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S. Jenni, D.C. Cloutier, G. Bourgeois, and K.A. Stewart

Plant dry weight of muskmelon transplants to anthesis could be predicted from a multiple linear regression based on air and soil temperatures prevailing under 11 mulch and rowcover combinations. The two dependent variables of the regression model consisted of a heat unit formula for air temperatures with a base temperature of 14C and a maximum-reduced threshold at 40C, and a standard growing-degree-day formula for soil temperatures with a base temperature of 12C. Based on 2 years of data, 86.5% of the variation in the dry weight (on a log scale) could be predicted with this model. The base temperature for predicting time to anthesis of muskmelon transplants was established at 6.8C and the thermal time ranged between 335 and 391 degree-days during the 2 years of the experiment.

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Gene E. Lester, Robert A. Saftner, and D. Mark Hodges

accumulation on melon fruit ( Cucumis melo L.) HortScience 41 1431 1434 Katz, D.A. 1998 Food additives: what they do 18 Dec. 2006 < http://www.chymist.com/Food%20Additives-What%20they%20do.pdf > Lester, G.E. 2006 Environmental regulation of human health

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Soon O. Park, Kevin M. Crosby, Rongfeng Huang, and T. Erik Mirkov

Male sterility is an important trait of melon in F1 hybrid seed production. Molecular markers linked to a male-sterile gene would be useful in transferring male sterility into fertile melon cultivars and breeding lines. However, markers linked to the ms-3 gene for male sterility present in melon have not been reported. Our objectives were to identify randomly amplified polymorphic DNA (RAPD) markers linked to the ms-3 gene controlling male sterility using bulked segregant analysis in an F2 population from the melon cross of line ms-3 (male-sterile) × `TAM Dulce' (male-fertile), convert the most tightly linked RAPD marker to the ms-3 gene into a sequence characterized amplified region (SCAR) marker based on a specific forward and reverse 20-mer primer pair, and confirm the linkage of the RAPD and SCAR markers with the ms-3 gene in an F2 population from the cross of line ms-3 × `Mission' (male-fertile). A single recessive gene controlling male sterility was found in F2 individuals and confirmed in F3 families. Two RAPD markers that displayed an amplified DNA fragment in the male-sterile bulk were detected to be linked to the ms-3 gene in the F2 population from the cross of line ms-3 × `TAM Dulce'. RAPD marker OAM08.650 was closely linked to the ms-3 gene at 2.1 cM. SCAR marker SOAM08.644 was developed on the basis of the specific primer pair designed from the sequence of the RAPD marker OAM08.650. The linked RAPD and SCAR markers were confirmed in the F2 population from the cross of line ms-3 × `Mission' to be consistently linked to the ms-3 gene at 5.2 cM. These markers were also present in 22 heterozygous fertile F1 plants having the ms-3 gene. The RAPD and SCAR markers linked to the ms-3 gene identified, and confirmed here could be utilized for backcrossing of male sterility into elite melon cultivars and lines for use as parents for F1 hybrid seed production.

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Hector G. Nunez-Palenius, Daniel J. Cantliffe, Harry J. Klee, and Don J. Huber

Pollen germination timing has a paramount role in fertilization of a flower. Rapid germination and outgrowth of a pollen tube that penetrates the stigma is required. Physical and biological factors can affect pollen germination timing. The objective of this study was to determine if ACC oxidase antisense gene expression could influence in vitro pollen germination and in vitro pollen tube length growth. A transgenic (ACC oxidase antisense) `Galia' male parental line had a reduced fruit set compared to its wild type. Likewise, embryo abortion and empty seeds after self-pollination in a `Galia' male parental line were observed. Wild type and transgenic `Galia' male parental line melon plants were grown in a greenhouse according to the practices of Rodriguez (2003). Male flowers were collected from these plants between 10 to 12 am; pollen was obtained by dipping the anther in germination medium (10.25% sucrose, 0.031% calcium nitrate, 0.015% boric acid, 0.0075% KNO3, and 0.016% MgSO4) at 25 °C and analyzed immediately, either for total percentage of germination after 5 minutes of incubation or to measure pollen tube growth rate every 5 minutes during 1 hour. Each flower provided an average of 250 pollen grains. Assays were conducted by using the “Hanging Drop Method” (Okay and Ayfer, 1994). Percentage of pollen germination in WT `Galia' male parental line was greater than the transgenic line. Likewise, in vitro pollen tube growth in wild type `Galia' melon was greater than pollen from the transgenic line. Possibly the ACC oxidase antisense gene expression in `Galia' male parental line may have had an influence on the reduced fruit set observed.

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Carol Gonsalves, Baodi Xue, Marcela Yepes, Marc Fuchs, Kaishu Ling, Shigetou Namba, Paula Chee, Jerry L. Slightom, and Dennis Gonsalves

A single regeneration procedure using cotyledon explants effectively regenerated five commercially grown muskmelon cultivars. This regeneration scheme was used to facilitate gene transfers using either Agrobacterium tumefaciens (using `Burpee Hybrid' and `Hales Best Jumbo') or microprojectile bombardment (using `Topmark') methods. In both cases, the transferred genes were from the T-DNA region of the binary vector plasmid pGA482GG/cp cucumber mosaic virus-white leaf strain (CMV-WL), which contains genes that encode neomycin phosphotransferase II (NPT II), β-glucuronidase (GUS), and the CMV-WL coat protein (CP). Explants treated with pGA482GG/cpCMV-WL regenerated shoots on Murashige and Skoog medium containing 4.4 μm 6-benzylaminopurine (BA), kanamycin (Km) at 150 mg·liter-1 and carbenicillin (Cb) at 500 mg·liter-1. Our comparison of A. tumefaciens- and microprojectile-mediated gene transfer procedures shows that both methods effectively produce nearly the same percentage of transgenic plants. R0 plants were first tested for GUS or NPT II expression, then the polymerase chain reaction (PCR) and other tests were used to verify the transfer of the NPT II, GUS, and CMV-WL CP genes. This analysis showed that plants transformed by A. tumefaciens contained all three genes, although co-transferring the genes into bombarded plants was not always successful. R1 plants were challenge inoculated with CMV-FNY, a destructive strain of CMV found in New York. Resistance levels varied according to the different transformed genotypes. Somaclonal variation was observed in a significant number of R0 transgenic plants. Flow cytometry analysis of leaf tissue revealed that a significant number of transgenic plants were tetraploid or mixoploid, whereas the commercial nontransformed cultivars were diploid. In a study of young, germinated cotyledons, however, a mixture of diploid, tetraploid, and octoploid cells were found at the shoot regeneration sites.

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Jack E. Staub, James D. McCreight, and Juan E. Zalapa

Genes residing in highly branched, fractal melons [ Cucumis melo ssp. agrestis (Naud.) Pangalo] have the potential for increasing yield in dessert melon types, C. melo L. ssp. melo ( Zalapa et al., 2006 ). A horticulturally unique C. melo

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Gabriele Gusmini and Todd C. Wehner

Yield data for the major cucurbit crops in the United States have been collected and summarized. Yield trends are presented for cucumber (Cucumis sativus; processing and fresh-market), melon (Cucumis melo; muskmelon and honeydew), and watermelon (Citrullus lanatus) for the period 1951–2005. Data have been obtained from the U.S. Department of Agriculture, as originally reported by six of its units: Agricultural Marketing Service, Agricultural Research Service, Bureau of Agricultural Economics, Economic Statistics Service, National Agricultural Statistics Service, and Statistical Reporting Service. For all crops yields have been increasing over time, except for processing cucumber, for which yields seem to have reached a plateau by the end of the 1990s.

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Wenjing Guan and Xin Zhao

Grafting has been used for controlling certain soilborne diseases and improving abiotic stress tolerance in muskmelon (Cucumis melo) production. Grafting methods may vary considerably among geographic regions and nurseries, while excision of rootstock roots before graft healing may also be practiced, which allows root regeneration of the grafted plants. In this greenhouse study, four grafting methods including hole insertion, one-cotyledon, noncotyledon, and tongue approach methods were examined for their impacts on plant growth and root characteristics of ‘Athena’ muskmelon grafted onto ‘Strong Tosa’ interspecific hybrid squash rootstock (Cucurbita maxima × C. moschata). Nongrafted rootstock and scion plants were included as controls. Both the grafted and nongrafted plants were examined with or without root excision. The practice of root excision was unsuccessful with the tongue approach method, while it did not exhibit significant effects on graft quality and growth of plants grafted with the one-cotyledon and hole insertion methods. Grafted plants with root excision started to show active and rapid root regeneration at 8 days after grafting (DAG) and reached similar root length and surface area as the root-intact plants at 16 DAG. Plants grafted with the noncotyledon method showed a different root growth pattern with decreased root length and surface area at 16 DAG. As a result, this method reduced the quality of grafted plants. No significant differences in plant growth characteristics were observed among the hole insertion, one-cotyledon, and tongue approach grafted plants.

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Menahem Edelstein and Haim Nerson

. Wodner, M. Kigel, J. 1995a Role of endogenous gibberellins in germination of melon (Cucumis melo) seeds Physiol. Plant. 95 113 119 Edelstein, M. Bradford, K.J. Burger, D.W. 2001 Metabolic

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Shinsuke Agehara and Daniel I. Leskovar

Excess transpiration relative to water uptake often causes water stress in transplanted vegetable seedlings. Abscisic acid (ABA) can limit transpirational water loss by inducing stomatal closure and inhibiting leaf expansion. We examined the concentration effect of exogenous ABA on growth and physiology of muskmelon (Cucumis melo L.) seedlings during water stress and rehydration. Plants were treated with seven concentrations of ABA (0, 0.24, 0.47, 0.95, 1.89, 3.78, and 7.57 mm) and subjected to 4-day water withholding. Application of ABA improved the maintenance of leaf water potential and relative water content, while reducing electrolyte leakage. These effects were linear or exponential to ABA concentration and maximized at 7.57 mm. Gas-exchange measurements provided evidence that such stress control is attributed to ABA-induced stomatal closure. First, net CO2 assimilation rate and stomatal conductance initially decreased with increasing ABA concentration by up to 95% and 70%, respectively. A follow-up study (≤1.89 mm ABA) confirmed this result with or without water stress and further revealed a close positive correlation between intercellular CO2 concentration and net CO2 assimilation rate 1 day after treatment (r 2 > 0.83). In contrast, ABA did not affect leaf elongation, indicating that stress alleviation was not mediated by leaf area adjustment. After 18 days of post-stress daily irrigation, dry matter accumulation showed a quadratic concentration-response, increasing up to 1.89 mm by 38% and 44% in shoot and roots, respectively, followed by 16% to 18% decreases at >1.89 mm ABA. These results suggest that excess levels of ABA delay post-stress growth, despite the positive effect on the maintenance of water status and membrane integrity. Another negative side effect was chlorosis, which accelerated linearly with increasing ABA concentration, although it was reversible upon re-watering. The optimal application rate of ABA should minimize these negative effects, while keeping plant water stress to an acceptable level.