Gene action and standard heterosis over environments in Rice (Oryza sativa L.)

The present study on genetic components of variance carried over individual and pooled environments for thirteen metric traits in rice revealed the greater magnitude of dominance component than corresponding additive component of variance, thereby showing greater role of dominance in genetic control for most of the traits. The net dominance effect (ĥ2) was positively significant for the traits plant height, productive tillers per plant, spikelets per panicle, days to flowering and maturity. The estimate was non-significant for all the traits studied. The proportion of Ĥ2/4Ĥ1 was less than 0.25 for all the traits. The proportion of dominance and recessive alleles (KD/KR) in the parents was greater than one for majority of the traits suggesting preponderance of dominance alleles. The study on genetic ratios revealed that proportion of average degree of dominance measured from genetic components of variance was more than unity. The estimates of ĥ1/Ĥ2 were more than 0.50 for most of the characters. Low narrow sense heritability estimates were recorded for most of the traits. Thirteen cross combinations demonstrated the maximum manifestation of standard heterotic effect for grain yield plant−1 over check varieties Jhelum and Shalimar Rice-1. The magnitude of heterosis over Jhelum and Shalimar Rice-1 ranged from -56.07 to 35.21% and -62.69 to 28.29%, respectively. The most promising cross combinations for grain yield plant−1 in order of merit over standard checks Jhelum and Shalimar Rice-1 included SKAU-389 x K-08-60 (35.21 and 28.29%), Jhelum x K-08-60 (32.22 and 26.20%), SKAU-389 x Pusa Sugandh-5 (30.74 and 24.14%), Jhelum x SKAU-389 (29.07 and 22.58%) and China-988 x Shalimar Rice-1 (27.08 and 22.49%). Further, these crosses revealed high heterosis in desirable direction for other economically important traits.