Agriculture Reference
In-Depth Information
susceptible to chilling injury and shrivel (Sherman
et al
.
1987). Unwrapped cantaloupes were considered unmar-
ketable with 6% weight loss (Lester & Bruton 1986). One
consequence of weight loss is not readily apparent.
Hollowneck is a storage disorder in butternut squash
characterized by the gradual development of internal open
areas in the neck; it is not visible externally until it
becomes severe. Hollowneck symptoms become visible
when weight loss exceeds 10% (Francis & Thomson 1964).
Curing (drying) winter squashes at ambient or elevated
temperatures prior to storage did not extend post-harvest
life nor reduce decay, but rather promoted weight loss
(Schales & Isenberg 1963).
During storage at three temperatures, chayote lost the
following fresh weights per day: 25°C: 1.3%, 15°C: 0.5%/
day and 10°C: 0.02% (Aung
et al
. 1996). Wrapping with
polyvinyl chloride (PVC) film reduced weight loss by 80%
to 90% at these same temperatures.
Excessive weight loss during post-harvest handling
leads to fruit softening and greater susceptibility to
mechanical injuries, which in turn facilitates growth of
pathogenic microorganisms in the weakened tissue.
Unwrapped cantaloupe lost 6% fresh weight (40%
softening) during storage, while fruit covered with shrink-
wrapped plastic lost only 0.3% fresh weight and were
considered acceptably firm (Lester & Bruton 1986). In
another study, although shrink-wrapped cantaloupe had
excellent appearance following 21 days storage at 4°C,
trained taste panellists rated flavour and aroma inferior
to that of unwrapped fruit (Collins
et al
. 1990).
Table 14.9
Relative Epidermal and Pulp Firmness
(Bioyield Point) for Selected Cucurbit Fruits.
Fruit type
Skin firmness (N)
z
Pulp firmness (N)
Kabocha squash
60.8
18.6
Pumpkin
51.0
18.1
Chayote
22.1
14.3
Cucumber
20.6
3.7
Zucchini
19.6
5.9
z
Probe: flat-end plunger, 3.2 mm diameter. Crosshead
speed: 25 mm/min.
Source: Aung
et al
. (1996). Reproduced from the
Journal of Horticultural Science
.
texture (Locascio
et al
. 1984). In this same review the
authors also stated that nitrogen deficiency stunts plant
and leaf growth leading to smaller and fewer fruits and
more potential for sunburn in watermelon, and to poor
net formation and a higher percentage of cull fruit in
cantaloupe.
Calcium concentration in cucurbits can be a serious
limiting factor to post-harvest quality. It plays a key role in
maintaining plasma membrane integrity via the cytoplasm,
thus slowing disruption of cellular functions (Lester
et al
.
1998; Lester & Grusak 2001). Cucumbers are not as
susceptible to calcium deficiency as other fruits since the
fruit is the primary sink on the plant (Ho & Adams 1994).
However, under severe conditions, calcium deficiency
appears as water-soaked lesions in the blossom end of the
fruit that later became necrotic (blossom-end rot); carpel
separation from mesocarp tissue that formed air cavities at
the stem end was also observed (Frost & Kretchman 1989).
Fresh pickling cucumbers can develop pillowy fruit disor-
der, characterized by white, porous areas in mesocarp tis-
sue; following fresh-pack pickling process, these areas
appear as water-soaked regions (Thomas & Staub 1992).
This is another calcium-related deficiency induced by
water stress conditions.
Pacheco (1996) reported higher total soluble solids
content and better appearance in 'Galia' fruit with increased
potassium application (applied pre-plant), where 140 kg/ha
was determined as the optimal rate for marketable yield
and fruit size.
Boron deficiency symptoms in Beit Alpha-type cucum-
ber cause small fruits to abort, while on older fruits
symptoms include stunted and curved growth and 'mottled
yellow longitudinal streaks which develop into corky
markings (scurfing) along the skin' these symptoms are
most severe at the blossom end (Cresswell & James, 1998).
Firmness
As apparent from the previous section, fruit firmness is one
of the key factors for marketing fresh produce (Table 14.9).
It is also a reason for harvesting as early as possible without
negatively affecting edible quality so as to extend
post-harvest life to reach more distant markets. Firmness
decreases during handling and storage due to excessive
number and/or intensity of drops, weight loss and meta-
bolic activity.
Plant nutrition and fruit quality
Abiotic disorders can be induced in cucurbit fruits due to
a number of environmental stresses. Nutritional deficien-
cies during growth and development can lead to many dis-
orders. Nitrogen deficiency in the plant causes poor
chlorophyll synthesis in fruits that are prized for intense
green epidermis such as cucumber and zucchini. Nitrogen
deficiency decreases fruit size (yield), but it increases dry
matter content, causing the fruit to have a coarse or tough
