The ratio of individual sugar compositions is an important fruit quality trait in muskmelon. Our objective was to identify RAPD markers associated with QTL for percentage of each individual sugar (sucrose, glucose, and fructose) using bulked segregant analysis in an F2 population derived from the melon cross of `TAM Dulce' (high sucrose percentage of total sugars) x TGR1551 (low sucrose percentage of total sugars). Continuous distributions for sucrose, glucose, and fructose percentages of total sugars were observed in the genetic population indicating quantitative inheritance for the traits. A significant positive correlation was observed between sucrose percentage and sucrose (r= 0.89) or soluble solids (r= 0.33), whereas a significant negative correlation was noted between sucrose percentage and glucose percentage (r = –0.85) or fructose percentage (r = –0.58). A total of 500 primers was used to screen between low and high DNA bulks for three individual sugar percentages. Ten RAPD markers, four amplified from `TAM Dulce' and six amplified from TGR1551, were significantly associated with QTL for at least one individual sugar percentage. Of the 10 markers identified, six were consistently associated with two to three traits. The OAU13.1350 obtained from `TAM Dulce' accounted for 13% and 19% of the phenotypic variation for sucrose and glucose percentages, while OAW06.600 obtained from TGR1551 explained 17% and 18% of the variation for the two traits. The OAA09.350 and OAU05.600 markers accounted for 4% to 13% of the variation for three sugar percentages. These markers associated with QTL for three individual sugar compositions could be useful in melon breeding for improving the mature fruit quality.
S. Park, J. Sinclair, K. Crosby, K. Yoo, and L. Pike
Carlos A. Lazcano, L.M. Pike, and K.S. Yoo
A new designer carrot, `BetaSweet', with high levels of anthocyanin, betacarotene, and crispy texture was developed by the Vegetable Improvement Center at Texas A&M Univ. The new carrot contained low levels of low-volatile terpenoids, responsible for the harsh flavor in carrots and high levels of reducing sugars. Carotenoid content increased with carrot maturity and stabilize at 120 days after sowing for orange and maroon genotypes; however, the maroon genotype was 35% higher than the orange cultivar. Anthocyanin, a cancer preventive compound and not detected in ordinary orange carrots, is present in `BetaSweet' maroon carrot with 89.8 mg·100 g-1 of fresh weight. High percentage of soluble solids and succulence in the maroon cultivar seemed to contribute to the favored sweetness perception by consumers. A consumer taste panel showed a significant difference between orange and maroon genotype for sweetness, texture, and overall carrot flavor.
J. Alcalá-Sáinz, K.S. Yoo, L.M. Pike, and R.W. Jones Jr.
Fifteen shortday onion cultivars grown at two production locations (GB and ST) in the Lower Rio Grande Valley, Texas were evaluated for pungency levels using gas chromatography (GC) and pyruvic acid tests.
Significant differences (P=0.05) were observed between cultivars in the pyruvic acid and GC tests within each location. Pyruvic acid content ranged from 3.0 to 5.1 μmol·g-1 fresh wt. The amount of total sulfur volatiles measured by the GC method ranged from 28 × 103 to 58 × 103EU. The correlation coefficients between GC and pyruvic acid were 0.10*** and 0.18*** at the GB and ST location, respectively.
When the two locations were combined, no significant differences (P=0.05) were observed between cultivars or locations using the GC test. However, the pyruvic acid test showed significant differences between locations. This result indicated that each cultivar had a different response in pungency as influenced by production location or environment.