Host-plant interactions and resistance mechanisms to banana weevil Cosmopolites sordidus (Germar) in Ugandan Musa germplasm

[摘要] English: Banana is an important subsistence crop in many tropical regions of the world. In the EastAfrican Great Lakes region it constitutes a staple food for more than 17 million people.Among many production constraints, banana weevil (Cosmopolites so rdidusi. is the mostserious pest to the crop. The tunnels caused by the boring larvae interfere with water andmineral uptake, and provide entry for fungi and bacteria. Most importantly this weakens thecorm, leading to toppling of plants even in slight winds. Host plant resistance is consideredthe basis of any successful integrated pest management plan, if the banana weevil problem isto be solved by the resource poor farmers.The screening trial of 45 Ugandan Musa germplasm accessions revealed that the plantainsubgroup (AAB) was most susceptible to banana weevil followed by East African highlandbanana clones. The exotic bananas, especially Kayinja, Bluggoe (ABB), Kisubi and Ndiizi(AB) were resistant to banana weevil. Plantain derived tetraploid hybrids of the wild bananaCalcutta-4 were also susceptible, indicating dosage effect of the susceptible gene.Mbwazirume, Tereza and Nakyetengu have been found to be relatively resistant local landraces and they are recommended as possible resistant selections. Total inner damage wasfound to be the best criteria for screening, and selecting for weevil resistance, since it scoredthe highest heritability and was highly correlated with all other weevil damage indices.Significant phenotypic and genotypic correlations were found between corm hardness, drymatter content, sap/resin production, suckering ability and corm size and banana weevildamage. These were therefore considered important mechanisms of resistance in Musa andthis indicated that banana weevil resistance is a complex polygenic trait.In agreement with the literature studied. antixenosis was not found to be important as aresistance mechanism in Musa. However. results from various no-choice experiments onhatchabil ity and development revealed significant differences. The previously observedresistance cultivars Kayinja. Yangambi-km5 and FHIA03, unlike the more susceptibleplantains and EAHBs, significantly increased developmental time and in some cases caused mortality of immature weevil stages.Preliminary studies on the influence of secondary metabolites were undertaken. The resultsshowed the presence of two or three compounds indicated by peaks on HPLC chromatogramsof methanol extracts of corms from resistant cultivars (e.g. Kayinja and FHIA03) that werenot present in susceptible cultivars (e.g. Atwalira and Gonja). These substances were also notpresent in some resistant cultivars like Yangambi-km5 and Cavendish, both of the AAAgenome group. This was yet another indication that resistance is complex and these differentfactors are important in different groups of cultivars.

[发布机构] University of the Free State