Common Bean Phaseolus Vulgaris L Root Phenotypes As A Tool For Developing Bean Genotypes With Superior Adaptation To Low Phosphorus Availability And Drought

Common bean is one of the most important legume crops especially in developing countries like eastern and southern Africa. Though bean is important in these areas its production is affected by a number of abiotic stresses including low soil fertility and drought. However, in these countries the population growth rate is increasing therefore, there is need to find mechanisms to increase crop productivity. Previous studies on bean roots have shown that bean genotypes vary for root phenotypes, which enhance drought and low phosphorus tolerance. These traits include basal root whorl number, basal root number, adventitious roots, root etiolation, root growth angle and root hairs. These traits can be regulated by genes, by the environment or both. In Africa farmers have different preferences for different bean genotypes depending on color, seed size, resistant to stresses and maturity period. Hence in developing new bean cultivars, farmer's preferences should be taken into consideration. In this study we evaluated phenotypic variation for a number of root traits and their relation to phosphorus uptake. The genotypes which we evaluated in this study were first screened in another study, which evaluated bean genotypes for superior adaptation to low soil fertility and drought, this study was the Bean Improvement for Low Soil Fertility in Africa (BILFA) program. These genotypes were found to have varying performance under low soil fertility and drought. From that BILFA study we selected eleven genotypes to be used in our study and four non-BILFA genotypes making a total of fifteen genotypes. These non-BILFA lines are commercial cultivars in Malawi. Our study included both greenhouse and field experiments. The fifteen genotypes were phenotyped for root traits. Our data from the phenotyping study showed that the existing cultivars had less basal root whorl number compared to the BILFA lines. In an attempt to improve the adaptation of these cultivars to low phosphorus availability, we attempted to increase their basal root whorl number by hybridization between these commercial varieties, which have one whorl with four whorled genotypes.