Flesh Calcium Content of Group Inodorus and Group Reticulatus Muskmelon (Cucumis melo L.) Fruits

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Cucurbit Genetics Cooperative Report 12:53-54 (article 23) 1989

Timothy J. Ng and Vermal Carr
University of Maryland, Department of Horticulture, College Park, MD 20742-5611

Honeydew and casaba (group Inodorus) muskmelons tend to have extended storage lives when compared to netted (group Reticulatus) muskmelons (5). Decline in storage is usually manifested by flesh softening and breakdown, and by shriveling and discoloration of the rind. Genetic differences in storage life may be attributable in part to differences in the timing and magnitude of the ethylene climacteric in the different types of muskmelons (2, 4).

Calcium may also be involved in regulating ripening in muskmelons. Higher calcium concentrations can retard ripening and senescence activities in many climacteric fruit tissues (1). The slower decline in flesh firmness of ripening fruits with higher calcium concentrations has been attributed to the ability of calcium to combine with pectin to form a calcium pectate in cell walls (3). The current study was initiated to determine whether differences in flesh calcium concentrations existed among different types of muskmelons, and whether these differences might be related to fruit longevity in storage.

Two casaba, two honeydew and two netted cultigens of muskmelon were grown under identical conditions in Salisbury, Md. Six ripe fruits of each cultigen were harvested on the same day. ripeness was determined on netted types by abscission of the fruit from the vine, while ripeness of honeydew and casaba melons was determined by fruit softening at the blossom end. Fruits were transported back to College Park, Md., and three fruits of each cultigen were sampled immediately for percent dry weight and flesh calcium content. The remaining three fruits were stored for 7 days at 10°C and 95% RH, then sampled. For calcium determinations, ashed tissue samples were dissolved in boiling 5N HCl, filtered, and subjected to atomic absorption and emission spectrophotometry.

Flesh dry weight and calcium concentration for the six cultigens are presented in Table 1. The analyses of variance for the effects of muskmelon type and storage on dry weight and calcium content are presented in Table 2. Percent dry weight was similar among the different fruit types but increased during storage, probably as a result of fruit dehydration. Calcium, on both a fresh and dry weight basis, was significantly affected by muskmelon type. However, the casaba cultigens, which have the longest storage life, had the lowest calcium concentrations. In particular, the casaba ‘MaryGold’, which can be stored for over two months in a marketable state (personal observation), had the lowest calcium concentration among all lines. Honeydew, which are intermediate in storage ability between casaba and netted types, had the highest calcium concentration.

Although this study was preliminary in nature, it seems unlikely that major differences in the rate of fruit ripening and senescence among group Inodorus and group Reticulatus muskmelons can be simply explained on the basis of flesh calcium content.

Table 1. Flesh dry weight and calcium content in honeydew, casaba and netted muskmelons at harvest or stored for 7 days at 10°C.

Dry Weight (% fw)

Flesh Calcium Content
μg Ca/g fw
μg Ca/g dw

Muskmelon type
Line
Fresh
Stored
Fresh
Stored
Fresh
Stored
Casaba MD8562 0.14 0.14 1.07 0.91 7.82 6.78
MaryGold 0.13 0.14 0.85 0.91 6.55 6.44
Honeydew MD85100 0.13 0.15 1.46 1.26 11.54 8.50
MD8599 0.13 0.14 1.40 0.88 10.90 6.70
Netted MD8540 0.12 0.13 1.05 1.02 8.55 8.17
MD266 0.12 0.15 1.15 1.02 8.52 6.73

Table 2. ANOVA for effect of muskmelon type on dry weight and calcium.

Dependent variable

Muskmelon type

Storage
Flesh dry weight NS *
Calcium (fw basis) * NS
Calcium (dw basis) * *

NS, * indicate not significant, and significant at the 5% level.

Literature Cited

  1. Ferguson, I.B. 1984. Ca2+ in plant senescence and fruit ripening. Plant Cell Env. 7:477-489.
  2. Kendall, S.A. and T.J. Ng. 1988. Genetic variation of ethylene production in harvested muskmelon fruits. HortScience 23:759-761.
  3. Legge, R.L., J.E. Thompson, J.E. Baker and M. Liederman. 1982. The effect of calcium on the fluidity and phase properties of microsomal membranes isolated from post-climacteric Golden Delicious apples. Plant and Cell Physiol. 23:161-169.
  4. Pratt, H.K., J.D. Goeschl, and F.W. Martin. 1977. Fruit Growth and development, ripening, and the role of ethylene in the ‘Honey Dew’ muskmelon. J. Amer. Soc. Hort. Sci. 102:203-210.
  5. Ryall, A.L. and W.J. Lipton. 1972. Handling, Transportation, and Storage of Fruits and Vegetables. Vol. 1: Vegetables and Melons. AVI Publishing Co., Inc. Westport, CT.