A genetic analysis of banana resistance to weevils (cosmopolites Sordidus germar)
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Banana weevils (Cosmopolites sordidus Germar) are a very important pest contributing to the decline in banana production of up to 50% - 100% after the 3rdratoon cycle. East African highland cooking bananas are an important staple crop in the Great Lakes region of Eastern and Central Africa. However, they are highly susceptible to banana weevil. The objective of this study was to determine the inheritance of banana resistance to weevils and to identify and map quantitative trait loci (QTL) associated with weevil resistance traits in banana. This was done to help in determining the breeding method and in developing molecular markers for use in selection for weevil resistance breeding. F1 progenies from crosses of two banana types; Monyet (resistant tetraploid) and Kokopo (susceptible diploid) developed by the International Institute of Tropical Agriculture were screened for segregation for banana resistance to weevils in a pot experiment. There was a significant difference at P<0.001 among the genotypes for peripheral damage, outer cross-sectional damage, inner cross-sectional damage, and total cross-sectional damage, indicating that the population was segregating for resistance to banana weevils. Broad sense heritability values for total cross-sectional damage, outer cross-sectional damage and inner cross-sectional damage were 0.40, 0.34 and 0.41 respectively, which were moderately high, indicated that a moderate percentage of the variation amongst the genotypes was due to genetic factors. However, peripheral damage had lower broad sense heritability values of 0.26. There were also strong significant positive correlations amongst total cross-sectional damage, outer cross-sectional, inner cross-sectional and peripheral damage parameters. The quantitative QTL mapping identified four QTL for both peripheral damage and total cross-sectional damage. The QTL that were significant for peripheral damage were located on chromosomes 6, 7 and 11. Two QTL on chromosome 6 were identified for total cross-section damage. Quantitative mapping also identified 65 loci significantly associated with peripheral damage and 8 loci significantly associated with total cross-sectional damage. These loci can be used to develop molecular markers for selecting for banana resistance to weevils.