Weed competitiveness and yielding ability of aerobic rice genotypes

Keywords:    Broad-sense heritability; Crop vigour; Genetic correlation; Indirect selection index; Plant erectness; Rice germplasm; Seeding rate; Vegetative growth; Weed-suppressive ability.Aerobic rice, grown under aerobic soil conditions like maize or wheat, is an innovative way to cope with the growing demand for rice and the increasing water scarcity. Weeds are the most severe constraint to aerobic rice. The use of herbicides causes environmental pollution and induces the proliferation of resistant weed biotypes. These risks and the costs of labor for weeding prompt research on environment-friendly and labour-efficient methods of weed control. The adoption of weed-competitive genotypes is regarded as an effective tool in integrated weed management. The main objectives of this study were to explore the feasibility of breeding for weed competitiveness, to develop an indirect selection index for the trait, and to test the efficacy of a weed-competitive genotype in weed management.Field experiments were carried out at the International Rice Research Institute in the Philippines. Aerobic and upland genotypes were grown under aerobic conditions to study their performance under both weed-free and weedy environments.A large genetic variability within Oryza sativa both in weed-suppressive ability (WSA) and yielding ability under weed competition was detected. These two traits were moderately heritable and closely associated. Yield and early crop vigour investigated under weed-free conditions accounted for 87% of genotypic variation in yield under weed competition and for 40% of the variation in weed biomass; thus, weed-free yield and early crop vigour should both be included in an indirect selection index for breeding high-yielding, weed-competitive genotypes. Fast early vegetative growth rather than plant erectness was crucial to strong WSA.Indicagermplasm in both yielding ability and WSA, and aus germplasm in WSA were both superior to tropical japonica germplasm and the progenies of indica /tropical japonica ; thus, indica and aus germplasm may be used as gene donors for breeding for strong WSA in the tropics. The effects of genotype and seeding rate on suppressing weeds were additive; it was shown that a strongly weed-competitive genotype at an appropriate seeding rate (300 viable seeds m-2) suppresses weeds effectively. These findings indicate that weed-competitive genotypes may contribute greatly to weed management in aerobic rice agro-ecosystems.