Ricebean is an underutilised grain legume grown mainly in marginal hill areas in northern India and Nepal It belongs to the Ceratropis genus, section Angulares, and is believed to be a domesticated form of V. umbellata var. gracilis, a cross-fertile wild type native to Indo-China. It is closely related to adzuki bean, V. angularis.
Although ricebean has high nutritional quality and plays an important role in food security and in the farming systems in the areas to which it is adapted, very little work has ever been done on the crop, and there has been no modern plant breeding, despite its very high phenotypic diversity.
A stratified sample of 27 ricebean genotypes from Nepal, sampled on diversity in local names, geographical origin, agro-environment, growth habit and seed traits, was selected to cover the range of diversity, together with a bold (large)-seeded check and an adzuki bean check. DNA was extracted using the modified CTAB method, and used for simple sequence repeats (SSR) analysis: a total of 109 primer pairs mapped on an existing adzuki bean linkage map, were used to identify primers detecting polymorphism in ricebean.
Forty nine of these gave amplified products, with 93 DNA products detected. Of these, 35 SSRs were polymorphic, with 2-4 alleles per primer for the whole set including the adzuki bean check. Eleven of these primers contained AG repeats: one had AAG repeats and another GT(AT)AG repeats. They belonged to linkage groups 1, 2, 3, 6, 8, 10 and 11 of the ricebean genome, and explained the variation at the DNA level both between the ricebean accessions and between ricebean and adzuki bean. Although the ricebean accessions were diverse, they showed less diversity than had been expected. Dendrograms were constructed based on UPGMA analysis to compare the groupings and identify the primers that best described the ricebean diversity. Three accession from the mid to high-hills in the far west of Nepal, which had indeterminate growth habit, clustered close to adzuki bean when grouped using eight polymorphic primers with more than three bands per primer. Two of these were also close when clustering used the 13 polymorphic primers with PIC greater than the average found.
The primers identified will be used in the next phase of the work, which is to assess molecular marker diversity in ricebean landraces selected for their good performance in the field trials held in 2006/07.
