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Abstract
In a stratified shipment of coconuts (Cocos nucifera L.), stress cracks occurred more frequently in the top of the load. Stress cracks and coconut weight loss were directly related. Of the total number of cracked coconuts, 81% occurred within the top section of the load, 10% in the middle, and 9% in the bottom section; while 43% of the total weight loss occurred within the top section, 27% in the middle, and 30% in the bottom section. The average percentages of cracked coconuts for each treatment over all 3 sections were 13.1% for the nonwaxed control, 5.2% for carnauba wax-treated, and 0.4% for paraffin wax-treated.
Abstract
Forty-two isolates of Fusarium oxysporum f. sp. niveum, causal agent of fusarium wilt of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai], from eight states and one foreign country were race-typed based on the disease reaction of three differential cultivars. F. oxysporum f. sp. niveum race 1 was identified from each of the eight states and accounted for 45% of the isolates. Race 2 was identified from only three states (Texas, Oklahoma, and Florida), but accounted for 33% of the isolates. Race 0 was also found in these same three states, but only accounted for 9% of the isolates. Race 2 was first described in the United States from Texas in 1981 and appears to be spreading within the southern states.
Abstract
‘Magnum 45’ muskmelon fruit, (Cucumis melo L. var. reticulatus Ser.) either shrink-film-wrapped to maintain a water-saturated microatmosphere or non wrapped, were stored in 4°C, 85-95% RH, and were sampled at 10-day intervals for 40 days postharvest. Fruits maintained in a water-saturated microatmosphere via shrinkwrap exhibited no significant change in percentage of dry weight, firmness, soluble sugars, β-carotene, or a loss of membrane integrity throughout 40 days storage. Shrink-wrap fruit had a 1% reduction in fresh weight, and a decline in appearance rating and surface browning by 40 days postharvest but were generally rated as excellent to good salable quality. Unwrapped fruit maintained in 85-95% RH exhibited progressive decline in appearance, surface browning, percentage of dry weight, soluble sugars, mesocarp firmness, and loss of membrane integrity. No change was observed in β-carotene. Non wrapped fruit had a 5.7% reduction in fresh weight within 20 days postharvest and were generally rated as fair to poor salable quality. Mesocarp membrane integrity during postharvest storage was highly dependent on percentage of fresh weight loss over time for both shrink-film-wrapped and non wrapped muskmelon fruit.
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.
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.
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.
Abstract
Infection by Macrophomina phaseolina (Tassie) Goid and subsequent symptom expression were investigated on ‘Perlita’ and ‘TAM Uvalde’ muskmelon (Cucumis melo L.) at 3 spring planting dates. Infection exceeded 80% within 49 days of planting in both cultivars at all planting dates. Symptom expression at harvest was significantly greater in ‘Perlita’ than ‘TAM Uvalde’ for all planting dates, indicating a useful level of tolerance in ‘TAM Uvalde’.
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.
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.