INHERITANCE OF HIGH-DENSITY GRAIN INDEX IN AN UPLAND RICE (ORYZA-SATIVA) CROSS

The components of gene effects for high-density grain index were studi ed in a cross 'Khaolo 33' x 'Kalinga III' of rice (Oryza sativa L.) fo llowing 5-parameter model of Hayman, utilizing means of P-1, P-2, F-1, F-2 and F-3 generations. The high-density grain index showed high het erobeltiosis along with high inbreeding depression, indicating the rol e of dominance gene action in the inheritance of this trait. The addit ive and dominance interactions were important, but this character was largely governed by non-additive gene action. Complementary epistasis was prevalent. The preponderance of dominance x dominance type of gene effect restricts the scope of early-generation selection. The progeny selection in F-3 or F-4 generation may be useful for the improvement of this character, whose association with grain weight, size and shape was not consistent in F-2 and F-3 generations.