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Kevin M. Crosby

Improving melon root systems by traditional breeding is one component of the program to develop multiple-stress-resistant melons at the Texas Agricultural Experiment Station, Weslaco. Ten diverse melon lines representing four horticultural groups were intercrossed utilizing a Design II mating scheme. The male parents were: `PI 403994,' `Perlita,' `Doublon,' `Caravelle', and `PI 525106.' The female parents were: `Créme de Menthe,' `Magnum 45,' `BSK,' `PI 124111 × TDI', and `Deltex.' F1 progeny were grown in pasteurized sand in the greenhouse using a randomized complete-block design with four reps. After 4 weeks, root systems from all plants were carefully washed to remove the sand. Each root system was then placed onto a glass, plated, and scanned into the computer software Rhizo Pro 3.8 (Regent Instruments, Quebec). This software calculated root lengths of various diameter classes, root area, and root tip number. All data was input into Agrobase software for calculation of genetic variances based on Design II analysis. Significant differences of contributions by male parents to progeny variation were few. Only length of roots with 1.0- to 1.5-mm-diameter and vine length were significantly different. Differences in contributions by female parents to all traits except root tip number were highly significant. No significant interaction effects were observed for any trait. Narrow-sense heritability estimates were moderate to high for all traits. The range was from 0.56 for root tip number by males to 0.81 for both length of 0.5- to 1.0-mm-diameter roots and vine length for females. Estimates for total root length (0.76) and root surface area (0.77) were high. The lack of male by female interaction suggests very low dominance genetic variation and contributed to high heritability estimates, which represent predominantly additive gene action. Additive genetic variation allows more-efficient progress by selection, making the potential for root system improvement favorable.

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Soon O. Park* and Kevin M. Crosby

Mature fruit size and shape are important traits of most melon types. Our objective was to identify RAPD markers associated with major QTL affecting fruit weight, length, diameter and shape by means of bulked segregant analysis in an F2 population from the ananas melon cross of Deltex (larger fruit size) × TGR1551 (smaller fruit size). Clear separations for fruit weight, length, diameter, and shape between Deltex and TGR1551 were observed. Continuous distributions for fruit weight, length, diameter and shape were found in the F2 population indicating quantitative inheritance for the fruit traits. Significant positive correlations were detected between fruit weight and shape traits (r = 0.73 to 0.80). A significant positive correlation was observed between fruit weight and glucose (r = 0.35) or fructose (r = 0.25), whereas no correlation was noted between fruit weight and sucrose or total soluble solids. Two small and large bulks for fruit weight and shape were developed from F2 plants. A total of 240 primers were used to simultaneously screen between the small and large bulks, and between Deltex and TGR1551. Twenty-six RAPD markers were polymorphic for the small and large bulks. Ten markers were found to be significantly and consistently associated with fruit size and shape traits on the basis of simple linear regression. Of the 10 markers associated, four displayed an amplified DNA fragment in the small bulk, while six showed an amplified DNA fragment in the large bulk. The associated marker OJ07.350 explained 15% to 27% of the phenotypic variation for the fruit traits. These markers associated with QTL for melon fruit size and shape are expected to be useful in melon breeding programs for modifying fruit size.

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Gene E. Lester and Kevin M. Crosby

Two important chemicals and an essential mineral (phytonutrients) for human health and well-being are ascorbic acid, 5-methyl-tetrahydrofolic acid (folic acid) and potassium. The influence of cultivar, fruit size, soil type and year on these compounds in [Cucumis melo L. (Inodorous Group)] was determined. Fully mature (abscised) commercial size fruit: 4, 5, 6, 8, and 9 (fruit/0.031 m3 shipping box) from three commercial cultivars: Mega Brew, Morning Ice, and TAM Dew Improved (TDI); and one experimental hybrid `TDI' × `Green Ice' were grown on both clay loam and sandy loam soils. Total ascorbic acid and folic acid content increased with an increase in fruit size up to a maximum (size 6 or 5), then decreased with further fruit size increase. Total ascorbic acid and folic acid content for most fruit sizes were higher when grown on clay loam versus sandy loam soils. The experimental hybrid compared to the commercial cultivars contained generally higher total ascorbic acid levels and significantly higher folic acid levels regardless of fruit size or soil type. Free ascorbic acid and dehydroascorbic acid contents were generally higher from clay loam versus sandy loam soils and in the experimental line versus the commercial cultivars. However, free ascorbic acid content was high in small fruit and remained unchanged with an increase in fruit size until size 6 or 5 then significantly decreased; while dehydroascorbic acid content linearly increased with an increase in fruit size. Potassium content averaged 1.7 mg·g-1 fresh weight for each line and did not significantly differ due to fruit size, but did for soil type and year. Analyses of variance for the phytonutrients assayed demonstrated that cultivar (genetics) always was very highly significant (P = 0.001), whereas, soil and year (environment) were not.

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Kevin M. Crosby, Daniel I. Leskovar and Kil Sun Yoo

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Alexandra B. Napier, Kevin M. Crosby and Soon O. Park

Muskmelons (Cucumis melo L.) play an important role in the American diet. Ranked as one of the top 10 most-consumed fruits by the USDA, cantaloupe melons have the highest amount of beta-carotene of all the ranked fruits. Beta-carotene, also called pro-Vitamin A, is an essential nutrient required for eye health, and may have the potential, as an antioxidant to reduce the risks associated with cancer, heart disease, and other illnesses. Breeding melons with increased levels of beta-carotene will benefit consumer health. Research has found phytonutrients are most bioavailable when consumed in their fresh form, rather than as vitamin supplements. The high level of beta-carotene found in some melons has a genotypic component, which may be exploited to breed melons high in beta-carotene. Molecular markers and marker-assisted selection (MAS) can be used to increase the efficacy of the breeding process, while lowering breeding costs. An F2 population was created using `Sunrise', the female parent, containing no beta-carotene crossed with `TAM Uvalde', a high beta-carotene variety. A field population consisting of 115 F2 individuals and a greenhouse population containing 90 F2 individuals were grown. The resulting fruit were screened phenotypically and ranked according to beta-carotene content. Chisquare values fit the previously reported model of a single dominant gene for presence of beta-carotene (orange-flesh) vs. absence (green or white flesh). A continuous distribution of beta-carotene concentrations from high to low suggested quantitative inheritance for this trait. Two eight-plant DNA bulks composed of either high or low beta-carotene F2 individuals were screened for polymorphic molecular markers using the amplified fragment-length polymorphism technique.

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Kevin M. Crosby, Daniel Leskovar, John L. Jifon and Joseph Masabni

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Soon O. Park, Hye Y. Hwang and Kevin M. Crosby

Our objectives were to construct a randomly amplified polymorphic DNA (RAPD) marker-based linkage map using an F2 population derived from the melon (Cucumis melo) cross of ‘Deltex’ × TGR 1551, and map quantitative trait loci (QTL) for sucrose, total soluble solids (TSS), ratio of sucrose to total sugars (RSTS), and ascorbic acid as well as the ms-3 locus for male sterility previously reported in other muskmelon crosses. Due to the dominant character of RAPD markers, we scored 192 ‘Deltex’- and 158 TGR 1551-derived markers. One hundred eighty (94%) of the 192 markers fit the expected 3:1 ratio. On the basis of the 180 markers, we constructed a ‘Deltex’ linkage map of 171 markers distributed on 12 linkage groups (LGs) with a total map distance of 1182 cM. One hundred fifty (95%) of the 158 markers were identified to be nondistorted. We developed a TGR 1551 linkage map of 138 markers distributed on 12 LGs with a total distance of 1163 cM. A combined map of 12 LGs with a total map distance of 1394 cM was made from 82 marker pairs expressing codominance. Nine LGs were integrated into those of the existing composite map by 17 anchor markers. We mapped the ms-3 locus for male sterility on LG 9, which corresponds to LG 10 of the classical map and LG VII of the composite map. Six QTL for sucrose were located on LGs 2, 3, 4, 6, and 11. Three on LGs 3, 4, and 6 and four on LGs 2, 3, 6, and 11 of the six QTL for sucrose were also noted to be QTL for TSS and RSTS, respectively. A single QTL for ascorbic acid was placed on LG 5. This map will also be used to identify QTL for fruit sweetness, quality, size, and shape traits, as well as disease resistance.

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Kevin M. Crosby, Daniel I. Leskovar and Kil Sun Yoo

At the Vegetable and Fruit Improvement Center, plant breeding has produced pepper lines with enhanced beneficial phytochemical levels. TAM `Dulcito' is a new jalapeño cultivar with no detectable levels of capsaicin, but increased levels of lutein. In greenhouse cultivation, it contained 122 ppm of this important human health-related compound, which aids in prevention of macular degeneration. This is a significant improvement over popular cultivars, such as `Grande', which contained 25 ppm or less. In addition to improved lutein levels, `Dulcito' also possesses resistance to three important potyviruses: TEV, PepMoV, and PVY. In field trials at Weslaco, Texas, `Dulcito' outyielded both TAM `Mild Jalapeño 2', and `Mitla'. This new cultivar produces a concentrated set of large, thick-fleshed fruit with few cuticular cracks. Because of its lack of pungency, it should be useful for the processing industry. TAM `Tropic Bell' is a medium-sized, blocky bell with enhanced levels of both ascorbic acid and lutein compared to other cultivars. Grown under greenhouse conditions, it contained 100 ppm lutein compared to 6 ppm in `Jupiter'. It also contained 660 ppm ascorbic acid at the green stage, compared to less than 100 ppm for three commercial bell cultivars tested. `Tropic Bell' produced yields equal to both `Valiant' and `Summer Sweet' commercial hybrids at Weslaco. Fruit of `Tropic Bell' were slightly smaller than the hybrid cultivars. TAM `Tropic Bell' possesses resistance to the same three potyviruses as `Dulcito' and demonstrated excellent tolerance to Phytophthora capsici in a controlled inoculation. These two new cultivars will be useful for production in locations with high potyvirus pressure or as specialty market items for health-conscious consumers.