Inheritance of high-density grain index in an upland rice (Oryza sativa) cross

The components of gene effects for high-density grain index were studied in a cross 'Khaolo 33' x 'Kalinga III' of rice (Oryza sativa L.) following 5- parameter model of Hayman, utilizing means of P 1 , P 2 , F1, F 2 and F 3 generations. The high-density grain index showed high heterobeltiosis along with high inbreeding depression, indicating the role of dominance gene action in the inheritance of this trait. The additive 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.