College of Basic and Applied Sciences

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    Genetic Studies and QTL Mapping of Drought Related Traits in a Sweetpotato (Ipomea Batatas(L.) Bi-Parental Mapping Population
    (University of Ghana, 2018-12) Utoblo, O.G.
    The study was carried out to understand the genetic basis for yield under drought environments, and to map quantitative trait loci associated with yield and yield related components under drought stress in sweetpotato. The sweetpotato BxT mapping population, generated from a cross between sweetpotato varieties Beauregard and Tanzania was used for this study. Genotypes were evaluated in irrigated and drought environments to evaluate the effect of drought on yield and yield related parameters as well as genetic variability under drought conditions. Drought affected root yield, foliage yield, biomass and harvest index at varying degrees, with highest relative yield reduction in root yield. Drought tolerance indices were estimated based on root yield under drought and irrigated conditions. Suitable drought tolerance indices identified were geometric mean productivity, mean productivity and drought tolerance index. Genotypes were grouped as drought tolerant and high yielding (DTHY), drought tolerant and low yielding (DTLY), drought susceptible and high yielding (DSHY) and drought susceptible and low yielding (DSLY) based on their root yield means. Drought also reduced chlorophyll content, leaf area, normalized difference vegetation index (NDVI), photosynthetically active radiation, and increased canopy temperature. Observed low heritability and non-significant variation among genotypes for physiological traits indicates inefficiency of these traits for selection of drought tolerant genotypes in the BxT mapping population. However, morphological traits had significant variability among genotypes, high to moderate heritability under drought stress indicating they could be considered as potential secondary traits for selection of drought tolerant genotypes. To understand the genetic basis of drought tolerance in sweetpotato, QTLs associated with yield and yield related components under irrigated, drought and rainfed conditions were mapped using the genotype by sequencing method, GBSpoly. The occurrence of four QTLs on linkage group 9 in single environments and on linkage groups 11 and 6 for combined environments under only drought stressed conditions is indicative of drought specific QTLs. With further studies, confirmation and validation of these QTLs may be useful for drought tolerance-oriented breeding programmes in sweetpotato
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    Genetic and Genomic Resources to Improve Resilience to Striga [Striga Gesnerioides (Wild.) Vatke] and Drought in Cowpea
    (University of Ghana, 2018-12) Diangar, M.M.
    Cowpea (Vigna unguiculatan (L.) Walp.) is a grain legume cultivated worldwide in over 14 million ha but its productivity in Senegal is seriously affected by the infestation of Striga gesnerioides (Wild.) Vatke, a parasitic weed. Striga resistance is an important trait that is missing to most cultivated varieties in Senegal. Its negative effect on cowpea is exacerbated by drought which is a threat to agriculture. The present dissertation describes various options taken on the improvement of cowpea for Striga resistance and drought tolerance using microsatellite markers and drought tolerance indices and cultivar superiority coefficients. The first breeding activity describes methods and results obtained in identifying farmer concerns and interest on profile of their desired ideotype in Louga, Kebemer and Tivavouane involving 109 farmers. The second breeding activity was conducted in response to Participatory Rural Appraisal (PRA) indication on major constraints to anticipate on pre-breeding in order to identify drought tolerant lines that can be used as parental lines in developing new varieties. This study used phenotypic data recorded from well-watered and water-stressed experimental fields in Bambey (ISRA, CNRA de Bambey) and involved 112 accessions from the Senegalese cowpea breeding programme. The third breeding activity focused on cowpea resistance to Striga gesnerioides using Marker-assisted selection (MAS). The different options deployed involved in MAS were the creation of bi-parental lines of hybrids, RIL populations and advanced backcross populations using Marker-assisted backcrossing (MABC), the validation of resistance of the developed backcross lines in field in natural infestation and the identification of loci associated to Striga resistance in cowpea using Genome-Wide Association Analysis (GWAS) on a wide population composed of 367 unrelated accessions from diverse origins in the word. PRA revealed that drought was the major constraint to cowpea production and farmers were interested in large and brown seeded cowpea grain type in Senegal. Striga was important only in some divisions. Preliminary field and pot screening identified several lines more tolerant to drought compared to best tolerant check Mouride, reliability of markers used in MABC were weak, resistant BC4 lines performed unexpectedly in field in regards to SNP screening predictions. Significant markers were identified in 2 environments out of 4. Six candidate genes were identified in regions neighbouring identified markers and annotated. SNPs identified were not reported before in any article to best of our knowledge. The identified genetic and genomic resources could be used in population development for drought tolerance and S. gesnerioides resistance in cowpea.
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    Genetic Improvement of Local Sorghum (Sorghum Bicolor L. Moench) Varieties for Drought Tolerance
    (2015-12) Ouedraogo, N.; Sanou, J; Danquah, E. Y; Tongoona, P; Vernon, G; University Of Ghana,College of Basic and Applied Sciences,West Africa Centre for Crop Improvement
    Drought is the major abiotic factor limiting crop production worldwide. Sorghum is one of the most drought tolerant grain crops that have the ability of addressing food insecurity in semi-arid areas. However, it is exposed recurrently to severe forms of drought and, therefore, requires improvement to cope with moisture stress. The present investigation was undertaken to improve local sorghum varieties for drought tolerance in Burkina Faso. A participatory Rural Appraisal was conducted to identify farmers’ constraints and to determine their preferred sorghum varieties. One hundred and ten accessions, including improved and introduced materials, were assessed in full irrigated and terminal drought conditions in an alpha lattice design to identify drought tolerant and high yielding genotypes. A molecular characterization using 26 SSRs markers was conducted with the same accessions to determine the genetic diversity, genetic differentiation and the level of homozygosity of these accessions. Finally, marker-assisted backcrossing was carried out to introgress stay-green QTLs into four farmers’ preferred varieties. The major constraint limiting sorghum production in Burkina Faso was Striga, a parasiticweed. Drought was the second most important factor reducing sorghum yield and the most important abiotic constraint. The study revealed that terminal moisture stress was the most frequent type of drought but has less effect on yield than pre-flowering drought. Forty seven per cent of farmers rely preferentially on their local landraces. A few preferred improved varieties derived from local landraces, over high yielding exotic (introduced) varieties. Among released varieties, farmers grew more Kapelga in all different climatic zones of the country. There was a strong correlation between grain filling rates, yield under stress, grain number, Stress Tolerance Index (STI) and Geometric Mean Productivity (GMP). This indicates that improvement can be achieved using accessions with high STI and GMP indices. Classification based on yield and its components, divided accessions into three main groups. Grinkan was the highest yielding and most drought tolerant genotype in the study. A group of high yielding and drought susceptible accessions were identified including local improved varieties and landraces that performed well under non-stressed conditions and were susceptible to terminal drought. Low yielding and drought tolerant accessions were also identified. Genotypes with high STI indices could be used by farmers to ensure optimal production in drought prone areas and in breeding programs. There was low gene diversity of 0.34 compared to previous molecular studies in Burkina Faso. The Fixation index (Fst) value exhibited low genetic differentiation among populations and moderate genetic differentiation between local population and exotic materials. The local accessions have a high level of homozygosity. Five stay-green QTLs (Stg1, Stg2, Stg3, Stg4 and StgB) were incorporated into four recurrent (Kapelga, Sariaso09, Sariaso01 and Grinkan) backgrounds. The BC1F1 lines which carried at least one QTL included eighteen (18) progenies from Sariaso09 and two from Kapelga which were heterozygous at all marker loci flanking the target QTLs. Four, three and four progenies, respectively, from Grinkan, Kapelga and Sariaso01 carried fourQTLs. Only one plant, GB7, carried three major QTLs (Stg1, Stg2 and Stg4). Seven,four, three and one progenies, respectively, from Sariaso09, Kapelga, Grinkan and Sariaso01 carried two stay-green QTLs. Fifteen, one and one progenies, respectively, from Sariaso09, Kapelga and Sariaso01 carried one QTL for stay-green. The screening using background markers identified progenies with different recovery rates of the recurrent parent genome. A majority of the progenies recovered less than 75% of the recurrent parent genome. Two progenies (GB8 and S1B3) recovered 75% of their recurrent parent genome. Three (S9B73, KB4 and GB7), two (S9B48 and KB16) and one (S1B6) progenies had respectively recovered 78%, 81% and 83% of the recurrent parent. The best 30 accessions identified through phenotypic evaluation and the promising advanced introgression lines should be evaluated in different locations for possible release as commercial varieties. In the future, drought tolerant lines developed through MABC and high yielding lines could help stakeholders to improve their sorghum production, and, therefore, contribute to ensure food security in Burkina Faso.
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    Genetic Analysis of Drought Tolerance in Cowpea [Vigna Unguiculata (L.) Walp]
    (University Of Ghana, 2015-12) Olubunmi, D.I.; Tongoona, T.; OFFEI, K .S Offei, S.; Blay, E.T.; Boukar, O.; University Of Ghana, College of Basic and Applied Sciences, School of Agriculture,Department of Crop Science
    Agriculture in Sub Saharan Africa (SSA) is under serious threat due to water shortage, population pressure and climate change. Cowpea, a protein-rich legume crop complements staple cereal and tuber crops in the diets of rural and urban people of the tropical and sub-tropical regions of the world. It therefore, plays a significant role in the sustainability of food and nutrition security in SSA. Cowpea, though reported to be inherently drought tolerant; but because it is mostly grown under rain-fed conditions towards the end of the rainy season in the drier parts of Nigeria, its productivity is still being adversely affected by the erratic pattern of rainfall which occurs frequently in these areas. Increasing the level of drought tolerance in existing cowpea varieties that will possess farmers’ preferred traits will increase farmers’ adoption of these varieties and ensure high and stable yield from farmers’ fields under the ever changing climatic conditions. The objectives of this study were therefore, to: (i) identify the impact of drought on cowpea production and farmers’ preferred traits in new cowpea varieties (ii) assess the diversity of cowpea germplasm for drought tolerance (iii) assess the combining ability of cowpea lines under drought and well-watered conditions and (iv) determine the gene action controlling drought tolerance in cowpea. The results of a Participatory Rural Appraisal (PRA) conducted in fifteen cowpea growing communities of Kano State, Nigeria established that drought, pests and diseases were major constraints to cowpea production. Drought reduced grain yield and fodder yield to about 62% and 56% of realizable yield under normal condition respectively. Fifty-eight percent of the farmers confirmed drought at the flowering / pod-filling stage was more devastating than drought occurring at the vegetative stage (32%) while 10% of the farmers confirmed that both growth stages were both growth stages are susceptible to University of Ghana http drought. Consumer-based traits such as large seed, short cooking time and dual-purpose varieties which increase farmers’ income were identified as important preferred traits as well as traits for biotic and abiotic tolerances in new cowpea varieties. Ninety-one cowpea varieties were screened for tolerance to drought using the wooden box screening technique with the aim to identify parents to be used for genetic analysis studies. Twenty lines were selected based on their responses to the screening and were mated in a North Carolina Design II to generate 100 single F1 crosses. The F1 progenies and their parents were evaluated under drought and well-watered conditions at two locations. Grain yield of the F1 progenies ranged between 2533 kg ha-1 for TVu6707 x TVu9797 and 18 kg ha-1 for TVu11986 x TVu2736 under drought stress, 3786 kg ha-1 for TVu6707 x TVu9797 and 45 kg ha-1 for TVu633 x TVu2736 under well-watered conditions. General Combining Ability (GCA) and Specific Combining Ability (SCA) mean squares were significant for grain yield and other traits across all research environments indicating that both additive and non-additive gene effects were important in the control of grain yield and other drought adaptive traits across all research environments. The contribution of GCA (71%) to the total sum of squares was higher than that of SCA (21%) for grain yield under drought stress indicating that additive gene action was more important in the inheritance of grain yield under drought stress. Similarly, the superior positive GCA (GCA-female and GCA-male) effects for 100-seed weight, number of seeds per pod, Normalized Difference Vegetation Index (NDVI) measured at three different growth stages, the number of pods and seeds per plant under drought stress indicated that additive gene action was more important in the inheritance of these yield related traits under drought stress. The lines TVu79, TVu6707, TVu9693 and TVu9707 were identified as general good combiners with outstanding. positive GCA effects for grain yield under drought stress. These can be used as parents to generate improved cowpea varieties for drought tolerance. Considering both mean yield and stability performance, TVu8670 x Sanzi, IT89D-288 x TVu8670, TVu6707 x TVu79 and TVu8670 x TVu79 can further be advanced for development of novel drought tolerant varieties.