Trait-Specific Heterosis and Inbreeding Depression Patterns in Rice: Implications for Hybrid Breeding

Abstract

Background Information: Understanding the magnitude and direction of heterosis and inbreeding depression for yield and its component traits is critical for designing effective hybrid breeding strategies in rice (Oryza sativa L.). Trait-specific analysis provides valuable insights into the genetic control of performance and stability across generations, enabling breeders to identify promising parental combinations and optimize selection methods. Methodology: The study was conducted during summer 2025 at the Regional Rice Research Station, NAU, Vyara, using five generations (P₁, P₂, F₁, F₂, and F₃) of four rice crosses: NVSR 3169 × Gontra Bidhan 3, NVSR 3169 × Pusa 1509, Lal Kada Gold × DRR Dhan 62 and Lal Kada Gold × IR 55179-3B-11-3. A Compact Family Block Design with three replications was adopted. Observations were recorded on thirteen agronomic and grain quality traits and estimates of relative heterosis, heterobeltiosis, and inbreeding depression were computed for each cross-trait combination using standard biometrical procedures. Results: Significant differences among generations for all traits confirmed substantial genetic variability. Positive and significant relative heterosis for grain yield per plant, straw yield, productive tillers per plant, and 100-grain weight was observed in most crosses, with Crosses II, III, and IV exhibiting >30% relative heterosis for grain yield. Cross-I expressed desirable negative heterosis for days to flowering and maturity, indicating potential for earliness. Significant positive heterobeltiosis for grain yield and associated traits was recorded in Crosses III and IV, whereas Cross I showed desirable negative heterobeltiosis for plant height and flowering traits. Inbreeding depression was highest in Cross II for grain yield (49.33%) and straw yield (32.28%), indicating strong non-additive gene effects, while Cross I displayed desirable negative inbreeding depression for plant height, flowering, and maturity. The cross–trait patterns indicated that traits with high heterosis and high inbreeding depression are predominantly governed by non-additive gene action, favoring hybrid breeding, whereas traits with lower inbreeding depression and higher heritability are amenable to early generation selection.