Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 11, 2013
Publication Date: N/A
Interpretive Summary: Growers offering high quality watermelons that are also high in phytonutrients will have stronger market opportunities. In order to offer highly nutritious fruit, the industry must understand the nature of phytonutrient accumulation as it is affected by ploidy. This is especially true for the U.S. market where the majority of watermelons sold are seedless triploids.
Technical Abstract: Growers offering high quality watermelons [Citrullus lanatus (Thumb.), Matsum & Nakai] that are also high in phytonutrients will have stronger market opportunities. In order to offer highly nutritious fruit, the industry must understand the nature of phytonutrient accumulation as it is affected by ploidy. This is especially true for the U.S. market where the majority of watermelons sold are seedless triploids. The present study was performed on six field-grown watermelon diploid (2n) inbred lines, their induced autotetraploids (4n), and autotriploids (3n) to determine the importance of ploidy on quality and nutritional concentration. Lycopene, total soluble solids (TSS), L-citrulline (citrulline), glutathione (GSH), weight, width, and length were measured in ripe heart tissue from fruit grown at one location. Of the four traits we analyzed that did not have a family by ploidy interaction (citrulline, GSH, weight, and width), we determined the following: Citrulline levels were not significantly affected by ploidy in five out of six families, nor was there a significant correlation when all family's citrulline values were averaged. GSH was higher in autotriploid than in diploid or autotetraploid (95.0 vs. 66.9 or 66.7 µg•g-1 GSH, respectively); additionally, we found a positive association of GSH with fruit size. Of the three traits we analyzed that had a family by ploidy interaction (lycopene, TSS, and length), we determined the following: Within four of the families, ploidy affected lycopene concentration, but whether this interaction is positive or negative was family dependent. The mean TSS were higher in autotetraploid than in autotriploid, which was again higher than in diploid fruit averaged across families (10.5, 10.2, and 9.5% TSS respectively), there was a family x ploidy interaction so the significance of this increase is obviously affected by the family used to produce the triploid. Lycopene and TSS had a slight positive correlation. Four out of six families showed no statistical correlation between ploidy and length, and even though mean length across family demonstrated smaller tetraploid fruit, the family by ploidy interaction demonstrates that this observation is family dependant. Length and width correlate well with weight when combining data for all ploidy levels and when analyzing each ploidy separately. Length correlates more closely with width in autotriploid fruit than in diploid or autotetraploid fruit. These results highlight the importance of selecting diploid and tetraploid lines which promote triploids with good quality traits and phytonutrient concentrations.