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S. Alan Walters and Jonathan R. Schultheis

Seedling losses shortly after emergence in muskmelon (Cucumis melo L.) can be potentially devastating to growers. Muskmelon growers often have problems with obtaining adequate stands and need to understand the affects of replanting seed into poor stands. Field studies were conducted over 2 years to determine if replanting (at 1, 2, 3, or 4 weeks after the initial seeding) into stand deficiencies of 10%, 30%, and 50% affected `Athena' muskmelon size and yield. `Athena' muskmelon stand deficiencies up to 30% does not appear to reduce total or marketable numbers, but stand deficiencies of 50% or more will decrease total and marketable melon yields. Replanting into 10%, 30%, and 50% stand deficiencies will increase early season melon numbers regardless of the replant times used. For main-season and total-season harvests, there was no advantage of replanting into 10% deficient stands, and in most cases, replanting reduced total and marketable melon numbers. In the 1997 experiment, replanting into 30% and 50% stand deficiencies improved yields but this did not occur in the 1998 experiment. `Athena' muskmelon should be replanted only if a stand reduction of ≈50% or more occurs. Melon numbers were generally higher if replanted by 1 or 2 weeks compared to 3 or 4 weeks, but the timing of replanting does not appear to have significant influence on total or marketable melon numbers.

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Warley M. Nascimento and Sherlie H. West

The effects of seed priming and seed orientation on seedcoat adherence and seedling development of containerized muskmelon transplants were investigated. Seeds of muskmelon `Top Net SR' were primed for 6 days in darkness at 25 °C in an aerated solution of KNO3 (0.35 M). Primed and nonprimed seeds were individually planted in Styrofoam trays in the greenhouse. Seeds were carefully oriented with the radicle down, up, or in the horizontal position, and covered with 0.5 cm of the growing mix. Seed priming and seed orientation affected both seedcoat adherence and seedling development, and interaction between priming and orientation was significant for seedcoat adherence. Our data indicate that seed priming can minimize seedcoat adherence during emergence of muskmelon seeds.

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Warley M. Nascimento and Sherlie H. West

The effects of seed priming and seed orientation on seedcoat adherence and seedling development of containerized muskmelon transplants were investigated. Seeds of muskmelon `Top Net SR' were primed for 6 days in darkness at 25 °C in an aerated solution of KNO3 (0.35 m). Primed and nonprimed seeds were individually planted in Styrofoam trays in the greenhouse. Seeds were carefully oriented with the radicle down, up, or in the horizontal position, and covered with 0.5 cm of the growing mix. Seed priming and seed orientation affected both seedcoat adherence and seedling development, and interaction between priming and orientation was significant for seedcoat adherence. Our data indicate that seed priming can minimize seedcoat adherence during emergence of muskmelon seeds.

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Paul R. Adler and Gerald E. Wilcox

Two mechanisms that reduce water and salt stress, respectively, are an increase in root hydraulic conductivity (LP) and reduction in Na and Cl absorption and transport to the leaf. NH4 +-N decreased muskmelon LP 55-70% while under 100 mM NaCl stress and 40-50% in the absence of NaCl stress. A decrease in LP increases the rate of water stress development as the transpiration rate increases. Although dry weight decreased about 70%, with NO- 3-N, muskmelon remained healthy green, while with NH+ 4-N they became chlorotic and necrotic with a 100% and 25% increase in leaf blade Na and Cl compared to NO- 3-N, respectively. Further investigation indicated that NH+ 4-N increased muskmelon sensitivity to NaCl through both an increased rate of net Na influx and transport of Na to the leaf. Since Na influx partitioning is controlled by mechanisms K/Na selectivity and exchange across membranes, the NH+ 4-N inhibition of K absorption may impair K/Na exchange mechanisms. Reduced K/Na selectivity or Na efflux are implicated as the source of the increased net Na influx with NH+ 4-N. The importance of K in preventing Na partitioning to the leaf was confined through removal of K from the nutrient solution thereby simulating the NH+ 4-N-induced gradual K depletion in muskmelon. Our work indicates that at a given level of water or NaCl stress, NO- 3-N reduces the level of stress experienced by muskmelon through increasing LP and reducing the net rate of Na influx and transport to the sensitive leaf blade. This avoidance mechanism should enable muskmelon plants fertilized with NO- 3-N to tolerate greater levels of stress.

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Paul R. Adler and Gerald E. Wilcox

Two mechanisms that reduce water and salt stress, respectively, are an increase in root hydraulic conductivity (LP) and reduction in Na and Cl absorption and transport to the leaf. NH4 +-N decreased muskmelon LP 55-70% while under 100 mM NaCl stress and 40-50% in the absence of NaCl stress. A decrease in LP increases the rate of water stress development as the transpiration rate increases. Although dry weight decreased about 70%, with NO- 3-N, muskmelon remained healthy green, while with NH+ 4-N they became chlorotic and necrotic with a 100% and 25% increase in leaf blade Na and Cl compared to NO- 3-N, respectively. Further investigation indicated that NH+ 4-N increased muskmelon sensitivity to NaCl through both an increased rate of net Na influx and transport of Na to the leaf. Since Na influx partitioning is controlled by mechanisms K/Na selectivity and exchange across membranes, the NH+ 4-N inhibition of K absorption may impair K/Na exchange mechanisms. Reduced K/Na selectivity or Na efflux are implicated as the source of the increased net Na influx with NH+ 4-N. The importance of K in preventing Na partitioning to the leaf was confined through removal of K from the nutrient solution thereby simulating the NH+ 4-N-induced gradual K depletion in muskmelon. Our work indicates that at a given level of water or NaCl stress, NO- 3-N reduces the level of stress experienced by muskmelon through increasing LP and reducing the net rate of Na influx and transport to the sensitive leaf blade. This avoidance mechanism should enable muskmelon plants fertilized with NO- 3-N to tolerate greater levels of stress.

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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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M.S. Stanghellini, J.R. Schultheis, and J.T. Ambrose

Very little is known about the rate at which pollen grains are mobilized within insect-pollinated crop systems, and this is especially true the for commercial production of field-grown cucumber (Cucumis sativus L.), monoecious muskmelon (Cucumis melo L.), and triploid watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai]. The rates of pollen depletion for these crops were therefore investigated on plots simulating commercial crop production using a mixed honey bee (Apis mellifera L.) and bumble bee (Bombus impatiens Cresson) pollinator complex. At anthesis, staminate cucumber, muskmelon, and watermelon flowers contained on average 10539, 11176, and 30739 pollen grains/flower, respectively. At the time flowers closed in the early afternoon (1300 to 1400 hr), only 61% of the total pollen produced had been removed from staminate cucumber flowers, 44% to 62% from muskmelon, and 81% from watermelon flowers. The results suggest that total pollen production in these crops may not necessarily reflect total pollen availability to floral visitors (bees). However, of the total amount of pollen actually removed per flower, >57% occurred during the 2 h following flower anthesis of cucumber and muskmelon, and >77% occurred during the 2 h following flower anthesis of watermelon. Thus, most of the accessible pollen was removed shortly after anthesis, which is when these crops are most receptive to pollination. Nonviable triploid and viable diploid watermelon pollen were removed at similar rates (P = 0.4604). While correlation analyses were not possible for the influence of variable bee abundance on pollen depletion rates, higher bee populations in one year appeared to increase the rate at which pollen grains were removed from staminate flowers.

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Gene E. Lester

Plasma membrane (PM) from hypodermal-mesocarp tissues of muskmelon fruits (Cucumis melo L. var. reticulatus Naud.) were compared to the electrolyte leakage changes of the same tissue during maturation and storage at 4 or 24C. During fruit maturity and storage, leakage of the hypodermal-mesocarp tissue increased, which is coincident with increased total sterol: total phospholipid ratios and increased phospholipid fatty acid saturation index of the PM. ATPase activity, a marker for the PM, indicated that the PM increased in buoyant density from 1.13 g.cm-3 to 1.14 g.cm-3 during maturity and ATPase activity peaked with fruit maturation. ATPase activity decreased with 10 days postharvest storage and was less at 24C vs. 4C, which was coincident with increased hypodermal-mesocarp electrolyte leakage. Biochemical changes within the sterol and phospholipid matrix of the PM are suggested to contain the processes capable of altering fruit membrane permeability and subsequent muskmelon fruit storage life.

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J.C. Rodriguez, D.J. Cantliffe, N.L. Shaw, and Z. Karchi

In the spring of 2001 and 2002, different combinations of media (coarse perlite, medium perlite, and pine bark) and containers (polyethylene bags and plastic pots) were used for hydroponic production of `Galia' muskmelons (Cucumis melo L.) to determine their effect on fruit yield and quality, and their influence on costs of production. Marketable yields obtained for `Gal-152' in the spring 2001 and 2002 were 25.5 kg·m–2 and 39.0 kg·m–2 respectively. When data were combined for 2001 and 2002, fruit yield and fruit quality were unaffected by any combination of media and container. Average soluble solids content was generally greater than 10° Brix. It was determined that the use of pine bark media and plastic pots instead of perlite and bags would save $18,200 per year (two crops)—a feasible option for reducing costs of producing `Galia' muskmelons in greenhouses using soilless culture without loss of yield and fruit quality.