Gene action and standard heterosis over environments in Rice (Oryza sativa L.)
Keywords: Rice, Environment, gene action, heritability, standard heterosis
AbstractThe 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 ( ) 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 /4 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 ( / ) 1/2 was more than unity. The estimates of
/ 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 to28.29%, 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.
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