Variability study and genome-wide association mapping for cooking time in common BEAN (Phaseolus vulgaris L.) Genotypes

Common bean (Phaseolus vulgaris L.) is an important component of the production systems and a major source of protein for the poor in Eastern and Southern Africa. Information on genetic variability is prerequisite for further improvement of the crop. However, there is little information regarding variability study in the present genotypes of common bean. One of the major factors that limit greater utilization of beans is their long cooking times compared to other foods. So far, very little is known about the genomic regions involved in determining cooking time. The overall objective was to study the extent of genetic variation and association among grain yield and yield-related traits as well as to use genome-wide association analysis to identify genomic regions involved in determining cooking time. Four hundred twenty three genotype were tested in an augmented design at Hawassa Agricultural Research Centre in Southern Region of Ethiopia, in 2015. Analysis of variance revealed that the genotypes differ significantly for all the characters studied except for leaf chlorophyll content, pod harvest index and hundred seed weight. High phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV) were recorded for vertical root pulling force resistance and number of pod per plant. High GCV along with high heritability and genetic advance was obtained for number of pods per plant. Grain yield had positive and highly significant phenotypic and genotypic correlation with days to maturity, plant height, vertical root pooling force resistance and number of pod per plant. Path analysis revealed that plant height, days to maturity and pod per plant shows high and positive direct effect on grain yield. These three characters can be considered for selection. The D2 analysis showed the 423 genotypes grouped into twenty-one clusters. This makes the genotypes to become moderately divergent. The x2 test showed that all inter-cluster squared distance were highly significant at P<0.01. Principal component analysis showed that the first four principal components explained about 66.19 % of the total variation. In this study high variation for cooking time was observed and eleven common bean genotypes were identified which cook in less than 17 min. GWAS showed that, significant SNP associated with cooking time were found on chromosomes Pv04, Pv05, and Pv09.The associated markers are possible candidates for marker-assisted selection to improve cooking time trait. Further studies of common bean genotypes with larger sample size in different location should be conducted on common bean variability in order to give confirmative results. The significant markers need to be validated in different environments before their use in marker-assisted selection. This research serves as an important base for further studies to understand the genetic control of cooking time in common bean