Cucumis melo varieties show a great diversity of ripening and abscission phenotype, ethylene production, and postharvest keeping quality. As a preliminary step in the development of melons with improved shelf-life and modified ripening, we surveyed 100 genotypes of melons with diverse ripening characteristics for ethylene production rate and shelf-life. Genotypes representing seven melon types (Western shipper cantaloupes, Eastern cantaloupes, Long shelf life cantaloupes [LSL], Charenteis, Galias, Honeydews, Casabas) were planted in the field in a randomized complete block with three replications. C. melo var. reticulatus and C. melo var. inodorus were harvested 40 and 50 days post-anthesis, respectively, and brought in the lab for ethylene production measurement. Fruit at horticultural maturity were also harvested and stored at room temperature. After 7 days, a postharvest decay rating (1 = complete rot and collapse–5 = no softening or decay) was taken to determine relative shelf-life of the genotypes. Average ethylene production rate ranged from 44.44 to 0.64 nl·h–1·g–1 for Eastern cantaloupes and Casaba melons, respectively. A negative linear relationship was observed between ethylene production rate and postharvest decay rating. LSL cantaloupes had the lowest ethylene production rate of the netted, orange flesh types. The relationship between ethylene production rate and polymorphism for ACC oxidase (pMEL1) and ACC synthase (pMEACS1) cDNA probes is being investigated.
Poor germination of lettuce seeds exposed to heat and salinity is attributed to a reduction in the capacity for embryo expansion. Ethylene and kinetin are proposed to overcome these stresses by increasing the expansion force of the embryo which ruptures the seed coat barrier to growth. To better understand the physiological mechanism regulating thermodormancy in the embryo, germination was determined for intact and decoated seeds from thermosensitive and thermotolerant varieties subjected to a critical range of temperature and salt (NaCl) stress. Although more tolerant of stress, the response of decoated seeds to ACC and kinetin was similar to the response of intact seeds. No interaction between ACC and kinetin was detected in decoated seed except under the most severe stress and in the thermosensitive variety. Heat and salt tolerance appear to be governed by the same physiological mechanism. We propose that the seed coat plays no qualitative role in the expression of lettuce seed thermodormancy. The response occurs exclusively in the embryo and may result from an inability to generate sufficient turgor pressure at supraoptimal temperatures for cell expansion.
Exposure of muskmelon (Cucumis melo L. Group reticulatus) fruit to high temperatures at harvest causes sunbuming, decreases firmness, lessens overall quality (2), and may accelerate fresh weight loss. The purpose of this study was to examine the effect of high prestorage temperatures on muskmelon fresh weight loss and on relative storage life measured as electrolyte leakage of shrink-film wrapped and nonwrapped fruit.
Seedling transplants produced for early fall and spring establishment of commercial vegetable crops in the Texas Lower Rio Grande Valley rapidly develop excessive shoot growth if field plantings are delayed. Therefore, several varieties of pepper, watermelon, muskmelon, and tomato transplants were treated at the 2-3 leaf stage by foliar spray with 0, 4, 8, or 12 ppm of the triazole growth retardant, uniconazole. The seedlings were field transplanted 3 weeks later. Total heights taken at the time of transplanting indicated significant varietal differences in responses to the treatments. After 60 days in the field, one of the 5 pepper varieties continued to express retarded growth. However, the uniconazole treatment stimulated early fruiting in 2 of the varieties. Tomato seedlings appeared to overcome the stunting within the first 60 days after transplanting while muskmelon and watermelon remained slightly dwarfed. Additional data on total growth and yield in response to the growth retarding treatments will be presented for each of the vegetable varieties.
Postharvest ethylene production and ACC levels were determined in netted muskmelon fruits (Cucumis melo L. var. reticulatus `Magnum 45') exposed to temperature extremes by heating for 3 hr at 45C and/or storage at 4C. The possibility of using seal-packaging to protect the fruit against temperature-induced changes in ethylene production was examined by wrapping melons before treatment with a high-density polyethylene (HDPE) shrink-film. Ethylene production measured in fruit immediately after heating or removal from refrigeration was only 30% of the level determined before treatment, and continued to decline during refrigerated storage. However, the concentration of ACC in these same tissues remained constant or even increased slightly during storage. Wrapping fruit in HDPE film had no effect on the tissue concentrations of ACC or capacity for ethylene synthesis. In contrast to initial measurements, heated or refrigerated fruit held at room temperature (25C) for 24 hr produced ethylene at rates that equalled or exceeded the levels for freshly harvested fruit. These results strongly suggest that temperature-imposed restrictions on ethylene synthesis by netted muskmelon fruit are reversible and occur at the step responsible for converting ACC to ethylene via EFE rather than in the synthesis of ACC. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC).
Postharvest sugar content and activities of four enzymes of sucrose metabolism were followed in the edible mesocarp tissue of the netted muskmelon (Cucumis melo L., var. reticulatus, cv Magnum 45). Melons harvested at full-slip were shrink film-wrapped to inhibit water loss and/or heated to 45°C for 3 hr before storage at 4°C for up to 18 days. Sucrose content of edible mesocarp remained constant between harvest and 12 days of storage. The sucrose content of nonheated fruit declined between 12 and 18 days of storage, but there was no coincident increase in glucose or fructose. There was little acid invertase activity. Neutral invertase activity did not vary significantly with storage, but was slightly higher in heated, wrapped fruit than in nonheated, wrapped fruit. Sucrose synthase activity increased with storage, and was higher in heated than nonheated fruit. There was no discernible pattern of sucrose-phosphate synthase activity. No enzyme activity was correlated with the content of any sugar.