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Drs. Gene E. Lester and Michael A. Grunsak
Cantaloupe, Honeydew Fruit Respond Differently To Chelated Calcium
Two-year study assesses benefits of pre-harvest plant applications during fruit growth and maturation.Summary: Cantaloupe fruit at both locations did not appear to benefit from pre-harvest plant applications of calcium (Ca) when compared to fruit from plants treated with water. Honeydew fruit did, however, and the benefit was both years. Honeydew fruit that received four pre-harvest plant applications of Ca, regardless of source, were generally superior in firmness, marketability, and had a higher Ca concentration than fruit from plants receiving water or one or two applications of Ca. Fruit sugars and taste were not affected by pre-harvest plant applications of Ca.
Post-harvest dipping fully ripened honeydew melons in organic chelated Ca versus EDTA-chelated Ca or Ca chloride (CaCl2) solutions has been shown to maintain stored honeydew fruit Ca concentration at levels found in recently abscised fruit, thus maintaining fruit tissue firmness, plasma membrane integrity, and extending storage life. However, applying Ca to commercially grown melons as a post-harvest dip is not suitable for melon growers in the desert southwestern U.S. or other low-humidity melon growing regions of the U.S. These growers box melons for shipment in the field at harvest, making a post harvest dip impractical.
Although application of Ca to melon fruit tissue disks, greenhouse grown melons, or commercially harvested melons has been reported, no studies have been reported during fruit production for pre-harvest plant application of organic-chelated Ca sources to commercial fields of either honeydew or netted cantaloupe.
Table 1. Firmness of ‘Orange Dew’ orange-flesh honeydew melon exterior with peel removed (exterior) and edible-flesh (interior) at harvest and following commercial storage, Sacramento Valley, CA. Fruit harvested at abscission in Sept. 2001 and 2002.
Table 2. Calcium concentration of ‘Orange Dew’ orange-flesh honey dew melon exterior with peel removed and edible-flesh (interior) at harvest and following commercial storage, Sacramento Valley, Calif. Fruit were harvested at abscission in Sept. 2001 and 2002.
Table 3. Calcium concentration of ‘Sol Real’ (Calif.) and ‘Primo’ (Texas) orange-fleshed netted cantaloupe, with peel removed (exterior) and edible-flesh (interior) at harvest and following commercial storage. Imperial Valley, CA, and the Rio Grande Valley, TX, 2002.
Table 4. Marketability of ‘Sol Real’(Calif.) and ‘Primo’ (Texas) orange-fleshed netted cantaloupe, with peel removed (exterior) and edible-flesh (interior) at harvest and following commercial storage, Imperial Valley, Calif., and the Rio Grande Valley, Texas, 2002.
Honeydew melons
Firmness. In 2001 and 2002, four applications of amino acid chelated Ca (AA-Ca) or mannitol-complexed Ca (MC-Ca), versus control applications of water, resulted in significantly firmer readings of the fruit exterior tissues under the peel at harvest (Table 1). Fruit interior (edible tissue) firmness readings in 2001 from four applications of AA-Ca or MC-Ca and only AA-Ca in 2002, versus water, resulted in significantly firmer edible tissue. One or two applications of either Ca compound, applied at female flowering and/or within 20 days after flowering (early applications) or within 40 days after female flowering and/or within 3 to 5 days before abscission (late applications), were not always significantly better than water in affecting exterior or interior fruit firmness. Following storage of melons for 2 or 3 weeks, exterior and interior firmness were generally significantly firmer with four applications of either plant-applied Ca compound, than those receiving one or two early or late Ca applications of water.
Ca. In 2001 and 2002 four applications of AA-Ca or MC-Ca (versus water) resulted in significantly higher Ca concentrations in fruit exterior and interior tissues at harvest (Table 2). One or two early or late applications of either Ca compound were not always significantly higher in Ca than water. In both years, fruit from four applications of Ca stored for two weeks had higher exterior and interior Ca concentrations than water. After three weeks, for both years, fruit from four applications of Ca were significantly higher in tissue (exterior and interior) Ca concentrations than those treated with water.
Marketability. Following two or three weeks of storage, exterior and interior percent marketability of fruit from plants receiving four applications of AA-Ca or MC-Ca, versus water, were for most comparisons significantly greater. Also, one or two applications of Ca applied early or late, when compared to water, were significantly greater in exterior and interior marketability for most comparisons.
Sugars and taste. Percent soluble solids concentration for all fruit was similar within each production year, regardless of Ca source or number of applications. Sugars were lower by about 2.8 percent in 2002 versus 2001. With few exceptions, consumer preference for all fruit ranged from like to like extremely. Consumers usually gave fruit from water-treated plants the best taste ratings, but fruit from the water treatments generally were not significantly better than fruit from plants receiving Ca treatments. Only a few of the Ca treatments resulted in fruit with significantly lower ratings, relative to water-treated controls
Cantaloupe melons
Firmness. At harvest, whether grown in California or Texas or having received pre-harvest plant-applied Ca treatments or water, exterior or interior firmness readings were not consistently, significantly different. Following one or two weeks storage, fruit exterior or interior tissues from plants receiving applications of Ca were usually not significantly firmer than those from the water treatment
Ca. At harvest, whether grown in California or Texas, Ca concentration was usually numerically the highest in both exterior and interior fruit tissues from plants having received four applications of AA-Ca (Table 3), but the concentrations were not significantly higher in fruit from the water treatment. Following one or two weeks storage, fruit exterior and interior tissues from plants having received four applications of AA-Ca remained numerically the highest in Ca and generally were significantly higher than water. However, all other Ca treatments usually were not significantly higher than water.
Marketability. Following one week of storage, exterior and interior percent marketability of fruit from plants receiving Ca versus water was not significantly different. Following two weeks storage, Texas-grown fruit exterior and interior marketability from plants receiving Ca applications was significantly better than water (Table 4). But in California-grown fruit, Ca treatments (versus water) were not statistically different for either exterior or interior percent marketability.
Sugars and taste. Percent soluble solids concentration, within each growing location for all fruit was similar. Between locations the concentration of sugars was lower in Texas than California-grown fruit. With few exceptions, consumer preference for all fruit, regardless of location, ranged from like to like extremely. Statistically, significant differences were observed between certain treatments, but across all locations or storage times, no treatments were consistently different. Consumers usually gave fruit from Ca-treated plants the best rating, but it was never always significantly better than fruit from plants receiving water.
Dr. Lester is research plant physiologist, USDA-ARS, Kika de la Garza Subtropical Agricultural Research Center in Weslaco, TX, and Dr. Grusak is research plant physiologist, USDA-ARS, Children’s Nutrition Research Center, Houston, TX.