PHD-Department of Plant and Microbial Sciences

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Browsing PHD-Department of Plant and Microbial Sciences by Subject "Drought Stress"

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    Phenotypic, Physiological Characters and Quantitative Trait Loci in F2 Generation of Phaseolus Vulgaris under Drought Stress in Machakos County, Kenya
    (Kenyatta University, 2022) Langat, Charles Kipkoech; Omwoyo Ombori; Richard C. Cheruiyot; Moses P.H. Gathaara
    Currently, yield of common bean (Phaseolus vulgaris L.) in smallholder systems in Kenya is comparatively low; standing at 400 kg ha-1 against global average of 960 kg ha-1. The low yield is attributed to drought which has become a major constraint affecting more than 60% of common bean production across the world. The most effective measure to mitigate effects of drought on common bean production is development of drought tolerant genotypes. Hence, there is need to select for drought tolerant genotypes from the local germplasm of common bean for hybridization. The current conventional method used in screening for drought tolerant bean genotypes involve long duration of field testing. Therefore, there is need to use other alternative method like, marker assisted selection (MAS) using DNA markers linked to quantitative trait loci (QTL) that could quicken the selection process and subsequent development of drought tolerant genotypes. The objectives were to; i) assess phenotypic and physiological characters associated with drought tolerance, ii) characterize F2 (KAT B1 × GLP2) population for drought tolerance using phenotypic and physiological characters, iii) determine QTLs associated with drought tolerance in an F2 (KAT B1 × GLP2) population of common bean. A series of experiments were carried out to elucidate the phenotypic and physiological characters and map quantitative trait loci (QTL) for drought tolerance in common bean. Six genotypes; KAT B1, GLP2, Nyota, Angaza, Faida and Metameta were assessed in a rain-out shelter under water stress for phenotypic and physiological characters related to drought tolerance. Characterization of phenotypic and physiological characters was also carried out in F2 population consisting 116 individuals previously developed from KAT B1 × GLP2 cross. The F2 population comprising of 120 lines derived from KAT B1 and GLP2 were mapped for quantitative trait loci (QTL) linked with drought tolerance. The experiments were laid out in a randomized complete block design replicated three times. Stomatal conductance and stem biomass showed greatest variation among genotypes and had significant positive correlations with yield per plant under water stress. Estimates of expected genetic advance indicated that high gains and progress are attainable on genotypic selection for characters such as days to maturity, pod number plant-1, stomatal conductance and leaf water potential at 34.97 %, 22.32 %, 22.87 % and 25.46 % respectively. High estimate values for heritability in broad sense were also obtained for these characters. A genetic linkage map with a total length spanning 634 cM of the common bean genome at an average distance of 2.02 cM between adjacent markers was generated using 229 single nucleotide polymorphism (SNP) markers. A total of twenty three QTLs were detected for the branch numbers, pod numbers, grain number per pod, stem biomass, leaf biomass, pod biomass, days to flowering and maturity, 100-seed weight, seed yield, stomatal conductance and leaf water potential. Two putative QTLs involved in drought adaptation mechanisms were detected; SCO4.1KG associated with stomatal conductance on chromosome Pv04 and LWP1.1KG associated with leaf water potential chromosome Pv01. Overall, this research provided insight into the genomic regions (QTLs) controlling traits related to drought tolerance in common bean. Given the long duration taken in developing improved common bean cultivars using conventional phenotypic selection, the identified QTLs should be incorporated in marker assisted selection in screening and selection of high yielding and drought tolerant genotypes hence, hastening common bean improvement efforts.