The narrowing gap between commercial and experimental yields in irrigated rice (Oryza sativa L.) has renewed interest in genetic yieldimprovement. Evaluation of past gains is useful for identifying areas with potential for further enhancement. Tall rice cultivar Bluebonnet 50, introduced semidwarfs ‘IR8’ and ‘IR22’, and 13 semidwarfs developed locally from 1971 to 1989 were grown in Colombia under irrigation and rainfed conditions with and without blast (Pyricularia grisea, Sacc.) control during 1992 and 1993. The objective was to estimate progress from introduction and breeding of semidwarfs. Both types of semidwarfs yielded 80 and 122% more than Bluebonnet 50 under irrigation and rainfed conditions with blast control, respectively. Without blast control, the yield advantage (126%) was significant only in 1993. Tillering of semidwarfs was higher in all environments, ranging from 379 to 721 panicles per square meter versus 173 to 392 panicles per square meter for Bluebonnet 50. Panicles were smaller, ranging from 61 to 95 filled grains per panicle versus 118 to 187 filled grains per panicle for Bluebonnet 50. Mean grain yields of introduced and local semidwarfs were similar, but the latter were 10 to 15 cm taller. Linear regressions of means of local cultivars on year of release were nonsignificant (P > 0.05) for the irrigated and rainfed‐with‐blast control environments. For rainfed conditions without blast control, yield increased 0.13 ± 0.041 ba−1 yr−1; panicle size (1.1 ± 0.4 grains yr−1) and plant height (1.1 ± 0.2 cm yr−1) also increased. Breeding in Colombia has improved adaptation of semidwarf rice to rainfed environments.
The inheritance of resistance to mechanical damage in rice caused by sogata, Tagosodes orizicolus (Muir), was studied in cultivars with this resistance. Evaluation of F1 and F3 generations suggests that resistance to mechanical damage is controlled by a single dominant gene (A). This gene, present in cultivars Makalioka and Mudgo, is homozygous. The gene confers resistance, but its expression is modified by another gene (B). The action of the modifier gene is dependent on the genotype and the exposure to insect attack. For Mudgo, the modifier gene is in the homozygous form (bb), which accelerates the expression of the susceptible phenotype. In Makalioka, the dominant homozygous form (BB) retards the expression of susceptibility.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.