Preharvest Foliar Calcium Treatments for Reduction of Postharvest Myrothecium Fruit Rot of Muskmelon

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Cucurbit Genetics Cooperative Report 17:78-80 (article 22) 1994

J.O. Kuti and E.C. Boehm
Department of Agronomy & Resource Sciences, Hort. Crops Research Lab., Texas A&M University-Kingsville, TX 78363, USA

Muskmelons (Cucumis melo L.) are perishable horticultural commodity with variable storage lifes depending on the botanical variety. For example, honeydew and casaba melons (C. melo var. indorus) tend to be less perishable than netted melons (C, melo var. reticulatus) (8). Muskmelon decline in storage is usually manifested by flesh softening and breakdown which often lead to postharvest decay (6). Many postharvest fruit rots arise as quiescent or latent infection in the field or as a result of injuries during harvesting and handling operations which subsequently lead to infection from fungal spores. Myrothecium roridum Tode ex. Fries is one of the major preharvest and postharvest pathogens of muskmelon (1). Myrothecium fruit rot of muskmelon can occur in the field, in transit to the market, during marketing or in consumer refrigerators (3).

Many studies have shown that increasing calcium content of fruits may extend storage life by delaying fruit ripening and senescence (2), and by maintaining firmness (4). The slower decline in flesh firmness of ripening fruit have been attributed to ability of calcium ions (Ca++) to combine with pectin to form calcium pectate in cell walls (10). Calcium enhances host resistance to fungal infection by strengthening or stabilizing the cell walls, thus preventing cell wall breakdown by pathogens (9). This study was initiated to determine the effect of preharvest foliar application of calcium on susceptibility of muskmelon to Myrothecium storage rot.

Two botanical varieties of muskmelon were used. One botanical variety is a honeydew melon ‘Limelight’ (Burpee Seed Co.) and the other is a netted melon ‘Tam Uvalde’ (Wilhite Seed Co.). Both melon varieties were grown under identical conditions in Kingsville, Texas. At about 28 days postanthesis, fruits were sprayed over a six week period (i.e., at 2-week intervals) with calcium, Nutrical(R), a complex of calcium (8%) and an organic chelating agent – trihdroxyglutarate (CSI Chemical Corp., Boudurant, IA), at the rates of 0, 0.5, 1.0 and 1.5 1 ha-1 using a high-pressure hand gun sprayer. Developing fruits were sprayed until run-off. Treatments were assigned to 2-row plots in a completely randomized design and replicated 3 times. The honeydew melons were harvested at 84 days postanthesis and the netted melons harvested when abscission layer was evident. Five fruits were randomly selected from each of the treatments, weighed and assessed for soluble solids and flesh firmness. Flesh calcium of fruits from each treatment was also determined by atomic absorption spectrophotometry.

Fruits were inoculated with 25 1 spore suspensions of M. roridum (ATCC# 52485) at 4 sites around the fruit equatorial region using a modified multiple puncture inoculation technique as described by Reed and Stevenson (7). Inoculated fruits were covered with a larger perforated polyethylene sheet to prevent dehydration and incubated under ambient storage conditions (25 2˚C and 85% RH). Fruit decay volume was measured 14 days after inoculation by measuring surface area of decay and multiplying by the depth of decay. There were 5 fruits per calcium treatment for each melon in the botanical types. Inoculated fruits without Nutrical (R) application served as controls. All experiments were repeated at least twice and data were analyzed by analysis of variance procedures.

Results of fruit weight, firmness, soluble solids, flesh calcium content, and Myrothecium decay of inoculated fruits are shown in Table 1. Low calcium treatments resulted in lower flesh firmness and calcium content in both botanical varieties of muskmelon tested. By increasing flesh calcium concentration, decay severity by M. roridum was significantly reduced only in the honeydew melons, while the netted melons showed no difference. Calcium treatments did not affect the fruit weight of both melon types. While honeydew melons treated with calcium had higher soluble solids than untreated melons, netted melons treated with calcium had lower soluble solids when compared to the untreated controls. the differences in flesh calcium content of honeydew melons and netted melons in this study are consistent with previous findings of Ng and Carr (5).

The results of the present study indicate that foliar treatments of honeydew melons with Nutrical (R) or any other absorbable calcium salts may have the potential to reduce storage losses due to postharvest pathogens and may provide high quality melon for the consumer.

Table 1. Effect of foliar calcium treatments on fruit weight, firmness, soluble solids and flesh calcium content and susceptibility to Myrothecium fruit rot of two botanical varieties of muskmelon (honeydew melon, ‘Limelight’ and netted melon, ‘Tam Uvalde’).

Treatment (Nutrical(R))

Weight

(kg)

Firmness

(kg)

Solids

(%)

Ca ++ content

( μ g g-1 fw )

Decay volz

(cm3 )
Honeydew Melon ‘Limelight’
Control 1.53 ay 12.6 a 9.8 a 1.19 a 6.4 a
0.5 1 ha-1 1.67 a 13.1 b 12.6 b 2.60 b 5.7 b
0.01 1 ha-1 1.64 a 18.2 c 12.8 b 3.89 c 3.2 c
1.51 1 ha-1 1.69 a 19.6 d 12.6 b 4.28 d 0.9 d
Netted Melon ‘Tam Uvalde’
Control 0.83 a 14.3 a 12.0 a 0.76 a 5.6 a
0.5 1 ha-1 0.87 a 14.7 a 10.2 b 0.94 b 5.2 a
1.01 1 ha-1 0.87 a 15.6 b 9.8 b 1.21 c 5.0 a
1.51 1 ha-1 0.86 a 15.6 b 9.6 b 1.43 d 4.7 a

z Decay volume was determined by measuring surface area of decay and then multiplying by the depth of decay.
y Mean separation in the columns by Duncan’s multiple range test (P = 0.05).

Literature Cited

  1. Bruton, B.D. 1982. Myrothecium roridum a probably devastating pathogen of muskmelon in south Texas. Phytopathology 72:355 (Abstr.).
  2. Ferguson, I.B. 1984. Ca2+ in plant senescence and fruit ripening. Plant Cell Env. 7:477-489.
  3. Kuti, J.O., T.J. Ng, and G.A. Bean. 1986. Influence of genotype and soluble solid content on resistance of muskmelon fruits to preharvest infection by Myrothecium roridum Tode ex. Fries. HortScience 21:367 (Abstr.).
  4. Mason, j.L. 1976. Calcium concentration and firmness of stored ‘McIntosh’ apples increased by calcium chloride solution plus thickener. HortScience 11:504-505.
  5. Ng, T.J. and V. Carr. 1989. Fresh calcium content of group inodorous and group reticulatus muskmelon (Cucumis melo L.) fruit. Cucurbit Genet. Coop. 12:53-54.
  6. Pratt, H.K., J.D. Goeschl, and F.W. Martin. 1977. fruit growth and development, ripening and role of ethylene in ‘Honey Dew’ muskmelon. J. Amer. Soc. Hort. Sci., 102:203-210.
  7. Reed, G.L. and C. Stevenson. 1982. Methods for inoculating muskmelon with Erwina trachephilla. Plant Disease 66:778-780.
  8. Ryall, A.L. and W.J. Lipton. 1972. Handling, Transportation and Storage of Fruits and Vegetables. Vol. 1, AVI Publishing Co., Inc. Westport, CT.
  9. Sharples, R.O. and D.S. Johnson. 1977. The influence of calcium on senescence changes in apples. Ann. Appl. Biol. 85:450-453.
  10. Tepter, M. and I.E.P. 1981. The interaction of divalent cations with pectic substances and their influence on acid induced cell wall loosening. Can. J. Bot. 59:1522-1525.