QTL detection for fruit commercial quality traits in diploid and triploid banana populations
Desert bananas (Musa spp.) are a major fruit crop worldwide for which postharvest quality traits are major determinants for consumer acceptance and adoption of new cultivars. They are thus important targeted traits in breeding yet their genetic basis remains poorly characterized. We report the first QTL mapping study of two of these quality traits, finger drop resistance and bruising susceptibility, using two biparental populations sharing the same genetic background but differing in ploidy level: a diploid Pisang Madu × Galéo population and a triploid Pisang Madu T × Galéo population. For finger drop, heritability reached 0.47 in diploids and 0.38 in triploids. Two significant QTLs, q1_FD_M7-1 and q2_FD_M11, were detected in the diploid population and together explained 28.12% of the phenotypic variance. q1_FD_M7-1 was located in a non-recombining chromosomal region associated with a reciprocal translocation in Pisang Madu. Candidate genes co-localizing with finger drop QTLs included expansins, xyloglucan endotransglucosylases, and pectin methylesterases involved in cell wall remodeling. For bruising susceptibility, heritability was higher in triploids (0.57) than in diploids (0.48). One QTL and one putative QTL detected in the triploid population together explained 28.78% of the phenotypic variance. Cross-ploidy validation showed moderate predictive ability of QTL-based models between populations, with prediction accuracies of 0.52 for finger drop and 0.42 for bruising susceptibility. These QTLs are promising targets for marker-assisted selection to accelerate the development of new desert banana cultivars which are urgently needed to diversify the current production mainly based on monoculture of Cavendish.