Analysis of genetic diversity and progress made in bean breeding in Uganda

Abstract

Over the past 56 years, many cultivars of common beans have been released in Uganda but the genetic gain made in grain yield and related traits have never been documented. The morphological and genetic diversity of these released bean varieties is important in identifying potential varieties with desirable traits that could be used as parents for future hybridization schemes but this has also not been elucidated. Therefore, the objective of this study was to analyze the diversity and progress made by bean breeding in Uganda over the past 56 years. The study used 40 varieties and was conducted at the National Crops Resources Research Institutes (NaCRRI) Namulonge and at Kwachwekano and Nakabango Zonal Agricultural research institutes during the first and the second seasons of (2017B and 2018A). The Climbing types were planted in a randomized complete block design (RCBD) with three replications while a 3x10 alpha-lattice design with three replications was used for the bush types. To assess the morphological diversity, seven qualitative and seven quantitative traits were measured on five randomly selected plants. Analysis of variance was used to detect level of significance among the quantitative traits at P=0.05. Genotypic coefficient of variation (GCV) was also determined. Dendrogram were created with Euclidean similarity coefficients in Genstat 18th edition. SSR markers were used to test for the genetic diversity. The gene diversity index, number of polymorphic loci and allele frequencies were generated using Powermarker3.25software.The dendrogram using the similarity coefficients was generated. Analysis of variance revealed highly significant differences at P<0.001. High (GCV) was observed in number of seeds per pod followed by hundred seed weight and number of pods per plants (NPP) and Bean Common Mosaic Virus(BCMV). Cluster analysis showed two majors groups formed based on gene pool or the centre of origin. The polymorphic information content (PIC) ranged from0.16 to 0.37 and the gene diversity index ranged from 0.18 to 0.50 implying moderate diversity. Cluster analysis segregated the bean samples into two major clusters based on growth habit. The relative genetic gain was 1.27% /year for bushy types and 1.54%/ year for the climbing types. The gain achieved in introducing resistance to BCMV in both types was 0.9% and 1.8 % over the years. This characterization can be used for selecting parents for further improvement. Key words: Phaseolus vulgaris; morphological/genetic diversity, Genetic progress, Annual rate of gain.