Study of sources and inheritance of resistance to African rice gall midge (Orseolia oryzivora) in lowland rice in Uganda
Belete, Desta Abebe
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The African Rice Gall Midge (AfRGM), Orseolia oryzivora is one of the major insect pests in Africa including Uganda. Yield losses of up to 100% are attributed to the AfRGM in different rice growing regions especially in lowland and irrigated. Some sources of resistance to AfRGM have to be developed in West Africa but none of the varieties grown in Uganda is resistant and information on mode of inheritance for AfRGM resistance is very limited for Ugandan rice genotypes. The objectives of this study were to identifying genotypes with resistance to AfRGM for introgression in Uganda locally adapted but susceptible genotypes and determination the mode of inheritance for AfRGM resistance. Twenty collected genotypes were evaluated in both field and cage experiments in randomized complete block design with three replications. Results showed highly significant differences (P<0.001) in genotypic reaction against AfRGM indicating high genetic diversity among the tested genotypes. Tillers number, percentage hill infestation and tillers damage, number of gall midge and galls, days to flowering and grain yield were highly variable among genotypes. Overall, four genotypes: NERICA-6, NERICA-4, NERICA-1 and METP-7 consistently showed resistance in both cage and field evaluations. Therefore, these genotypes were identified as potential sources of AfRGM resistance that could be utilized in the Uganda rice breeding programme to introgress AfRGM resistance into susceptible local rice varieties. Four resistant genotypes from the screening results and four susceptible locally adapted genotypes were crossed in half diallel crossing design. The F2 segregants and their corresponding parents were evaluated in the cage experiment against AfRGM in 4 by 9 alpha lattice design in three replications. These results showed that there was significant variation (P<0.001) for rice AfRGM resistance among genotypes. Significant general and specific combining abilities were observed, indicating that both additive and non-additive gene effects were important for rice AfRGM resistance, although the non-additive effects were predominant at 42 and 63 DAI. High coefficients of genetic determination in the broad sense (0.96, 0.97, and 0.98) and moderate narrow sense (0.55, 0.45, and 0.39) at 21, 42, and 63 DAI, respectively, were obtained on a genotype mean basis with a moderate Baker’s ratio of 0.57, 0.46 and 0.40 in the three cases respectively, indicating primarily non-additive inheritance among crosses except at 21 DAI.