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John D. Abbott, B.D. Bruton and C.L. Patterson

Four fungicides were evaluated for their effects on in vitro pollen germination of muskmelon (Cucumis melo L.) cultivars TAM-Uvalde and Magnum 45. Cupric hydroxide, mancozeb, and chlorothalonil reduced the percentage of pollen that germinated and rate and length of germ-tube elongation, regardless of cultivar. Benomyl had very little overall effect on pollen germination or germ-tube elongation. With the effective pollination period of ≈ 10 to 14 days in commercial production, each day is critical for maximum crown set. Based on our results. some fungicides may be contributing to reduced fruit set in muskmelon.

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J.X. Zhang, B.D. Bruton and C.L. Biles

Phomopsis cucurbitae is a latent infecting pathogen that infects unripe muskmelon fruit, but causes decay after harvest. This fungus causes severe losses during muskmelon fruit storage and marketing in the U.S., Japan, and some Central American countries. Previous studies showed that the fungus produced the cell wall-degrading enzyme polygalacturonase (PG) in both culture and muskmelon fruit tissue. The role of P. cucurbitae PG in the fruit decay process and its relation to latent infection is not well-understood. A prominent PG isozyme produced by the fungus in decayed fruit was purified to homogeneity by a sequence of extraction, ultrafiltration, preparative isoelectric focusing, anion exchange, and gel filtration chromatography. This isozyme exhibited endo-activity, a molecular weight of 54 kDa according to SDS-PAGE, and a pI of 4.2 based on IEF-PAGE. Isozyme activity was optimal at 40–45°C and pH 5.0. It had a Km of 44.7 g/ml and a Vmax of 0.313. The purified isozyme also effectively macerated mature muskmelon fruit tissues. This isozyme was the most prominent of the PG isozymes produced by P. cucurbitae in decaying fruit, and may play an important role in postharvest decay.

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J.K. Collins, B.D. Bruton and P. Perkins-Veazie

Organoleptic evaluations of shrink film-wrapped and nonwrapped musk-melon (Cucumis melo L. var. reticulates cv.. TAM Uvalde) fruit were conducted to determine changes in flavor and taste during refrigerated storage. Ripe green and yellow `TAM Uvalde' muskmelons, shrink film-wrapped in 12.7-μm high-density polyethylene film, were compared to nonwrapped melons during 21 days of storage at 4C and 90% to 95% RH. After 21 days of storage, both yellow and green shrink-wrapped melons had better appearance, less surface mold, and less vein tract browning than nonwrapped melons. However, the flavor and taste of shrink-wrapped fruit were significantly inferior to those of nonwrapped melons. Green-wrapped melons were rated poorer in taste and flavor than yellow-wrapped and nonwrapped melons after 14 days of storage. These results indicate that shrink-wrapping may enhance undesirable flavor changes in muskmelon during storage.

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Ray D. Martyn, J. C. Mertely, M. E. Miller and B. D. Bruton

A disease of muskmelon (Cucumis melo L.) characterized by a vine decline and a cortical root rot was first observed in the Lower Rio Grande Valley of Texas in 1986. In 1990, isolations from diseased plants collected from four commercial production fields yielded the fungus Monosporascus cannonballus. Pathogenicity tests with eight isolates confirmed Koch's postulates; however, there were differences in aggressiveness observed among isolates. M. cannonballus is an ascomycete fungus that typically produces only one (rarely two), round, jet-black ascospore per ascus. There is no known asexual stage. Temperature optimum of one isolate was 35 C. The optimum pH for growth was 6-7, but it grew well up to pH 9. M. cannonballus was first reported on muskmelon in 1970 from Arizona and recently was found in Japan under glass house culture. The presence of this fungus in Texas marks only the third report of this species worldwide, although a similar species (M. eutypoides) is the cause of a collapse of melon plants in Israel.

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B.D. Bruton, T.W. Popham, J. García-Jiménez, J. Armengol and M.E. Miller

Thirty-seven species within Cucurbitaceae representing the genera Citrullus, Cucumis, Cucurbita, Lagenaria, and Luffa were evaluated for disease reaction to an Acremonium cucurbitacearum A. Alfaro-Garcia, W. Gams, and Garcia-Jimenez, isolate (TX 941022) from the Lower Rio Grande Valley of Texas. After 28 days in the greenhouse, seedling disease ratings were made on the hypocotyl, stem-root junction, primary root, and secondary roots. An additional disease measure was derived by averaging the four root disease ratings to establish a disease severity index (DSI). Vine and root dry weight were poor measures of plant damage caused by A. cucurbitacearum. According to the DSI, all species within Cucurbita, Lagenaria, Luffa, and three Cucumis sativus L. cultigens were rated as highly resistant to A. cucurbitacearum. Cucumis melo L. and Citrullus lanatus (Thunb.) Matsum. & Nakai cultigens were the only cucurbits receiving DSI ratings of moderately resistant to susceptible.