PLOIDY MANIPULATIONS AND GENETIC-MARKERS AS TOOLS FOR ANALYSIS OF QUANTITATIVE TRAIT VARIATION IN PROGENY DERIVED FROM TRIPLOID PLANTAINS

Plantains (Musa spp. AAB group) are starchy bananas widely grown in Af rica and tropical America by small landholders. Genetic analysis of th e plantain genome is difficult due to its triploidy and high sterility . Ploidy manipulations (scaling up and down the number of chromosomes) and interspecific plantain-banana hybridization opened the path for t he genetic amelioration of the crop and for the investigation of its g enome for further manipulations. This report shows the associated effe cts of ploidy and of the major loci controlling vegetative fruit parth enocarpy and resistance to black sigatoka fungal leaf spot on growth a nd yield characteristics of plantain-banana euploid hybrids. The numbe r of copies of the black sigatoka resistance allele (bs(1)) and of the fruit parthenocarpy gene (P-1) in addition to their intralocus intera ction and ploidy level were all found to significantly affect bunch an d fruit characteristics in euploid plantain-banana hybrids. Epistasis significantly affected fruit weight and size in one cross but not in a nother. Significant multiple regression models combining ploidy and ge netic markers explained 15% to 85% of quantitative trait variation (QT V). The amount of QTV accounted by ploidy and genetic markers varied a ccording to the characteristic and cross in which the markers were exa mined.