Cucurbits - Crop Post-Harvest: Science and Technology - page 334

Table 14.10 Principal Post-harvest Diseases of Cucurbits.
Common name

Organism Commonly affected crops

Alternaria rot Alternaria alternata Cucurbits

Anthracrose Colletorichum orbiculare Cucurbits

Bacterial soft rot Erwinia caratorona Cucurbits

Belly rot Rhizoctonia solani Cucumber

Black rot Didymella bryoniae Winter squash

Blue mold Penicillium spp . Cucumber, melon

Choanephora rot Choanephora cucurbitarum Summer squash

Cottony leak Pythium spp . Cucurbits

Fusarium rot Fusarium spp . Cucurbits

Phytophthora rot Phytophthora capsici Cucurbits

Rhizopus rot Rhizopus stolonifer Cucurbits

Scab Cladosporim cucumerinum Cucurbits

Sclerotinia rot Sclerotinia sclerotiorum Cucurbits

Southern blight Sclerotinia rolfsii Cucurbits

Source: Snowdon (1992) and Zitter et al . (1996).

cucumber. This has been attributed to stimulation of
peroxidase activity. Miller and Kelly (1989) reported a
positive correlation between peroxidase activity and
bruise severity in pickling cucumbers; mesocarp and carpel
tissues also became water-soaked. Transmission electron
microscopy revealed cellular disorganization in bruised
cucumbers after 48 hours of storage at 23°C (Abbott et al .
1991). The authors noted the disappearance of starch gran-
ules and appearance of dense inclusions in chloroplasts
from bruised fruits.
Compression bruising of packed fruits is a common
problem during handling and shipping. It is caused by
constant force exerted on the fruit due to excessive weight
in the package or pressure from the lid from overfilling
of the package, protrusions on inner package surfaces
(Figure 14.17b), and variable firmness of individual fruits
in which case firmer fruits gradually deform softer fruits
over time.
Harvest maturity affects resistance to physical impacts
and compression in cantaloupe. Muskmelon harvested at
full-slip withstood up to 120 cm drop onto a conveyor belt,
while half-slip harvested fruit were less resilient and
bruised or cracked when dropped 90 cm (Foster et al . 1979).
Abrasion and cuts promote moisture loss by removing
epicuticular wax and by creating ports of entry for decay
organisms. Puchalski and Brusewitz (1996) developed a
procedure for quantifying the pulling force necessary to

abrade the surface of a watermelon and determined that
epicuticular wax was removed at approximately 12 N, and
upper layers of the pericarp were removed at about 13 N.

Plant Diseases
Plants must be maintained healthy and adequate disease
control strategies must be followed to minimize fruit dis-
eases in the field and the development of latent infections
during handling and shipping. Major and minor diseases
(Table 14.10) are thoroughly described in Zitter et al .
(1996) and Snowden (1992).
Post-harvest decay control is limited because few
fungicides are registered. Currently, only thiabendazole
(TBZ) is approved for post-harvest application to canta-
loupe (Adaskaveg et al . 2002). Sanitation is one of the
primary means for minimizing pathogen build-up during
harvest and handling operations and will be discussed in
greater detail in the following section. Other treatments
have been successful in reducing disease. Addition of
silicon to nutrient solution in greenhouse-grown cucum-
bers in British Columbia was found to increase the
plants' resistance to powdery mildew (Samuels et al .
1993). However, excess silica that accumulated in
trichomes and epicuticular wax resulted in a noticeably
rougher epidermis and duller appearance. Despite these
slightly negative effects this practice has been widely
adopted in that industry.