Screening For Drought Tolerance Potential Of Nine Cocoa (Theobroma Cacao L.) Genotypes From Cocoa Research Institute Of Ghana (Crig)
Date
2016-06
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Publisher
University of Ghana
Abstract
Theobroma cacao L. (cocoa), a tropical forest understory plant, is very important for the chocolate industry and the economy of many developing countries in the tropics. However, cocoa production is under threat from climate change due to the general intolerance of the crop to drought. In Ghana, cocoa production is threatened by erratic weather patterns and the shifting of the cocoa belt southwards (particularly south of Brong-Ahafo region) due to the gradual extension of the dry savannah areas from the Northern regions of the country as a result of climate change. Thus, there is the need to develop drought-tolerant cocoa plants that can help not only to sustain but also boost cocoa production in the country. Consequently, two experiments were conducted in a shed constructed at the premises of the Department of Botany, University of Ghana, designed to keep out rain and simulate the shading required for establishment of cocoa seedlings. The two experiments were conducted between January – February 2016 and April – May 2016 in order to i) determine the drought-tolerance potential of nine (9) selected cocoa genotypes (T60 x Pound10, PA7 x 6035, T85 x PA7, T63/971 x Sca9, PA150 x 6020, AMAZ X 9006, T79 x 9006, PA150 x 6020 and PA7 x MAN) and ii) identify the relationship between their physiological and biochemical parameters under drought stress and their drought-tolerance ability so that these could be used as sources of traits for the development of drought-tolerant cocoa hybrids. In the First Experiment (Phase I), a Randomized Complete Block Design (RCBD) with three (3) replicates was used to rapidly assess the drought tolerance potentials of the 10 genotypes of cocoa at the seedling stage and determine the effect of small differences in age of seedlings on their drought-tolerance potential. The seedlings were slowly saturated with water to Full Saturation (FS) after which water was withheld from 27 out of 54 seedlings comprising of three (3) replicates of each of the nine (9) genotypes one (1) Day After Full Saturation (DAFS) (Water stressed); whereas the remaining 30 seedlings (Control) received water every other day till the end of the experiment. Data on leaf Relative Water Content (RWC) and Soil Moisture Content (SMC) were collected in addition to the number of days for First Appearance of Drought Symptoms (FADS). Data on Leaf Relative Water Content (RWC) and Soil Moisture Content were taken at i) the beginning of the experiment i.e. 1DAFS and ii) First Appearance of Drought Symptoms (FADS). Based on the results of Experiment I, the genotypes were ranked using the number of days it took for FADS to appear in the selected cocoa genotypes. Further studies were conducted on the genotypes in Phase II (Experiment II). Experiment II was designed as a Randomised Complete Block Design (RCBD) with six replicates of each genotype. The free proline content of the leaves was used as a biochemical criterion for drought-tolerance potential. The selected genotypes differed in their drought-tolerance potential. Proline was observed to accumulate in water-stressed seedlings, and the differences in the mean proline accumulation in the genotypes was found to be statistically significant. There was no positive correlation between the accumulation of free proline of most of the genotypes and the relative water content of the leaves except for T63 x SCA9 and T60 x POUND10; T63 x SCA9 and T60 x POUND10 stood seemed to be the most drought-tolerant genotypes resulting from their relatively high leaf RWC and low water use. Free proline accumulation could be used broadly to distinguish between drought-tolerant and drought-sensitive varieties. The number of trichomes present on the leaves of the various genotypes could also broadly be used to distinguish between drought-tolerant and drought-sensitive varieties of the cocoa genotypes. Further studies should be carried out to investigate the role of proline accumulated in drought-stressed cocoa plants as well as the other factors e.g. presence of trichomes that can contribute to the low water use of the genotypes that showed higher drought-tolerance potentials.
Description
Thesis (MPhil)
Keywords
Drought Tolerance, Cocoa (Theobroma Cacao L.), Genotypes, Cocoa Research Institute Of Ghana