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Gene E. Lester, John L. Jifon and D. J. Makus

Netted muskmelon [Cucumis melo L. (Reticulatus Group)] fruit quality (ascorbic acid, β-carotene, total free sugars, and soluble solids concentration (SSC)) is directly related to plant potassium (K) concentration during fruit growth and maturation. During reproductive development, soil K fertilization alone is often inadequate due to poor root uptake and competitive uptake inhibition from calcium and magnesium. Foliar applications of glycine-complexed K during muskmelon fruit development has been shown to improve fruit quality, however, the influence of organic-complexed K vs. an inorganic salt form has not been determined. This glasshouse study investigated the effects of two K sources: a glycine-complexed K (potassium metalosate, KM) and potassium chloride (KCl) (both containing 800 mg K/L) with or without a non-ionic surfactant (Silwet L-77) on melon quality. Orange-flesh muskmelon `Cruiser' was grown in a glasshouse and fertilized throughout the study with soil-applied N–P–K fertilizer. Starting at 3 to 5 d after fruit set, and up to 3 to 5 d before fruit maturity at full slip, entire plants were sprayed weekly, including the fruit, with KM or KCl with or without a surfactant. Fruit from plants receiving supplemental foliar K had significantly higher K concentrations in the edible middle mesocarp fruit tissue compared to control untreated fruit. Fruit from treated plants were also firmer, both externally and internally, than those from non-treated control plants. Increased fruit tissue firmness was accompanied by higher tissue pressure potentials of K treated plants vs. control. In general, K treated fruit had significantly higher SSC, total sugars, total ascorbic acid, and β-carotene than control fruit. Fall-grown fruit generally had higher SSC, total sugars, total ascorbic acid and β-carotene concentrations than spring-grown fruit regardless of K treatment. The effects of surfactant were not consistent but in general, addition of a surfactant tended to affect higher SSC and β-carotene concentrations.

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Robert L. Long, Kerry B. Walsh, David J. Midmore and Gordon Rogers

A common practice for the irrigation management of muskmelon (Cucumis melo L. reticulatus group) is to restrict water supply to the plants from late fruit development and through the harvest period. However, this late fruit development period is critical for sugar accumulation and water stress at this stage is likely to limit the final fruit soluble solids concentration (SSC). Two field irrigation experiments were conducted to test the idea that maintaining muskmelon plants free of water stress through to the end of harvest will maximise sugar accumulation in the fruit. In both trials, water stress before or during harvest detrimentally affected fruit SSC and fresh weight (e.g., no stress fruit 11.2% SSC, weight 1180 g; stress fruit 8.8% SSC, weight 990 g). Maintaining plants free of water stress from flowering through to the end of harvest is recommended to maximise yield and fruit quality.

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Gary W. Elmstrom and Donald N. Maynard

Muskmelon (Cucumis melo L. reticulatus group), commonly called cantaloupe by growers, shippers, and consumers is a relatively minor crop in the southeastern U.S. The principal restraint on increased muskmelon production in this area is the lack of varieties that consistently produce high quality fruit. Resistance to both fruit rots, especially those induced by Fusarium, and foliar diseases such as downy mildew, powdery mildew, and gummy stem blight are also important because of the high humidity and frequent rainfall common to this area. The ideal shipping variety should have the capacity to produce high yields of round to oval, sutureless, heavily netted fruit that average 1.4 kg each, and that have a deep salmon-colored flesh, a small tight seed cavity, high soluble solids, and a pleasant taste and aroma. Evaluations at Leesburg and Bradenton, Florida over a three-year period have identified several western-type muskmelons well-adapted to this area. `Explorer', `Goldmark', `Mission', and `Tasty Sweet' ranked high in most of the categories mentioned above and should be evaluated in more extensive trials, which should include a study of postharvest quality.

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Gene E. Lester and Michael A. Grusak

Muskmelon senescence is directly associated with a decline in hypodermal mesocarp membrane integrity and its Ca concentration, but infusing Ca into melons has been a problem. Fully ripened and abscised hybrid honeydew [Cucumis melo L. (Inodorus Group) `Honey Brew'] and netted muskmelon [Cucumis melo L. (Reticulatus Group) `Explorer'] fruit were submerged (dipped) 20 min at 25 ± 3 °C in a solution containing a Ca-chelate, a Mg-chelate, a combination of both chelates, or no mineral chelate. Following 10 or 24 days of cold storage (4 °C for `Explorer' and 10 C for `Honey Brew'), fruit were analyzed for mineral content and various senescence-related parameters. Abscised `Honey Brew' fruit dipped in either Ca-chelate or (Ca+Mg)-chelate and abscised `Explorer' fruit dipped in (Ca+Mg)-chelate, followed by 10 days cold storage, had hypodermal mesocarp Ca concentrations of at least 6.0 mg·g-1 dry weight. Maintaining hypodermal mesocarp tissue Ca concentrations at this level during postharvest storage, especially for fully ripe `Honey Brew' fruit, maintained membrane integrity and fruit firmness, and extended storage life 2.4-fold (i.e., to 24 days). The senescence regulatory effect of postharvest Ca-chelate treatments on abscised `Explorer' was highly variable, compared to `Honey Brew', which appeared to be due to the surface netting interfering with movement of Ca into the hypodermal mesocarp. Thus, postharvest Ca-chelate application to abscised `Honey Brew' fruit could delay fruit senescence in commercial storage, and open up new markets for fully ripened honeydew melons.

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Clydette M. Alsup, Brian A. Kahn and Mark E. Payton

Hairy vetch (Vicia villosa Roth) cover crops were grown in a rotation with sweet corn (Zea mays var. rugosa Bonaf.) and muskmelon (Cucumis melo L. Reticulatus group) to evaluate the legume's ability to remove excess P from soils when poultry litter was used as a fertilizer. Fertilizer treatments were: 1) litter to meet each crop's recommended preplant N requirements (1×); 2) litter at twice the recommended rate (2×); and 3) urea at the 1× rate as the control. Following the vegetable crops, hairy vetch was planted on half of each replication, while the other half was fallowed. The vetch was removed from the field in a simulated haying operation in the spring. Soil samples were taken at 0-15 cm and 15-30 cm depths at the onset of the study and after each crop to monitor plant nutrient concentrations. The vetch sometimes raised soil test N concentrations at the 0-15 cm depth. Soil test P concentrations at the 0-15 cm sampling depth in the vetch system were consistently lower numerically, but not statistically, relative to comparable plots in the fallow system. Soil test P at the 0-15 cm depth was usually increased by litter at the 2× rate relative to the urea control, regardless of cropping system. Yields of both vegetable crops were similar among all cover crop and fertilizer treatments.

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Fahrurrozi Aziz, Katrine A. Stewart and Sylvie Jenni

Temperature modification is the most investigated environmental factor considered to affect muskmelon (Cucumis melo L. Reticulatus Group) growth in a mulched minitunnel production system. Until now, effects on CO2 concentrations within the tunnel have been ignored. Experiments on production of `Earligold' netted muskmelon were conducted in 1997, 1998, and 1999 to determine daily CO2 concentrations for 10 mulched minitunnel and thermal water tube combinations. Carbon dioxide concentrations under nonperforated (clear or infrared-blocking polyethylene) tunnels were significantly higher (three to four times) than that of ambient air. Soil respiration under the plastic mulch was primarily responsible for increased CO2 levels in the tunnel. Daily CO2 concentrations in the tunnels varied little during early muskmelon growth, but fluctuated widely as the plants developed. Ventilation significantly decreased CO2 concentrations in the tunnels but levels remained significantly above the control and perforated tunnel treatments. When using mulched minitunnels for muskmelon production, daily CO2 concentrations should be recognized as a significant factor influencing growth.

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Fahrurrozi Aziz, Katrine A. Stewart and Sylvie Jenni

Field experiments were conducted during 1997, 1998, and 1999 to determine effects of 10 combinations of mulched minitunnel and thermal water tube on air, soil, and water-tube temperatures and on vegetative growth of `Earligold' netted muskmelon (Cucumis melo L. Reticulatus Group) within the tunnels. Use of mulched minitunnels significantly increased air, soil and water temperatures during the preanthesis phase in all years compared with control treatments. Inclusion of water tubes and venting the tunnels decreased air temperature fluctuations in the tunnels. During the first 10 to 15 days after transplanting, plants grown in nonperforated tunnels had higher relative growth rates (RGRs), net assimilation rates (NARs), and dry weights (DWs) than those grown under perforated tunnels and control plots. Plants in tunnels containing thermal water tubes generally had higher RGRs, NARs, and DWs than those without tubes. During the later part of the experiment, from 11 to 16 days after transplanting until anthesis, however, there were no consistent effects of mulched minitunnels on RGR, NAR, and plant DW. Tunneled muskmelons had significantly higher RGRs, but generally lower NARs than those grown without tunnel. Use of mulched minitunnels significantly increased plant DW at anthesis in 1997, but not in 1998 and 1999. Plants grown in the minitunnels containing a thermal water tube generally had higher RGRs, NARs, and DWs than those without water tubes. Ventilating nonperforated tunnels generally increased RGR, NAR, and plant DW. Plants grown in the tunnels reached anthesis 10 days earlier than those without tunnels.

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José A. Franco and Daniel I. Leskovar

Containerized `Lavi' muskmelon [Cucumis melo L. (Reticulatus Group)] transplants were grown in a nursery with two irrigation systems: overhead irrigation (OI) and flotation irrigation (FI). Initially, root development was monitored during a 36-day nursery period. Thereafter, seedling root growth was monitored either in transparent containers inside a growth chamber, or through minirhizotrons placed in the field. During the nursery period, OI promoted increased early basal root growth, whereas FI promoted greater basal root elongation between 25 and 36 days after seeding (DAS). At 36 DAS leaf area, shoot fresh weight (FW) and dry weight (DW), and shoot to root ratio were greater for OI than for FI transplants, while root length and FWs and DWs were nearly the same. Total root elongation in the growth chamber was greater for FI than for OI transplants between 4 and 14 days after transplanting. Similarly, the minirhizotron measurements in the field showed a greater root length density in the uppermost layer of the soil profile for FI than for OI transplants. Overall, muskmelon transplants had greater root development initially when subjected to overhead compared to flotation irrigation in the nursery. However, during late development FI transplants appeared to have a greater capacity to regenerate roots, thus providing an adaptive mechanism to enhance postplanting root development and to withstand transplant shock in field conditions. At harvest, root length density and yield were closely similar for the plants in the two transplant irrigation treatments.

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D. Mark Hodges and Gene E. Lester

The consumption of netted muskmelons (Cucumis melo L. Reticulatus group) has raised health concerns due to pathogenic bacteria attaching to sites on the netted rind inaccessible to sanitation. The purpose of this study was to compare 1) the enzymic and nonenzymic antioxidant capacity between representative cultivars of netted muskmelon and both green- and orange-fleshed honey dew muskmelons during storage for 17 days and 2) levels of non-nutrient phytochemicals between these genotypes in consideration of ultimately substituting netted orange-fleshed with non-netted orange-fleshed muskmelon. Netted muskmelon (`Cruiser'), green-fleshed (`Honey Brew'), and orange-fleshed (`Orange Dew') muskmelons were harvested in Texas at the beginning (21 May) and at the end (11 June) of the production season in 2004. Fruit were analyzed immediately (day 0) or stored simulating retail conditions for 7 or 14 days at 7 °C and 95% ± 2% relative humidity plus 3 days at 21 °C. Both `Orange Dew' and `Honey Brew' non-netted cultivars evinced similar and less lipid peroxidation, and hence postharvest senescence, during the 17-day storage period than the netted muskmelon `Cruiser'. In comparison with `Cruiser', `Orange Dew' generally exhibited higher concentrations of ß-carotene and phenolics and, with few exceptions, higher activities of the antioxidant enzymes ascorbate peroxidase (AsPX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), catalase (CAT), guaiacol peroxidase (POX), and superoxide dismutase (SOD). Higher AsPX and SOD activities in both `Orange Dew' and `Honey Brew' appear to confer a greater resistance to lipid peroxidation in these muskmelon genotypes than to the netted `Cruiser'. `Orange Dew' also appears to be a healthier food choice not only due to its lack of a netted rind which could potentially harbour human illness-related pathogens, but also that it is superior to both `Cruiser' and `Honey Brew' in overall beta-carotene and phenolic levels.

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Gene E. Lester, John L. Jifon and Gordon Rogers

Muskmelon [Cucumis melo L. (Reticulatus Group)] fruit sugar content is directly related to potassium (K)-mediated phloem transport of sucrose into the fruit. However, during fruit growth and maturation, soil fertilization alone is often inadequate (due to poor root uptake and competitive uptake inhibition from calcium and magnesium) to satisfy the numerous K-dependent processes, such as photosynthesis, phloem transport, and fruit growth. Experiments were conducted during Spring 2003 and 2004 to determine if supplemental foliar K applications during the fruit growth and maturation period would alleviate this apparent inadequate K availability in orange-flesh muskmelon `Cruiser'. Plants were grown in a greenhouse and fertilized throughout the study with a soil-applied N-P-K fertilizer. Flowers were hand pollinated and only one fruit per plant was allowed to develop. Starting at 3 to 5 days after fruit set, and up to 3 to 5 days prior to fruit maturity (full slip), entire plants, including the fruit, were sprayed with a glycine amino acid-complexed potassium (potassium metalosate, 24% K) solution, diluted to 4.0 mL·L-1. Three sets of plants were sprayed either weekly (once per week), biweekly (once every 2 weeks) or not sprayed (control). Fruit from plants receiving supplemental foliar K matured on average 2 days earlier than those from control plants. In general, there were no differences in fruit maturity or quality aspects between the weekly and biweekly treatments except for fruit sugar and beta-carotene concentrations, which were significantly higher in the weekly compared to the biweekly or control treatments. Supplemental foliar K applications also resulted in significantly firmer fruit with higher K, soluble solids, total sugars, ascorbic acid (vitamin C) and beta-carotene concentrations than fruit from control plants. These results demonstrate that carefully timed foliar K nutrition can alleviate the developmentally induced K deficiency effects on fruit quality and marketability.