Genetic And Physiological Studies On Drought Resistance Traits In Dry Bean (phaseolus Vulgaris_l.) In Kenya
Field and trough studies were conducted to evaluate response of physiological and morphological traits of dry bean tPhaseolus vulgaris L.) genotypes to water stress over a period of two seasons. Thirty six bean genotypes were subjected to two watering levels (irrigated and not irrigated). Relative water content (RWC) , leaf water potential (LWP) , relative growth rate (RGR) , days to 50% flower (DTF) , taproot length (TRL) and root dry weight (RDW) were measured. High and low scoring genotypes with respect to RWC, LWP, TRL and RDW were identified and crosses made between them in genetic studies. Results indicated significant genotypic differences in all the parameters. Water stressed plants maintained lower RWC and LWP than non-stressed plants. They also manifested faster growth in root length but had lower root dry weights than the non-stressed plants. Water stressed plants also flowered in shorter period than non-stressed plants. Significant positive correlations were observed between LWP and RWC as well as TRL and RGR. Genetic studies showed that RWC was predominantly influenced by additive (d) and additive x dominance (j) genetic effects. Additive x dominance (j) genetic effects were predominant in taproot length while additive (d) and additive x dominance (j) genetic effects influenced root dry weight. LWP was largely controlled by additive (d) genetic effects. These results indicate that there is a genetic pool of variation in terms of the measured parameters which can be exploited in bean improvement for adaptation to semi-arid areas. The genetic effects imply that selection procedures that exploit epistatic genetic effects may be used in improvement programmes which target RWC and root growth as selection indicators. Delayed selection of these parameters beyond F3 and later generations and then using bulk-pedigree breeding method is suggested. On the other hand, high LWP would be best selected for by using pedigree and backcross breeding methods.