Genetic Variability, Heritability, and Trait Associations in Rice Genotypes under Low Nitrogen Conditions

Abstract

Nitrogen is a primary macronutrient required for rice growth and development. The present study evaluated sixty rice genotypes across two seasons under low-nitrogen conditions. Mixed-model ANOVA indicated significant genetic variability for all evaluated agronomic traits. To rigorously account for environmental variation, best linear unbiased prediction (BLUP) estimates were derived using a mixed linear model framework. This approach applies shrinkage towards the population mean, thereby reducing the inflation of extreme values and isolating stable genotypic effects. High heritability in conjunction with high genetic advance was recorded for 100-seed weight, total and filled grains panicle-1, biological yield, and grain yield, indicating the predominance of additive gene effects. Grain yield demonstrated stable genetic control, establishing it as a reliable selection criterion. BLUP-based ranking identified RPR-6 (4.16), MS15 (3.03), MS22 (2.24), Rasi (2.06), and RPR-4 (1.72) as superior, stable genotypes across seasons. Specifically, RPR-6 and MS15 exhibited coordinated improvements in sink strength and biological yield, while MS22 and Rasi demonstrated highly efficient biomass partitioning. Correlation analysis revealed strong positive associations between grain yield and biological yield, while a significant negative correlation existed between biological yield and harvest index. Cluster analysis grouped genotypes into distinct clusters, identifying Cluster 2 as a source of high-yielding lines. Ultimately, this exploitable variability will provide a valuable foundation for breeding rice cultivars adapted to a low-nitrogen environment.