Phenotypic and nutritional diversity of indigenous rice (Oryza sativa L.) cultivars from Sikkim, India

Sikkim is an important repository of rice genetic diversity in India, owing to numerous indigenous cultivars adapted to diverse terrains and extreme climatic conditions. However, limited scientific characterization has constrained their effective utilization in crop improvement and breeding programs. In this study, 65 indigenous rice cultivars were evaluated to assess phenotypic, nutritional, and genetic variability across 22 key agronomic and grain-quality traits. Using standardized field management and laboratory protocols, data were analysed through one-way ANOVA, principal component analysis, and estimates of phenotypic variance (σ²P), genotypic variance (σ²G), broad-sense heritability (h²), and genetic advance as a percentage of the mean (GAM). Significant variation (p < 0.05) was observed for all measured traits. Doodhkatey and Japani exhibited the longest grains (10.60 mm), whereas Panbhara recorded the highest thousand-seed weight (29.70 g). Cooking-quality attributes varied considerably, with Japani showing the highest elongation index (2.19), and 49 cultivars displaying desirable low gelatinization temperatures. Amylose content ranged from 13.85% to 28.25%, with most cultivars classified as low (53.80%) or intermediate (41.50%) in amylose. Nutritional profiling revealed substantial diversity, with Doodhkatey showing the highest protein content (11.30%) and Ram Jeera the highest energy value (369.40 kcal/g). Manganese (Mn) was the most abundant mineral, ranging from 1.73 to 4.87 mg/100 g. Genetic analysis indicated high broad-sense heritability for key grain-quality traits, particularly elongation ratio (85.70%) and kernel length-to-breadth ratio (75.70%). These, combined with high GAM values (e.g., kernel L/B ratio, 53.00%; Mn, 46.80%), suggest strong additive gene action and the suitability of these traits for direct selection. Overall, the extensive genetic and nutritional diversity identified among the indigenous rice cultivars of Sikkim underscores their value for targeted breeding initiatives and for strengthening gene bank conservation strategies in the Eastern Himalayas.