Genetic Variability, Heritability and Genetic Advance for Yield and Yield-Attributing Traits in Rice (Oryza sativa L.) Under Phosphorus Deficiency

Phosphorus-deficient soils can limit rice performance, making the identification of selectable variation under low-phosphorus conditions important for breeding. The 38 recombinant inbred lines (RILs) of Improved Samba Mahsuri (ISM) × LR-299 and their two parents were evaluated as single, unreplicated plots in a four-block augmented design (Federer, 1956) at ICAR-Indian Institute of Rice Research, Rajendranagar, Hyderabad, Telangana, India, during Kharif 2024, under low-phosphorus field conditions, with four check varieties (Rasi, Swarna, ISM, DRR Dhan 60) repeated in every block to supply an independent error term. Block effects were estimated from the replicated checks and used to adjust test-entry values; analysis of variance was then carried out on the 40 block-adjusted entry means and tested against the check-derived error term. Genotypic and phenotypic coefficients of variation (GCV, PCV), broad-sense heritability (h²bs) and genetic advance as per cent of mean (GAM) were computed for days to 50% flowering (DFF), plant height (PH), number of tillers (NT), number of productive tillers (NPT), number of grains per panicle (NGP), spikelet fertility (SF) and grain yield per plant (GY). Entries differed significantly for DFF, PH, NGP and GY; NT and NPT did not differ significantly. PH, NGP and GY combined high heritability (91.65%, 91.97%, 65.72%) with high GAM (32.07%, 43.08%, 36.14%), identifying them as reliable, directly selectable criteria. Entries IX299-160-2, IX299-87-1, IX299-150 and IX299-177 recorded the highest block-adjusted grain yield among the 40 entries evaluated and are proposed as candidate donors for phosphorus-use-efficiency breeding. Plant height, grains per panicle and grain yield are governed predominantly by additive gene action in this population and are recommended as primary selection criteria for phosphorus use efficiency breeding, with the four identified entries advanced for further, replicated evaluation.