Optimizing grass pea (Lathyrus sativus L.) for rice-fallow systems: phenotypic and genetic insights for dual-purpose breeding

Introduction Grass pea ( Lathyrus sativus L.), a resilient legume adapted to drought and waterlogged conditions, presents a promising solution for sustainable intensification of rice-fallow systems in South Asia, where ~9.7 million hectares remain uncultivated post-kharif due to moisture and socio-economic constraints. Materials and Methods This study evaluated seventeen diverse lines for dual-purpose (leaf and grain) utility, analysing morpho-agronomic traits, imbibition kinetics, and genetic diversity to identify optimal breeding material. Results Phenotypic characterization revealed significant variation: pulse-type genotypes flowered earlier (mean 47.1 ± 5.8 days) than leaf-types (54.4 ± 5.5 days), with plant height (12.33–43.66 cm), seed yield (1.98–3.34 g/plant), and leaf yield (28.76–60.71 g/plant) showing distinct trade-offs. Correlation analyses highlighted key associations, including strong negative relationships between days to flowering and seed yield ( r = −0.750) and between pod length and leaf yield ( r = −0.652). Imbibition kinetics varied genotypically, with fast-imbibing lines (e.g., Ratan) suited for rapid establishment in residual moisture, while slow-imbibing types (e.g., 75,049) showed potential for waterlogging resilience. Principal component analysis extracted 88.54% of variability into five components, with PC1 (42.23%) representing a yield–flowering time trade-off and PC2 (22.50%) separating broad-leaved from high-seed genotypes. Cluster analysis grouped genotypes into five distinct clusters, with maximum divergence between Clusters II and III (distance = 43.62), while solitary genotypes (Clusters IV–V) emerged as unique genetic resources. Discussion These findings provide a roadmap for breeding programs targeting rice-fallow adaptation, emphasizing early flowering for yield optimization, imbibition efficiency for moisture stress adaptation, and strategic utilization of genetically distant clusters (II × III) to maximize heterosis. The study underscores grass pea’s potential as a dual-purpose crop to enhance productivity and nutritional security in vulnerable rice-fallow systems.