Assessment of genetic diversity and population structure of Zambian common bean landraces

Abstract

Analysis of relationships among common bean landrace populations through genetic diversity and population structure using both molecular and agro-morphological methods and their comparisons provide complementary information for crop improvement, conservation and landrace registration programmes. However, such information is not available for Zambian common bean landraces. To fill this gap, thirty agro-morphological traits and 20 SSR markers were used on 124 individuals and on over 1100 individuals of four landraces to study agro-morphological and genetic diversity respectively among these landraces, assess the genetic changes that occur over the three growing seasons, the correlations among the agro-morphological traits, nutritional variations, and classify the accessions into the two genepools based on both markers using reference genotypes from CIAT. The results from these studies showed that there is a very high genetic diversity at molecular (0.605) and agro-morphological (0.404) levels for the landraces, commercial varieties and CIAT reference lines overall. Molecular diversity showed higher values in the landraces than commercial varieties and CIAT reference lines (0.517 vs 0.253). The same was true for agro-morphological diversity (0.469 vs 0.146). At molecular level, there was a high rate of gene flow amongst these landraces (Nm = 0.3906). There was no significant differences (p < 0.05) in genetic diversity and population structure among the the three growing seasons for the landraces. Morphological characters showed very strong correlations amongst themselves such as Pod length vs days to flowering, average seed weight per plant vs days to flowering and 100 seed weight to days to maturity. There was a significant (P < 0.05) differences in the mineral concentrations between the landraces, commercial varieties and CIAT reference lines. Twenty three and twenty six sub-populations with iron and zinc content higher than averages respectively were identified. There was no significant difference (p<0.05) for mineral concentration based on seed colour although yellow, red, maroon, and black seed colours were associasted with high mineral contents. A strong positive correlations were exhibited among the mineral concentrations, for example Zn vs Fe (r = 0.764). The four landraces were identified as Lusaka yellow and Lundazi being mostly Andean beans, and Mbala mixture and Solwezi being mostly Mesoamerican beans. Overall, Mesoamerican beans (54%) dominate these common bean landraces from Zambia. These results demonstrate a lot of practical importance in maintaining genetic diversity and biofortification that can be achieved through incorporating these landraces in to the Zambian bean breeding program, in addition to facilitating landrace registration, and landrace seed conservation.

Date of Award	10 Dec 2018
Original language	English
Awarding Institution	University of Bath
Sponsors	Crop Innovations & Self Help Africa
Supervisor	John Beeching (Supervisor) & Roderick Scott (Supervisor)