Molecular Mapping of RAPD Markers and Andromonoecious Associated with QTL for Days to Harvest In Ananas Melon

Our objective was to identify RAPD and floral markers associated with QTL for days to harvest in a genetic linkage map recently constructed with an F2 population from the melon cross of Deltex (early maturity) x TGR1551 (late maturity) grown in a greenhouse. Marker-QTL associations would then be confirmed for this trait in an F2 population from the same cross in a field. Previously, we mapped QTL for fruit size and shape, seed size and quantity, sugars, and disease resistance on the linkage map. Thus, our additional goal was to determine the relationship between these newly identified QTL and the previously mapped QTL for the traits. A continuous distribution for days to harvest was found in the populations indicating quantitative inheritance for the trait. We noted positive correlations of days to harvest with other fruit size and quality traits including fruit weight, flesh weight, seed cavity weight, total soluble solids, and glucose. Nine RAPD markers, located on linkage groups 1, 4, 6, and 10 of the Deltex map, were detected to be significantly associated with QTL for days to harvest in the F2 population in the greenhouse based on simple linear regression. Six unlinked markers on the Deltex map explaining 30% of the total variation for the trait were significant in a stepwise multiple regression analysis. Eleven RAPD and andromonoecious markers on linkage groups 3, 4, 5, 6, and 10 of the TGR1551 map were significantly associated with QTL for days to harvest in the greenhouse population. Six TGR1551-derived markers, including andromonoecious, were significant in the stepwise multiple regression analysis, and explained 44% of the total variation for days to harvest. Of the 20 markers for days to harvest on six linkage groups of the map, 12 were consistently expressed in our populations under greenhouse and field environments. The andromonoecious locus on linkage group 4 was also associated with five fruit size and shape traits as well as five fruit sweetness traits. Two regions on linkage groups 6 and 10 for day to harvest were also associated with all comprehensive sugar traits and four fruit size and shape traits, respectively. These RAPD and floral markers mapped and confirmed here can be useful in breeding to develop different maturity class melon cultivars.