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Rita de C.S. Dias, Belén Picó, Javier Herraiz, Amparo Espinós, and Fernando Nuez

Vine decline is limiting muskmelon production in many growing areas. Monosporascus cannonballus Pollack and Uecker and Acremonium cucurbitacearum Alfaro-García, W. Gams, and J. García-Jiménez are the main causal agents of this disease in Spain. The wild accession Pat81 (Cucumis melo subsp. agrestis Jeffrey) has shown to be highly resistant in naturally infested fields and after artificial inoculations. In three greenhouse experiments conducted over two seasons, the root structure of Pat81 was examined and compared to the highly susceptible commercial cultivar Amarillo Canario (AC). Pat81 produced a more vigorous, branched, and longer root system, conferring to this accession a higher capacity for the uptake of water and nutrients, even after inoculation using naturally infested soil. To determine the plasticity of the root systems, the effect of five different soil substrates on root growth was assayed. The root morphology was highly influenced by the soil substrate. Differences between genotypes appeared at 10 weeks after transplanting using sand as soil substrate. An organic substrate made up of well-decomposed peat and sand minimized the genotype × substrate interactions, and facilitated root analysis. This substrate allowed bringing the sampling date forward to flowering (at 7 weeks after transplanting). The maximum root length, the number and size of lateral roots (diameter 0.5-1 mm) and branching order, consistently differed between the two genotypes in most of the assayed substrates. These easily measurable root traits can be used as selection criteria in healthy soils to breed a larger root system more tolerant to stress. In addition, in inoculated soils the greater root absorbent area and the reduced lesion intensity of Pat81 could have applications to increase vine decline resistance of cultivated melons. By using segregant populations derived from the cross AC × Pat81, we are trying to modify the root structure of muskmelon in order to offer a genetic alternative to the expensive strategy of grafting muskmelon varieties onto rootstocks resistant to soil stresses.

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Yasuyoshi Hayata, Xin-Xian Li, and Yutaka Osajima

An investigation was conducted to determine how pollination and CPPU treatment influence endogenous IAA and ABA content in netted muskmelon [Cucumis melo L. (Reticulatus Group) `Crest Earl's'], and to clarify their roles in fruit set and development in relation to these endogenous plant hormones. CPPU treatment at anthesis significantly increased the fresh weight of ovaries, whether the flowers were pollinated or not, but from 6 days after anthesis (DAA) the growth rate in the nonpollinated + CPPU treatment tended to be lower than the growth rates in the pollination treatment plots. Ovaries of nonpollinated flowers not treated with CPPU failed to grow and turned brown within 4 DAA. IAA content in the placenta of fruit from pollinated flowers increased rapidly from the day of anthesis to 2 DAA and remained at relatively high levels. IAA content in the placenta of parthenocarpic fruit induced to develop by CPPU treatment was lower than that of fruit from pollinated flowers but the pattern was almost the same as that in fruit of pollinated flowers. Conversely, IAA content in the placenta of fruit from nonpollinated flowers not treated with CPPU decreased sharply after anthesis. IAA content in the mesocarp of CPPU-treated fruit, whether or not the flowers were pollinated, increased significantly from the day of anthesis to 2 DAA, then decreased to almost the same level as that of the pollination-only treatment by 10 DAA, while the IAA content of nonpollinated CPPU-treated fruit declined even further. IAA content in the mesocarp of fruit from nonpollinated flowers not treated with CPPU decreased sharply. ABA contents in both the placenta and mesocarp of muskmelon that would set decreased after anthesis while the ABA content of muskmelon that would not set increased rapidly. Results suggest that pollination and CPPU treatment increased endogenous IAA content and decreased endogenous ABA content to promote the set and growth of fruit during early development. Chemical names used: [1-(2-chloro-4-pyridyl)-3-phenylurea] (CPPU); indole-3-acetic acid (IAA); abscisic acid (ABA).

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Gregory E. Welbaum

It is unclear from previous reports whether muskmelon seeds require an afterripenig period to attain maximum germinability and vigor. In the current study, seeds ranging in age from 30 to 60 days after anthesis were stored at water contents ranging from 3 to 15% and at either 6 or 30°C to determine whether seed vigor increased during storage. Changes in vigor were assessed by conducting monthly germination tests on blotter papers saturated with water or polyethylene glycol solutions of known water potential. The germination percentages of immature seeds (30 and 35 DAA) were dramatically improved by 3 months of storage at low water content and temperature, while the mean time to germination and the variability of germination were reduced for all stages of development. Germination percentages in water decline after storage at high water content and temperature with immature seeds showing a greater rate of decline than mature seeds but at reduced water potentials, the same adverse storage conditions increased the germination percents es and rates of mature seeds. However prolonged storage under adverse conditions, resulted in a gradual decline in water stress tolerance. Afterripening occurred over a wide range of storage conditions and significantly improved seed vigor, particularly in immature seeds. Furthermore, the increases in vigor achieved from afterripening treatments were remarkably similar to the increases in vigor attained through priming. Priming may substitute for the afterripening requirement of muskmelon seeds.

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W.D. Scott

Greenhouse and field studies were conducted using research coolers to expose 4 week old `Superstar' muskmelons, planted into 1 liter plastic containers, to chilling temperatures. Temperatures of 1, 5, & 9 °C were arranged in factorial combination with lengths of exposures 6, 12, & 24 hours and number of exposures 1, 3, & 5. In the Greenhouse studies single plant experimental units were allowed to grow for 2 weeks following application of the chilling treatments, then growth data was taken. In field studies, exposed muskmelons were planted into 8 plants/plot units when all plants had received chilling treatments. Leaf area and plant dry weight of `Superstar' melons were significantly reduced by both the interaction of temperature and length of exposure and times exposed and temperature, with dramatic reductions in leaf area occurring at 24 hours of exposure or 5 times exposed at 1 °C. A significant interaction was found between times exposed or length of exposure and temperature on vine length, flower number and type measurements taken 4 weeks after chilled transplants were established in the field. Additionally, fruit number and mean melon weight were reduced by ether exposure to 10C, exposure of 24 hours or 3 times exposed.

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Christopher Gunter* and Frankie Lam

Indiana ranks seventh in the nation for watermelon production and fifth in the nation in muskmelon production. Both of these crops are intensively managed and cultivation using plastic mulches is the industry standard in the area. The purpose of this study was to determine the effect of plastic mulches of various colors and breakdown properties on the yield and earliness of eastern muskmelons in southwestern Indiana in 2002 and 2003. In 2002, eight colors were used, black, clear, brown, green, olive, grey, blue, and red. In 2003, five colors were used, grey, black, blue, clear, and olive. A bare ground treatment was also included in 2003. Temperature information was also collected both above and below these plastics in attempt to relate that back to performance of the crop. In 2002, green and clear mulches produced more melon numbers and higher melon weights compared to other mulch colors, however this was not significantly different than the black control mulch. In 2003, olive mulch produced significantly higher melon number and weight than clear mulches. In 2003, early-breakdown clear mulches, designed to last only until canopy fill, produced significantly lower yields than early-breakdown black mulch. This appears to be due primarily to weed production initiated early under the clear mulch and subsequent weed growth after mulch was broken down. The effect of plastic mulch type and earliness to crop maturity is also explored.

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James R. Dunlap, Sarah E. Lingle, and Gene E. Lester

Postharvest ethylene production and ACC levels were determined in netted muskmelon fruits (Cucumis melo L. var. reticulatus `Magnum 45') exposed to temperature extremes by heating for 3 hr at 45C and/or storage at 4C. The possibility of using seal-packaging to protect the fruit against temperature-induced changes in ethylene production was examined by wrapping melons before treatment with a high-density polyethylene (HDPE) shrink-film. Ethylene production measured in fruit immediately after heating or removal from refrigeration was only 30% of the level determined before treatment, and continued to decline during refrigerated storage. However, the concentration of ACC in these same tissues remained constant or even increased slightly during storage. Wrapping fruit in HDPE film had no effect on the tissue concentrations of ACC or capacity for ethylene synthesis. In contrast to initial measurements, heated or refrigerated fruit held at room temperature (25C) for 24 hr produced ethylene at rates that equalled or exceeded the levels for freshly harvested fruit. These results strongly suggest that temperature-imposed restrictions on ethylene synthesis by netted muskmelon fruit are reversible and occur at the step responsible for converting ACC to ethylene via EFE rather than in the synthesis of ACC. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC).

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Natalie L. Hubbard, D. Mason Pharr, and Steven C. Huber

Muskmelon (Cucumis melo L.) fruit lack a stored starch reserve and therefore depend on translocated photoassimilate from the leaf canopy for sugar accumulation during ripening. The influence of canopy photosynthesis on sucrose' accumulation within muskmelon fruit mesocarp was examined. Canopy photosynthetic activities were estimated in a sweet and a nonsweet genotype. Photosynthetic rate of the nonsweet genotype, on a per-plant basis, was only 56% of that of the sweet genotype. The effect of limiting leaf area of the sweet genotype on carbohydrate concentrations and sucrose metabolizing enzymes within the fruit was evaluated. A 50% reduction of leaf area 8 days before initiation of fruit sucrose accumulation resulted in canopy photosynthesis similar to that of the nonsweet genotype. Reduced photosynthetic activity resulted in slightly lower soluble-carbohydrate concentration in the fruit; however, fruit sucrose concentration was three times higher than that reported previously for the nonsweet genotype. The extent to which `fruit sucrose phosphate synthase (SPS) activity increased during maturation was diminished by leaf removal. Acid invertase activity declined in all fruit in a similar manner irrespective of defoliation. A reduction of leaf area of a sweet genotype reduced sucrose accumulation within the fruit. Lower fruit sucrose concentration was associated with lower concentration of raffinose saccharides and lower SPS activity within the fruit. Additionally, insufficient assimilate supply was judged not to be the factor responsible for low sucrose accumulation in a nonsweet genotype.

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D.R. Waterer

The efficacy and cost efficiency of using various plastic soil mulches in the production of pepper (Capsicum annuum L.), corn (Zea mays L.) and muskmelon (Cucumis melo L.) were examined over four growing seasons in Saskatchewan, Canada. Clear mulch with or without preemergent herbicides was compared with black or wavelength selective mulches. In all three crops, mulches enhanced yields relative to bare ground in most site-year combinations. Clear mulch usually produced the highest yields. Herbicides applied under the clear plastic provided effective weed control with no observable changes in product efficacy or toxicity to the crop. The weed control provided by the herbicides had no effect on yields in the clear mulch treatments. Consequently, clear mulch without added herbicide usually represented the most cost-effective production option for all three crops.

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W.J. Lamont, D.L. Hensley, S. Wiest, and R.E. Gaussoin

Two systems of relay-intercropping muskmelons (Cucumis melo L.) with Scotch pine (Pinus sylvestris L.) Christmas trees using black plastic mulch and drip irrigation were evaluated for their potential to improve cash return. Returns ranged from a high of $26,200/ha for plastic mulch-drip irrigation and a selling price of $l.00/melon to a low of $6900/ha for bare ground-drip irrigation and a selling price of $0.40/melon. The benefit-cost index ranged from 24 to 3.4, depending on the system evaluated. Pine growth apparently was impeded by plastic mulch; however, increased yields of melons grown under plastic mulch may offset the slight decrease in pine growth.

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K.S. Mayberry and T.K. Hartz

Trials were conducted in California to evaluate techniques to extend storage life of netted muskmelons (Cucumis melo L.). The use of polyethylene bags, either as individual melon wraps or as liners for 18-kg commercial cartons, minimized water loss and associated deterioration of the fruit. Individual bags and carton liners were equally effective. A 3-minute dip in 60C water effectively checked surface mold development on wrapped fruits. Lower temperature and/or shorter exposure treatments were less effective. When applied in addition to hot water treatment, imazalil fungicide did not confer significant additional benefit. The combination of polyethylene bags and hot water treatment maintained high quality, marketable fruit for at least 28 days of storage at 3C,