Multi-environment phenotyping of ricebean (Vigna umbellata (Thunb.) Ohwi & Ohashi) germplasm and identification of core set for accelerating the crop improvement programs

Ricebean ( Vigna umbellata ) is a nutrient-rich rich underutilised legume crop. It is primarily grown in the uplands of India, Nepal and China. Despite its adaptation to a wide range of agroclimatic zones and resistance to various biotic and abiotic stresses, ricebean crop improvement efforts have been slow mainly because of the low levels of genetic diversity utilised in ricebean breeding. This study presents the first multi-environment phenotyping and core collection building in ricebean with 1,589 accessions maintained at the Indian National Gene Bank. The accessions were assessed in two diverse agro-ecological regions (New Delhi and Almora), indicating significant phenotypic variations for important economic traits such as days to flowering, pod length, number of seeds per pod, and seed weight. The core subsets were sampled using MStrat, PowerCore and PCSS, and CoreHunter algorithms. The sampled coresets were evaluated using diversity indices such as genetic distance, mean difference percentage (MD%), variance difference percentage (VD%), coincidence rate (CR) and variable rate of coefficient of variation. The E-EN100 approach of CoreHunter yielded the most effective representation, resulting in a final core set with 251 accessions (14.3% from the entire collection). Diversity indices, clustering methods, QQ-plots, and distributional comparisons confirmed the representativeness of the core set. Multi-environment GGE biplot analysis identified stable and high-performing accessions for early flowering, synchronous maturity, pod and seed traits, including promising genotypes such as IC351508 and IC352944 with determinate growth habit and high yield potential. The study provides a manageable subset of the entire collection, which may play a significant role in trait discovery and ricebean cultivar development.