Genetic Analysis and Combining Ability on Spikelet Fertility Related to Cold Tolerance in Japonica Rice

Each parent, P₁ and P₂, ten F₁ hybrids among 5 parents, eight F₂, B₁ (F₁ × P₁), and B₂ (F₁ × P₂) derived from 8 crosses were evaluated for spikelet fertility related to cold tolerance in cold-water irrigated plot. Heterosis for spikelet fertility varied from −8.6% to 60.5% with a mean of 20.6% and showed positive effects in all crosses except for Sambagbyeo/Stejaree 45, indicating that the gene effect is partial dominant. Heterobeltiosis ranged from −22.9% to 25.5% with a mean of −1.6%. Three hybrids of Unbong 31/Sambaegbyeo, Sambaegbyeo/HR19621-AC6, and Hitomebore/Stejaree45 had higher fertility than the superior parents, indicating over-dominance. Both general combining ability (GCA) and specific combining ability (SCA) were highly significant for spikelet fertility. The variance of GCA effect was larger than that of SCA effect, indicating that variance components due to additive effects might be larger than those due to non-additive effects for this character. Analysis of genetic parameters for the 5 × 5 half-diallel F₁s, revealed that spikelet fertility fitted to the additive-dominance model. Broad-sense heritability (h₂B) was higher than narrow-sense heritability (h₂N). Cold tolerance by the result of the frequency distribution of 8 crosses was a quantitative character expressed by polygene. The genetic mode for spikelet fertility using the joint scaling test was shown to be additive, dominance, and additive-dominance gene effects. Additive gene effect was higher than dominance gene effect.