Engineering genetic diversity: Optimising gamma ray mutagenesis in yam bean variety RM-1 for future trait development

Yam bean (Pachyrhizus erosus L. Urban) is an underutilised legume-tuber crop valued for its high root yield, rich nutritional composition and ability to enhance soil fertility through biological nitrogen fixation. Its seeds also contain rotenone, a natural insecticide, adding to its agricultural relevance. Due to its drought tolerance and adaptability, yam bean is considered a promising crop for sustainable and climate-resilient agriculture. However, progress in its improvement is constrained by a narrow genetic base. Given the absence of mutant varieties in India, the present study evaluated the effects of gamma radiation on the yam bean variety RM-1. Dry seeds were irradiated with doses ranging from 50 to 200 Gy to determine the lethal dose 50 (LD₅₀). Based on the seedling vigour index (SVI), which showed a strong inverse dose-response correlation and up to 85 % reduction compared to the control, the LD₅₀ was estimated at 177.13 Gy. Subsequent M1 field evaluation (140–200 Gy) indicated a similar decline in seedling survival, reaffirming gamma-induced genotoxic effects. The M1 generation exhibited considerable variation in stem colour (e.g., green with brown stripes) and leaf morphology (obcordate, narrow, or wrinkled). The greatest morphological diversity appeared at 180–200 Gy, while chlorophyll mutants-mainly xantha and chlorina-were more frequent at 140 Gy, indicating mutant saturation at higher doses. These findings highlight gamma radiation, particularly 180–200 Gy, as effective for generating genetic variability in P. erosus to support future breeding of high-yield, semi-dwarf lines.