 cowpea populations (Tam X Hewale & Hewale X Tam) were obtained from a breeding program at the West Africa Centre for Crop Improvement (WACCI). Table 1 shows the characteristics of the two F2 cowpea populations. The F2 populations were advanced to F4.At the F4 stage, thirteen (13) top high yielding lines from both populations were selected along with the parental lines serving as checks totalling 30 lines. Table 1: Characteristics of F2 cowpea parental lines. Parental Line Days to Maturity Growth Habit Origin Trait of Interest Hewale 64-67 Erect Ghana High Yielding Tam Erect Ghana Drought tolerant 3.3 Soil Analysis Soil samples were collected on the University of Ghana farm from 0 - 20 cm depth. The soil samples were thoroughly mixed, bulked, air dried, ground and passed through an 8 mm and 2 mm sieves for filling pots. The 2 mm samples were stored in a poly bag for analysis. Soil analysis was University of Ghana http://ugspace.ug.edu.gh 40 carried out at the Department of Soil Science Laboratory of the University of Ghana, Legon. The soil (sandy clay loam) that was used was composed of 58.8% sand, 30.9% clay, 10.3% silt, 2.30 g/kg total nitrogen, 0.66 Cmol/kg of calcium, 0.56 Cmol/kg of potassium, 0.14 Cmol/kg of sodium and 0.58 Cmol/kg of magnesium. The soil has a pH of 4.6 and a bulk density of 1.43 g/cm3, organic carbon of 10.40 g/kg. 3.4 Planting A rain-out shelter was used to screen for drought tolerance and high yielding progenies from F4 population. Prior to planting F4’s, pots each measuring 5,630 cm3, were filled with 5 kg of top soil and placed in the screenhouse. The pots were watered and left overnight for sowing to be done the next day. Sowing was done at a planting depth of 4 cm in pots perforated at the base. Three seeds were sown in each pot and later thinned to one seed per pot 14 days after sowing (DAS). Seeds were sown at a distance of 0.40m * 0.40m. Every treatment consisted of thirty (30) genotypes 3.5 Fertilizer Application Fertilizer (NPK 20-20-20 + TE) was applied at optimum levels 2 weeks after the emergence of cowpea seedlings. 3.6 Weeding Weeds were controlled manually in the screenhouse throughout the experiment. To ensure a clean pot, first hand weeding was done two weeks after sowing and subsequently when necessary. 3.7 Spraying First spraying was done 14 days after sowing using the pesticides cyadim super (Dimethoate 400g/L and Cypermethrin 36g/L). Second spraying was done when flower initiation started, to control thrips (Megalurothrips sjotedti) and an early attack of Maruca (Maruca vitrata) pod borer. University of Ghana http://ugspace.ug.edu.gh 41 3.8 Harvesting and Storage Harvesting was done manually by hand picking when the pods were fully matured and dried. The harvesting was done at different days because the pods did not mature at the same time. The seeds were stored below 10% moisture content. 3.9 Drought Stress Treatment and Experimental design A total of 30 lines were laid out in Split-plot in RCBD with three replicates, with the drought treatment as the main plot and the cowpea genotypes as the subplot. There were four treatments per replicate namely; Well-watered(control), Drought at vegetative stage (VEG), drought at pod filling stage (PF) and drought at both Vegetative and Pod -filling stage (VP) on the same plant. At the initial stage, five hundred milliliters of water were added to each pot every morning before sowing to reach its 100% field capacity. The soil moisture content was determined using soil meter. Watering was stopped for each plant after the emergence of flower buds. Drought stress treatment at 0% field capacity was imposed two times. First was for 18days at the vegetative stage and the second, at the Reproductive (pod filling) stage also for 18 days. After the elapse of drought stress induction, the stressed plants received water daily at 100% field capacity up to physiological maturity. 3.11 Data collection Data was collected at the vegetative and reproductive stages on the agro-morphological traits of interest. Data were collected on the following growth parameters on individual plant basis by using the Cowpea Descriptor by IBPGR (1983) in line with the international plant genetic resources cowpea descriptors. University of Ghana http://ugspace.ug.edu.gh 42 3.11.1 Qualitative and Quantitative traits 3.11.1.1 Qualitative traits 1. Plant healthiness Overall plant healthiness was assessed on a 1 to 5 scale: 5 = green (100% health), 4 = green new trifoliate with chlorotic unifoliate and first trifoliate (75% health), 3 = chlorotic new trifoliate with necrotic unifoliate and first trifoliate (50% health), 2 = severe signs of necrotic on all leaves, with a green growing tip (25% health), 1 = dead plants (0% health). The scoring was done at 9 and 18 days after imposing stress when some of the leaves had initiated senescing till end of the experiment. The scoring was done on drought cowpea plants. 2. Stem greenness Stem greenness was scored using a scale of 1 to 5 as follows: 1 = completely yellow 2 = yellow 3 = intermediate 4 = green 5 = completely green 3. Seed size Seed size was scored using a scale of 1 to 3 as follows; 1 = small 2 = medium 3 = large 3.10.1.2 Quantitative traits 1. Plant height (cm) University of Ghana http://ugspace.ug.edu.gh 43 Plant height was measured from the base of the plant to the last stem apex by using a metallic measuring tape. 2. Stem girth (mm) Stem diameter of each genotype was measured with a digital caliper at 1.5 cm above soil surface to the nearest millimeter. The measurement was taken at the onset of drought stress imposition, 9 days and 18days after drought stress. 3. Number of leaves per plant The number of leaves were recorded for each genotype at the onset of drought stress imposition, 9 days and 18days after drought stress. 4.Mean pod length (cm) Mean length of all matured pods per plant was measured in centimeters with a rope and then placed on a rule to obtain the real measurement 5. Number of pods per plant was counted and recorded. 6. Number of days to pod maturity This was recorded as the number of days from sowing to complete yellowing of pods on each plant. At maturity, pods were harvested by hand picking, sun dried for one week and later shelled The dry grain yield for each plant was weighed and recorded. 7. Number of days to 1st flower initiation This was recorded as the number of days from sowing to the day each plant first flowered. 8. Estimation of chlorophyll content index (CII) The chlorophyll content was taken at 0, 9 and 18 days after sowing at vegetative and pod filling stages in 3 leaves of each plant using chlorophyll meter SPAD. 9. Total Grain Weight University of Ghana http://ugspace.ug.edu.gh 44 All seeds per plant were weighed on an electronic balance. 3.12 DATA ANALYSIS The variance analysis was carried out using R statistical Package. Significant means were separated using Duncan’s Multiple Range Test (DMRT) at 5% (p= 0.05) probability level-for the morphological, physiological and yield parameters. Association between the parameters studied was examined by calculating Pearson correlation coefficient (any cells with correlation values -1, their cells were colored red, cells with values of 0 were colored white and those cells with values of +1 were colored blue. Because this was a color gradient, any values between these points had a shade that represented the correlation coefficient value). Drought tolerance of the cowpea genotypes was determined by computing the drought susceptibility index using chlorophyll content, plant healthiness and stem Greenness. During the experiment, the mean air temperature and relative humidity inside the greenhouse during the day were 35 °C and 48 %, respectively. 3.12.1. Chlorophyll Inflect index By monitoring changes in chlorophyll content, each cowpea line's drought resistance was assessed using the Chlorophyll Inflect Index parameters (Gonzalez, 1996), which was estimated using the following formulas: Chlorophyll absolute decrease (CD) = CC – CS; Chlorophyll Inflect Index (CII) = 100%* CD/(CC), where CC = chlorophyll content for control, and CS = chlorophyll content for drought stress. 3.12.2 Healthiness Inflect Index "Healthiness" value was determined as follows: 100%* (5-Overall Plant Health Score-1)/4. The Healthiness Inflect Index (HII) parameter was employed using the following formulas to track University of Ghana http://ugspace.ug.edu.gh 45 changes in healthiness. Healthiness absolute decline (HD) = HC - HS; healthiness index (HII) = 100%* HD/(HC), where HC stands for control and HS for drought stress. University of Ghana http://ugspace.ug.edu.gh 46 CHAPTER FOUR 4.0 RESULTS 4.1 Chlorophyll content for different stages of drought treatment. Drought imposition lasted 18 days and differences in chlorophyll content started to show from the 9th day. Across all the 30 accessions, all three stages of drought imposition showed significant chlorophyll content drop during the last 9days of drought stress(Fig 2). Overall, drought at (PF), (VP@PF) stages dropped more than at the vegetative stage over time; few lines managed to maintain their chlorophyll contents at high levels . After the 18 days of drought imposition, Danila (33.03), TH301(30.73) and TH252(29.8) recorded the highest chlorophyll content at VEG, with Danila (37.1) still scoring the highest at VP@VEG with 37.1, HT727(18.5), TH261(16.3) and HT419(15.2) scoring the highest at PF and HT727(21.2) scoring the highest at VP@PF stages respectively (Appendix 8). CII indicated how much the chlorophyll content of that cowpea plant had changed (as a percentage) under drought stress compared with the same healthy genotype under a well-watered condition without drought stress. In comparison to the same healthy plant, the loss of chlorophyll content increases as the CII increases (i.e., the higher the CII, the more susceptible the line is). The CII value begun to rise substantially after 9 days of drought imposition. At the end of the 18days drought period, the CII value for drought at the VEG, PF, VP@VEG and VP@PF stages varied from 35.3 to 71.0, 38.8 to 100, 30.5 to 67.3 and 35.5 to 100 respectively (Appendix 9). Among the 30 lines TH71, HT402, HT540, TH252, TH301, TH54; HT141 and TA had the highest CII representing their incapacity, under drought stress, to maintain a steady chlorophyll concentration, indicating their susceptibility to drought stress conditions. On the other University of Ghana http://ugspace.ug.edu.gh 47 hand, HT700, TH301; HT727, HT419; HT727, DANILA and TH192, HT120 recorded the lowest CII indicating that these eight lines were drought tolerant (Appendix 9). Some negative values recorded indicated a low chlorophyll content in the control as compared to the treatment genotypes. This is because at the time of drought imposition, the control genotype had completed or was almost completing its phenological cycle. Fig 2. Chlorophyll content change of cowpea plant at vegetative (VEG), pod filling (PF), vegetative & pod filling at vegetative (VP@VEG) and vegetaive & pod filling at pod filling (VP@PF) stages under nonstress(red) and stressed(green) in 18days of drought imposition 0 20 40 60 N O N S TR ES S ST R ES S N O N ST R ES S ST R ES S N O N ST R ES S ST R ES S 0 9 18 C H LO R O P H YL L DAYS VEG 0 20 40 60 N O N S TR ES S ST R ES S N O N ST R ES S ST R ES S N O N ST R ES S ST R ES S 0 9 18 C H LO R O P H YL L DAYS VP@VEG 0 20 40 60 N O N S TR ES S ST R ES S N O N ST R ES S ST R ES S N O N ST R ES S ST R ES S 0 9 18 C H LO R O P H YL L DAYS PF 0 20 40 60 N O N S TR ES S ST R ES S N O N ST R ES S ST R ES S N O N ST R ES S ST R ES S 0 9 18 C H LO R O P H YL L DAYS VP@PF University of Ghana http://ugspace.ug.edu.gh 48 4.2 Overall Plant Healthiness Results for overall plant healthiness are presented in Fig. 3. The overall plant healthiness score was recorded in 18days after the drought stress treatment. The non-stressed plants grew excellently whereas the healthiness of the stressed plants dropped rapidly in the final 9 days of drought stress imposition. For day 9, overall plant healthiness varied from 98.33 to 78.33 at the VEG, 93.67 to 36.67 at the PF, 96 to 80 at the VP at VEG and 63.33 to 10 at the VP at PF stage. For day 18, overall plant healthiness varied from 52.33 to 23.33; 41.67 to 9.0; 50 to 24 and 31.67 to 5.0 at VEG, PF, VP at VEG and VP at PF (Appendix 10). In Appendix 11, change in healthiness was obtained using the last 9 days of data. Higher value percentages indicated greater plant health under drought stress, indicating the cowpea line was drought tolerant. Various percentages of the healthiness changed from 75.6% to 45.9%, 86.8% to 23.8, 75.9% to 48.3% and 87.5% to 20.9% at the VEG, PF VP@VEG and VP@PF stages respectively. Based on the healthiness change, three cowpea lines, Danila, TH209 and HT120 across VEG, PF, VP@VEG and VP@PF respectively, had the least healthiness change implying their susceptibility to drought stress. TH54, TH80 at VEG; HT471, Hewale at PF, HT120 and HT475 for VP@VEG and TH72, HT154 for VP@PF had the most substantial healthiness variation, suggesting they are drought tolerant University of Ghana http://ugspace.ug.edu.gh 49 Fig 3. Healthiness changes of cowpea plant at vegetative (VEG), pod filling (PF), vegetative & pod filling at vegetative (VP@VEG) and vegetaive & pod filling at pod filling (VP@PF) stages under nonstress(red) and stressed(green) in 18days. 0 20 40 60 80 100 N O N S T R E S S S T R E S S N O N S T R E S S S T R E S S N O N S T R E S S S T R E S S 0 9 18 H E A L T H IN E S S DAY VEG 0 20 40 60 80 100 N O N S T R E S S S T R E S S N O N S T R E S S S T R E S S N O N S T R E S S S T R E S S 0 9 18 H E A L T H IN E S S DAY PF 0 20 40 60 80 100 N O N S T R E S S S T R E S S N O N S T R E S S S T R E S S N O N S T R E S S S T R E S S 0 9 18 H E A L T H IN E S S DAY VP@PF 0 20 40 60 80 100 N O N S T R E S S S T R E S S N O N S T R E S S S T R E S S N O N S T R E S S S T R E S S 0 9 18 H E A L T H IN E S S DAY VP@VEG University of Ghana http://ugspace.ug.edu.gh 50 4.3 STEM GREENESS Results for stem greenness are presented in Fig. 4. Stem greenness scores were recorded on the 9th and 18th day after drought imposition. The plants serving as control(well-watered) had better growth condition as compared to the stressed pants whose stem greenness score dropped rapidly in the last 9 days. On the 9th day, the average plant healthiness score varied from 1 to 5 with an average of 4.50(Appendix 12). On the 18th day of drought imposition, the greenness score varied from 0.33 to 3.67 with an average of 1.99. The stem greenness change was generated using the data from the 9th and 18th day of drought imposition. A higher percentage recorded meant more greenness was kept in the drought stress condition, indicating the cowpea plant was drought tolerant (Appendix 13). University of Ghana http://ugspace.ug.edu.gh 51 Fig 4. Greenness changes of cowpea plant at vegetative (VEG), pod filling (PF), vegetative & pod filling at vegetative (VP@VEG) and vegetaive & pod filling at pod filling (VP@PF) stages under nonstress(red) and stressed(green) in 18days. 0 1 2 3 4 5 6 N O N S TR ES S ST R ES S N O N ST R ES S ST R ES S N O N ST R ES S ST R ES S 0 9 18 G R EE N ES S DAY VEG 0 1 2 3 4 5 6 N O N S TR ES S ST R ES S N O N ST R ES S ST R ES S N O N ST R ES S ST R ES S 0 9 18 G R EE N ES S DAY VP@VEG 0 1 2 3 4 5 6 N O N S TR ES S ST R ES S N O N ST R ES S ST R ES S N O N ST R ES S ST R ES S 0 9 18 G R EE N ES S DAY VP@PF 0 1 2 3 4 5 6 N O N S TR ES S ST R ES S N O N ST R ES S ST R ES S N O N ST R ES S ST R ES S 0 9 18 G R EE N ES S DAY PF University of Ghana http://ugspace.ug.edu.gh 52 4.4 CORRELATION ANALYSIS OF DROUGHT TOLERANCE TRAITS. Results for correlation analysis of drought tolerance traits are presented in Table 3. The correlation analysis revealed that the drought tolerance parameters had positive correlation between each other (Appendix 11). The correlation between CVP@PF9 and HVP@PF18 (r = 0.83) had the strongest positive linear correlation. Likewise, a strong and positive linear correlation existed between CVPF@PF9 and SGVP@PF18 (r = 0.82). There was strong significant negative correlation between SGPF9 and HV18(r = -0.58), SGPF9 and HVP@V18(r = -0.57). The results of the correlation also recorded some significant negative correlation between some parameters. HV18 and SGPF9(r = -0.58*), HVP@V9 and SGPF9(r = -0.57), CVP@PF9 and HVP@V9(R = -0.48*) University of Ghana http://ugspace.ug.edu.gh 53 Table 3. Correlation analysis of Chlorophyll decrease, stem lodging increase and healthiness change. CV9 CV18 CPF9 CPF18 CVP@V9 CVP@PV18 CVP@PF 9 CVP@PF18 HV9 HV18 HPF9 HPF18 HVP@V9 HVP@V18 HVP@PF9 HVP@FP18 SGV9 SGV18 SGPF9 SGPF18 SGVP@V9 SGVP@V18 SGVP@PF9 SGVP@PF18 CV9 1.00 CV18 0.23 1.00 CPF9 -0.23 -0.30 1.00 CPF18 -0.03 0.02 0.78 1.00 CVP@V9 0.62 -0.08 -0.06 -0.01 1.00 CVP@V18 -0.14 0.05 0.18 0.24 -0.09 1.00 CVP@PF 9 0.02 0.17 0.05 0.14 -0.21 0.02 1.00 CVP@PF18 -0.26 0.11 0.05 0.07 -0.34 0.31 0.64 1.00 HV9 0.10 -0.02 -0.38 0.12 -0.05 0.11 -0.06 -0.17 1.00 HV18 -0.11 0.49 -0.22 -0.04 -0.23 0.48 -0.21 -0.08 0.22 1.00 HPF9 0.21 -0.22 0.57 0.61 0.20 0.24 0.25 0.23 0.13 -0.27 1.00 HPF18 0.09 -0.14 0.42 0.56 0.05 0.28 0.16 0.21 0.28 -0.07 0.79 1.00 HVP@V9 0.05 -0.01 -0.12 -0.05 0.21 -0.19 -0.48 -0.26 0.26 0.01 0.07 0.14 1.00 HVP@V18 -0.03 0.37 -0.02 0.23 -0.09 0.44 -0.14 -0.09 0.34 0.79 0.04 0.02 0.23 1.00 HVP@PF9 0.03 0.08 0.17 0.39 0.09 0.04 0.61 0.56 -0.08 -0.07 0.15 0.32 -0.11 -0.15 1.00 HVP@PF18 0.06 0.20 0.09 0.16 0.04 0.09 0.83 0.51 -0.18 -0.01 0.11 0.23 -0.43 -0.18 0.78 1.00 SGV9 0.11 0.23 -0.23 0.16 -0.18 -0.05 -0.18 -0.20 0.27 0.23 -0.21 -0.19 0.08 0.25 0.04 -0.11 1.00 SGV18 0.01 0.04 -0.06 0.13 -0.09 -0.20 -0.15 -0.12 0.13 0.14 -0.05 0.02 0.08 0.08 0.16 -0.01 0.70 1.00 SGPF9 0.03 -0.37 0.27 -0.05 0.20 -0.08 0.17 0.09 -0.28 -0.58 0.39 0.27 -0.05 -0.57 0.05 0.17 -0.22 -0.07 1.00 SGPF18 0.20 -0.13 0.26 0.29 0.19 0.20 0.05 0.22 0.11 -0.16 0.62 0.83 0.24 -0.17 0.34 0.16 -0.24 0.00 0.37 1.00 SGVP@V9 0.00 0.11 -0.04 0.06 -0.12 0.22 -0.05 -0.01 0.09 0.26 0.00 0.06 -0.07 0.33 0.02 -0.04 0.47 0.44 -0.14 -0.03 1.00 SGVP@V18 -0.04 -0.07 0.06 0.15 -0.13 -0.12 0.10 0.02 0.04 0.00 0.07 0.18 -0.10 0.07 0.08 0.02 0.53 0.74 0.10 0.04 0.64 1.00 SGVP@PF9 0.22 0.11 0.17 0.42 0.05 -0.06 0.75 0.43 -0.07 -0.25 0.30 0.32 -0.32 -0.16 0.68 0.78 0.08 0.10 0.10 0.22 0.05 0.24 1.00 SGVP@PF18 0.07 0.01 0.27 0.17 -0.10 0.11 0.83 0.60 -0.19 -0.25 0.36 0.27 -0.40 -0.22 0.57 0.78 -0.31 -0.15 0.35 0.24 -0.13 0.03 0.65 1.00 *=P<0.05, ns= not significant; CV9= Chlorophyl content at vegetative stage; CPF= chlorophyll content at pod filling stage; CVP@V= chlorophyll content for vegetaive and pod filling treatment at vegetaive stage; CVP@PF= chlorophyll content for vetative and pod filling stage treatment at Pod filling stage; HV= Plant healthiness at vegetaive stage; HPF= Plant healthiness at Pod filling stage; HVP@V= Plant healthiness for vegative and pod filling trratmeent at the vegetative stage; HVP@PF=Plant healthiness for vegetative abd pod filling treatment at pod filling sage; SGV=Stem greeness at the vegetaive stage; SGPF= Stem greeness at pod filling stage; SGVP@V= Stem greeness for vegetative and pod filling stage treatment at vegetative stage; SGVP@PF=stem Greness for vetaive and pod filling treatment at Pod filling stage; 9= 9th day after drought imposition; 18= 18days after drought imposition. University of Ghana http://ugspace.ug.edu.gh 54 4.5. Factor analysis of traits towards observed variability. Results for the factor analysis are shown in Table 4. There were ten dimensions to explain the variability among the genotype of the F4 population. The first dimension (Dim1) had an eigenvalue of 5.02 and it accounted for 25.30% of the total variance. The variables associated with this dimension were PLV, PLPF, SWPF, SSPF and SSC. The second dimension (Dim 2) accounted for 17.80% of the total variance with an eigenvalue of 3.55. The second dimension was associated with SWC, SWPF, SSC, SSPF. The third dimension (Dim 3) accounted for 12.10% of the variability among the genotypes with an eigenvalue of 2.43. The major traits that contributed to Dim 3 were PPPV, SWC, SWV and SSV. The fourth dimension (Dim 4) showed an eigenvalue of 1.98 and it contributed 9.90% of the overall variances. The traits that contributed most to Dim 4 were PLC, SWC, SWPF and SSC. The fifth dimension (Dim 5) accounted for 7.08% of the total variances with an eigenvalue of 1.42. The Dim 5 was associated with SWC, PPPV, PLVP and SWVP. The sixth dimension (Dim 6) contributed 5.85% to the overall variances with an eigenvalue of 1.17. The Dim 6 was associated with SSVP, SSPF, PPPV and SPPVP. The eigenvalue of the seventh dimension (Dim 7) was 1.02 and it could explain 5.12% of the total variance. The variables SWPF, SPPVP, PLV, PLVP contributed most to Dim 7. The eighth dimension (Dim 8) accounted for 3.98% of the total variances with eigenvalue of 0.80 being associated with SPPPF, SPPVP, SWC and PPPVP. The ninth dimension (Dim 9) accounted for 4.45% of the total variances with eigenvalue of 0.69%. The main contributing variables to Dim 9 were SPPVP, PLC, PLV and PLPF. The tenth dimension (Dim 10) accounted for 2.36% of the total variance with eigenvalue of 0.47. The Dim 10 was associated PLV, SWC, SSVP and PPPV. University of Ghana http://ugspace.ug.edu.gh 55 Table 4: Factor analysis based on yield and yield related attributes of cowpea F4 population. Dim. 1 Dim. 2 Dim. 3 Dim. 4 Dim. 5 Dim. 6 Dim. 7 Dim. 8 Dim. 9 Dim.1 0 PPPC 0.41 0.21 0.50 -0.10 0.16 0.06 -0.39 -0.45 0.01 -0.08 PPPV 0.34 -0.38 0.46 0.17 0.39 0.46 -0.02 0.00 -0.01 0.12 PPPPF -0.32 -0.92 0.01 0.09 -0.09 0.07 -0.03 0.00 0.03 0.06 PPPVP 0.27 -0.24 0.20 -0.63 0.26 -0.03 -0.43 0.36 0.08 -0.11 SPPC -0.32 -0.91 0.06 0.13 -0.08 0.04 -0.07 0.03 0.06 0.02 SPPV -0.26 -0.93 0.02 0.16 -0.06 0.09 -0.09 -0.05 0.04 -0.01 SPPPF 0.36 -0.43 -0.03 0.05 0.00 -0.71 0.01 0.24 -0.15 -0.10 SPPVP 0.60 -0.07 0.18 -0.06 0.15 0.16 0.49 0.33 0.28 0.06 PLC 0.48 -0.16 -0.39 0.57 0.15 -0.15 -0.12 -0.18 0.18 -0.29 PLV 0.68 -0.10 -0.19 -0.18 -0.22 -0.31 0.09 -0.24 0.08 0.43 PLPF 0.70 -0.27 -0.14 0.14 -0.07 0.01 -0.19 -0.09 0.32 0.16 PLVP 0.26 -0.50 -0.41 -0.12 0.42 0.02 0.38 -0.21 -0.23 -0.15 SWC 0.23 0.17 0.36 0.64 0.28 -0.15 -0.21 0.27 -0.24 0.20 SWV 0.62 -0.22 0.56 -0.17 -0.38 -0.03 0.11 -0.07 -0.16 -0.11 SWPF 0.67 0.18 0.22 0.32 0.42 -0.11 0.19 -0.08 0.03 -0.03 SWVP 0.36 -0.15 -0.39 -0.68 0.42 -0.08 -0.13 -0.05 -0.01 0.07 SSC 0.67 0.09 -0.43 0.24 -0.30 0.10 -0.28 0.18 0.07 -0.07 SSV 0.62 -0.22 0.56 -0.17 -0.38 -0.03 0.11 -0.07 -0.16 -0.11 SSPF 0.76 0.13 -0.28 -0.05 -0.25 0.35 0.07 0.15 0.06 -0.15 SSVP 0.49 -0.09 -0.52 0.06 -0.08 0.33 -0.14 0.05 -0.51 0.12 Eigen values 5.05 3.55 2.43 1.98 1.42 1.17 1.02 0.80 0.69 0.47 Variances (%) 25.3 0 17.8 0 12.1 0 9.90 7.08 5.85 5.12 3.98 3.45 2.36 Cumulative Variance (%) 25.2 5 43.0 3 55.1 7 65.0 7 72.1 4 77.9 9 83.1 1 87.0 8 90.5 3 92.90 PLC=pod length of the control; PLV=Pod Length for the Vegetative stage; PLPF=Pod length for pod filling stage; PLVP=Pod length for vegetative and pod filling stage treatment; SPPC=number of seeds per pod for control; SPPV=number of seeds per pod for vegetative stage; SPPPF=number of seeds per pod for pod filling stage; SPPVP=number of seeds per pod for vegetative and pod filling stage; PPC= number of pods per plant for control;PPPV= number of pods per plant for vegetative stage; PPPPF= number of pods per plant for pod filling stage; PPPVP= number of pods per plant for vegetative and pod filling stage; SWV= seed weight for the vegetative stage; SWPF= seed weight for the pod filling stage; SWVP= seed weight for the vegetative and pod filling stage University of Ghana http://ugspace.ug.edu.gh 56 4.6 CORRELATION ANALYSIS OF YIELD AND YIELD RELATED TRAITS Pearson correlations analysis of grain yield and yield related traits showed significant (p<0.01) correlations among some of the quantitative traits: PPPPF and NSPPC were perfectly positively correlated(r=1.00) with SPPV. Seed size at the vegetative stage was also perfectly positively correlated(r=1.00) with seed weight at the VEG. Other positive and strong correlations were detected between SSPF and SSC (r=0.88), SSC and PLPF (r=0.77), SSPF and PLPF (r=0.73) and PLPF and PLV(r=0.71). On the other hand, Strong negative correlations were recorded between SWPF and SPPV (r= -0.83**), PPPPF (r= -0.86**), SPPC (r= -0.84), SSPF and SPPV(r=-0.81**), PPPPF(r=-0.82**), SPPC(r=-0.83**) (Table 5). University of Ghana http://ugspace.ug.edu.gh 57 Table 5. Correlation analysis of yield and yield related parameters PLVP SPPV PPPPF SPPC SPPPF PLC PPPV SWC PPPVP SWVP SWV SSV SPPVP SWPF PLV PLPF SSC SSPF PLVP 1 SPPV 0.28 1 PPPPF 0.29 1 1 SPPC 0.24 1 1 1 SPPPF 0.12 0.062 0.072 0.069 1 PLC 0.13 -0.3 -0.35 -0.35 0.14 1 PPPV -0.15 0.16 0.14 0.16 -0.46 -0.3 1 SWC -0.59 -0.41 -0.44 -0.39 -0.029 0.31 0.33 1 PPPVP -0.045 -0.11 -0.074 -0.077 0.01 -0.64 0.034 -0.38 1 SWVP 0.52 -0.31 -0.29 -0.32 0.059 - 0.093 -0.38 -0.58 0.63 1 SWV -0.44 -0.37 -0.36 -0.36 0.092 -0.29 0.24 0.11 0.21 -0.14 1 SSV -0.44 -0.37 -0.36 -0.36 0.092 -0.29 0.24 0.11 0.21 -0.14 1 1 SPPVP -0.12 -0.68 -0.66 -0.69 -0.1 0.049 0.26 0.19 0.086 0.14 0.54 0.54 1 SWPF -0.23 -0.83 -0.86 -0.84 -0.057 0.46 0.17 0.66 -0.21 -0.021 0.36 0.36 0.68 1 PLV 0.019 -0.65 -0.64 -0.66 0.28 0.31 -0.46 -0.13 0.018 0.45 0.43 0.43 0.48 0.44 1 PLPF -0.096 -0.52 -0.56 -0.56 0.047 0.59 -0.18 0.084 -0.13 0.17 0.31 0.31 0.43 0.5 0.71 1 PPC -0.23 -0.7 -0.72 -0.73 -0.002 0.67 -0.43 0.18 -0.23 0.14 0.15 0.15 0.39 0.51 0.68 0.77 1 SSPF -0.15 -0.81 -0.82 -0.83 -0.19 0.4 -0.21 0.05 -0.015 0.29 0.41 0.41 0.66 0.6 0.73 0.73 0.88 1 *=P<0.05, ns= not significant; PLC=pod length of the control; PLV=Pod Length at the Vegetative stage; PLPF=Pod length at pod filling stage; PLVP=Pod length for vegetative and pod filling stage treatment; SPPC=number of seeds per pod for control; SPPV=number of seeds per pod at vegetative stage; SPPPF=number of seeds per pod at pod filling stage; SPPVP=number of seeds per pod at vegetative and pod filling stage; PPC= number of pods per plant control; PPPV= number of pods per plant at vegetative stage; PPPPF= number of pods per plant at pod filling stage; PPPVP= number of pods per plant at vegetative and pod filling stage; SWV= seed weight at the vegetative stage; SWPF= seed weight at the pod filling stage; SWVP= seed weight at the vegetative and pod filling stage; University of Ghana http://ugspace.ug.edu.gh 58 4.7 GENETIC VARIABILITY OF YIELD AND YIELD RELATED ATTRIBUTES Genetic variability results are shown in Table 6. For this F4 population, all traits had low heritability (<30). Number of pods per plant had the highest heritability estimate (0.28) and seed size and seed weight recording the lowest of (0). The GCV ranged from 45.34% number of pods per plant at the vegetative stage to 1.49% for sees weight at vegetative stage and seed size at the vegetative stage. Genetic advance ranged from 0(seed weight at vegetative stage and seed size of control) to 1.94(pod length at the vegetative stage). Generally, values for PCV were high as well as those for ECV. GAM ranged from 0.06(SSV) to 49.76(PPPV). University of Ghana http://ugspace.ug.edu.gh 59 Table 6: Genetic parameters of variability for cowpea F4 population, Range Mean 𝝈𝒆 𝟐 𝝈𝒈 𝟐 𝝈𝒑 𝟐 ECV% GCV% PCV% %𝒉𝒃 𝟐 GA GAM Max Min PPPC 10 0 4.36 3.38 0.16 3.54 42.23 9.25 43.24 0.05 0.18 4.08 PPPV 5 0 1.8 1.68 0.67 2.34 72.06 45.34 85.14 0.28 0.9 49.76 PPPPF 9 0 3.09 2.89 0.4 3.26 55.01 20.41 58.68 0.21 0.42 14.62