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Sannai Gong and Kenneth A. Corey

It frequently takes days or weeks to determine if desired steady state concentrations of gases are reached in modified atmosphere packages of produce when atmospheres are modified by commodity respiration. We present a rapid method for testing packaging films and designs with active modification of atmospheres by vacuum and N2 infusion. Reduction of O2 concentration in produce packages and commodity tissues was completed within minutes by using several cycles of vacuum and N2 infusion treatments. Produce packages were placed in a desiccator and subjected to repeated partial vacuums, each followed by infusion of N2 to one atmosphere. Resulting O2 concentrations in packages (polyethylene + ethyl-vinyl acetate additive) were dependent on the extent of vacuum and the number of evacuations. Within packages of tomatoes, O2 concentrations of 8.3% ± 0.5% and 5.0% ± 1.0% were measured following two evacuations at 460 and 360 mm Hg, respectively. Three evacuations of cabbage and muskmelon packages at 460 mm Hg resulted in O2 concentrations of 5.1% ± 1.4% and 5.0% ± 1.4%, respectively. Maintenance or deviation from actively established atmospheres by the film was determined within hours.

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Kevin Crosby, David Wolff, and Marvin Miller

The fungus Monosporascus cannonballus Pollock and Uecker infects melon (Cucumis melo L.) roots and causes root rot/vine decline disease, which has reduced productivity of commercial muskmelon and honeydew cultivars in South Texas. To assess the impact of the fungus on several root traits, two greenhouse experiments were carried out over two seasons. A comparison of inoculated vs. control root systems was carried out with four melon cultivars representing both susceptible (`Magnum 45' and `Caravelle') and tolerant types (`Deltex' and `Doublon'). The sand medium was inoculated with 50–60 colony forming units (CFUs) per gram of the severe Monosporascus strain, TX90-25. After a 30-day growth period, the control and inoculated root systems were carefully cleaned and evaluated. Roots were scanned by a computer and the data were analyzed by the Rhizo Pro 3.8 program. The traits of interest included total root length, average root diameter, number of root tips, number of fine roots (0–0.5 mm), and number of small roots (0.5–1 mm). Significant differences existed between the two tolerant cultivars and the two susceptible ones for four of the traits. Total root length, fine and small root length, and root tip number were greater for `Deltex' than for both susceptible cultivars and greater for `Doublon' than for `Caravelle'. The results suggest that tolerance to this pathogen is closely linked to the integrity of the root structure. The potential for improving root vigor to combat root rot/vine decline merits further investigation.

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Javier Farias-Larios, Mario Orozco-Santos, and Salvador Guzman-Gonzalez

Muskmelon (Cucumis melo L.) is the major cucurbit crop in the Colima state, Mexico. The use transparent plastic mulch continues to increase in that region for high production technology systems of muskmelon, and more recently floating rowcovers were introduced to protect cucurbits from insects (direct pests or vector of viruses) and to increase yield of cucurbit crops. During 1993, yield was evaluated of three cultivars of muskmelon (`Crushier', `Laguna', and `Durango') growing on transparent polyethylene mulch alone or with floating rowcover. The cultivar Crushier showed the higher yield 40 ton/ha (77% for export market), followed by `Durango' with 28.5 ton (77% for export quality) and `Laguna' with about 23 ton (only 40% of export fruit). There was no significant difference in yield between cultivar growth on transparent mulch plots alone and combined with floating rowcover. Also, floating rowcover excluded (until perfect flowering) beetles leafminers, sweetpotato whitefly, and aphids, reducing the use of insecticide by 50%.

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Dongsheng Zhang, James R. Brandle, Kenneth G. Hubbard, Laurie Hodges, and Entin Daningsih

The relationships between shelterbelt (tree windbreak)-induced microclimate and muskmelon (Cucumis melo L.) growth and development were investigated at the Univ. of Nebraska-Lincoln Agricultural Research and Development Center near Mead, Nebr., during the 1992 and 1993 growing seasons. Wind speed, wind direction, air and soil temperatures, relative humidity, and soil moisture were monitored in both sheltered and nonsheltered areas. Plant growth parameters (plant height, vine length, plant dry weight, and leaf area) were measured at various stages of development. Shelterbelts provided improved growing conditions for muskmelon transplants. Direct wind damage and duration of higher wind speeds were reduced 47% to 56% in sheltered areas. Air temperatures in sheltered areas were slightly higher during daytime and slightly lower at night, and significantly so early in the growing season. Relative humidity was increased significantly in sheltered areas in 1992 and, while higher in 1993, the difference was nonsignificant. Soil moisture content was not affected significantly by wind protection. Sheltered plants exhibited earlier development and faster growth. The first female flower appeared 2 days earlier in sheltered areas in both years. The first fruit set, as indicated by fruit swelling and retention on the vine, occurred 6 days earlier and matured 5 and 6 days earlier in sheltered areas in 1992 and 1993, respectively. Leaf areas and dry-matter accumulation of sheltered plants were greater than those of exposed plants. The shoot relative growth rate of sheltered plants increased earlier in the growing season, but decreased slightly later in the growing season. The earlier development and faster growth of sheltered plants were related mainly to the reduction of wind speed, higher total accumulated air temperatures during the daylight hours (sum of daily average daytime air temperatures based on hourly averages), and higher soil temperature in sheltered areas. Total yields were not affected significantly in either year; however, early yields were significantly greater in sheltered areas in 1993. If earlier maturity and increased yield are possible in large sheltered fields, this practice would provide an economic benefit to producers.

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David W. Wolff, Marvin E. Miller, and Carmen Lander

The nature and magnitude of genotype × environment interactions will determine the extent of testing required (locations, years) to accurately evaluate a genotype's performance. Data from yearly T-AES muskmelon variety trials were analyzed to determine the level of variety (V) × year (Y), V × location (L), and V × Y × L interactions for yield and fruit size. Data analyzed were of nine hybrids grown at three commercial farms over two years. Fruits were harvested similar to grower practices, and were sorted into size classes (9 - 30) or culls. V × Y and V × L interactions for marketable yield and total yield were not significant. V × Y × L interaction was significant for marketable yield, but not for total yield. V × Y × L interactions were highly significant for percentage culls and percentage of fruit in each size class. V × L interactions were also significant for percentage of fruit in most size classes. Data indicate that specific location-year combinations differentially affect a genotype's fruit size, most likely due to weather, planting time, and stress factors. Multiple year and location testing of genotypes is therefore critical, particularly for evaluation of fruit size.

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W.D. Scott and E.T. Maynard

Muskmelons (Cucumis melo L. cv. Superstar) were grown at two between-row spacings (1.5 m or 2.1 m) and four in-row spacings (0.6, 0.9, 1.2, or 1.5 m), corresponding to populations from 3074 to 10763 plants ha-1, to determine the influence of row spacing and population on melon growth and yield. The study was conducted at two sites in 1993, one in northern and one in southern Indiana. Numbers of flowers and early season vine growth were not significantly different between treatments. In southern Indiana, the number of fruit harvested per plot increased as in-row spacing decreased; means ranged from 5.2 fruit plot-1 for 0.6 m in-row spacing, to 4.7 fruit for 0.9 m in-row spacing, 3.9 fruit for 1.2 m in-row spacing, and 3.3 fruit for 1.5 m in-row spacing. Harvests were significantly earlier for the 0.6 m in-row spacing. Mean melon weight was significantly greater for 1.5 m in-row spacing, averaging 4.1 kg, compared to 3.8, 3.7, and 3.7 kg for 0.6, 0.9, and 1.2 m in-row spacings, respectively. Between-row spacing did not affect number or weight of melons. There were no significant interactions between in-row and between-row spacings.

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J.R. Dunlap, S.J. Maas, J.F. Gomez, and R. LaGrange

Two muskmelon (Cucumis melo L.) cultivars, Mission and Laguna, were direct-seeded in spring plantings separated by 30 days at the TAES farm in Weslaco. Females were tagged each morning for 8 consecutive days beginning on the first day of flowering and evaluated for fruit set 15 to 20 days later. Mean numbers of flowers and fruits produced on individual plants were compared across cultivars and planting dates. The flowering patterns appear to be bimodal with the majority of blooms occurring during the first 5 days followed by a sharp decline on day 6 and gradual increase, thereafter. The majority of the fruit is set during the first 5 days of flowering and failed to increase with the subsequent rise in flowering. Mission produced approximately 30% more female flowers per plant than Laguna; however, fruit numbers were the same for both cultivars. The environmental conditions associated with earlier plantings suppressed flowering in Laguna but had no effect on the daily rate of fruit-set. Fertilization and fruit set appear to be relatively unaffected by the population dynamics of female flowering.

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Gregory E. Welbaum

Muskmelon (Cucumis melo L.) seed crops sometimes contain seeds with split coats that expand to twice their normal water content. These expanded seeds are often referred to as “fishmouth” seeds, because the split seed coat resembles an open fish's mouth when viewed longitudinally. “Fishmouth” seeds are dead seeds. However, little is known about why death occurs inside the fruit before harvest. Hermaphroditic flowers were tagged at anthesis and fruits were harvested at various intervals during the later stages of development and decay. Seeds were removed from the fruits and incubated in water on germination blotter paper for 14 days. The percentage of germinable, dead and “fishmouth” seeds were averaged for each Harvest date. Fruit pericarp samples were analyzed for pH, ethanol, and acetic acid content. At 50 days after anthesis (DAA), just past edible maturity, 100% of the seeds germinated. However, at 60 and 78 DAA germination dropped to 60 and 17%, respectively, while the occurrence of “fishmouth” seeds increased from 2 to 54% over the same period. The ethanol content of the tissue increased from 0.11 to 0.28%, the pH dropped from 6.2 to 5.1, and acetic acid concentration increased from 3.0 to 3.7 mM from 50 to 60 DAA, respectively. However, when dried seeds were incubated in the laboratory under conditions similar to those within the fruit, the formation of “fishmouth” seeds was related to the ageing effects of long term hydration and was not correlated with any chemical product within the fruit.

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Elizabeth T. Maynard, Charles S. Vavrina, and W. Dennis Scott

Muskmelon (Cucumis melo L. cvs. Superstar and Mission) transplants were grown in cellular seedling trays of polystyrene or styrofoam, with individual cells ranging in volume from 7 to 100 cm3, transplanted to the field, and grown to maturity in Florida and Indiana during the 1993 and 1994 growing seasons. Seedling leaf area, shoot and root weights before transplanting, and shoot dry weight 20 days after transplanting increased linearly with increasing cell volume in Florida. Thirty days after transplanting, vine length showed significant linear and quadratic trends with respect to cell volume in Indiana. In Florida, early and total yields increased linearly as transplant cell volume increased for `Mission' in both years and for `Superstar' in 1994. In Indiana, early yields increased linearly as transplant cell volume increased for `Mission' in 1994 and for `Superstar' in both years, but cell volume did not consistently affect total yield. Transplant tray effects on early and total yield unrelated to linear or quadratic effects of cell volume occurred in both locations, but these effects were not consistent.

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J.C. Palumbo and C.A. Sanchez

Imidacloprid is a new, chloronicotinyl insecticide currently being used to control sweetpotato whitefly [Bemisia tabaci Genn, also known as silverleaf whitefly (Bemisia argentifolii Bellows and Perring)]. Large growth and yield increases of muskmelon (Cucumis melo L.) following the use of imidacloprid have caused some to speculate that this compound may enhance growth and yield above that expected from insect control alone. Greenhouse and field studies were conducted to evaluate the growth and yield response of melons to imidacloprid in the presence and absence of whitefly pressure. In greenhouse cage studies, sweetpotato whiteflies developed very high densities of nymphs and eclosed pupal cases on plants not treated with imidacloprid, and significant increases in vegetative plant growth were inversely proportional to whitefly densities. Positive plant growth responses were absent when plants were treated with imidacloprid and insects were excluded. Results from a field study showed similar whitefly control and yield responses to imidacloprid and bifenthrin + endosulfan applications. Hence, we conclude that growth and yield response to imidacloprid is associated with control of whiteflies and the subsequent prevention of damage, rather than a compensatory physiological promotion of plant growth processes. Chemical names used: 1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-N-nitro-1-H-imidazol-2-amine (imidacloprid); [2 methyl(1,1′-biphenyl)-3yl)methyl 3-2-chloro-3,3,3-trifluoro-1-propenyl]-2,2-dimethylcyclopropane carboxylate (bifenthrin); 6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodiaxathiepin 3-oxide (endosulfan).