Production Practices and Quality Assessment of Food Crops. Vol. 1
Production Practices and Quality Assessment of Food Crops. Vol. 1
Production Practices and Quality Assessment of Food Crops. Vol. 1
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24 R. M. Madakadze <strong>and</strong> J. Kwaramba<br />
4.1.13. Blossom drop<br />
Yellowing <strong>of</strong> pedicels <strong>and</strong> calyx leads to the abortion <strong>of</strong> the flower. This may take<br />
place before or after anthesis. The flower withers <strong>and</strong> turns brown but does not<br />
abscise. Stress conditions increase the incidence <strong>of</strong> the disorder. Any factor that<br />
inhibits, pollination <strong>and</strong> fertilization for example low or high temperature, high<br />
relative humidity, excess wind lead to blossom drop. Improper nutrition from<br />
deficiencies in fertilizer or excess nitrogen tends to also increase the problem. Foliar<br />
diseases <strong>and</strong> insect damage are some documented causes.<br />
4.1.14. Zippering<br />
Very thin longitudinal brown necrotic scars start at the stem scar <strong>and</strong> extend part<br />
or all the way to the blossom end. These long scars have small transverse scars along<br />
them resembling a zipper. Mostly one scar occurs per fruit but there can be several,<br />
at times a hole open at the locule forms in addition. Under cool weather the anthers<br />
may be attached to the ovary wall <strong>of</strong> newly forming fruits causing zippering. Other<br />
weather conditions may also be involved however, susceptibility differs with<br />
cultivars.<br />
4.2. Squash<br />
4.2.1. Chilling injury<br />
Chilling injury is caused if squashes <strong>and</strong> pumpkins remain in the field at<br />
10–12.5 °C or are stored below that temperature. Symptoms <strong>of</strong> chilling injury are<br />
sunken pits on the surface <strong>and</strong> high levels <strong>of</strong> decay (Cantwell <strong>and</strong> Suslow, 2001).<br />
Severe pitting <strong>and</strong> slight decay were observed after 12 days <strong>of</strong> exposure to low<br />
temperature (Wang, 1993). The plants may be severely injured <strong>and</strong> maturity delayed<br />
by temperatures below 5 °C for several days.<br />
In squash (Cucurbita moschata) the severity <strong>of</strong> chilling injury in fruits stored<br />
at 4 °C was reduced by dipping in 1% CaCl 2 or 10 mM sodium benzoate at 20 °C<br />
for 30 minutes. Fruits treated with sodium benzoate showed a low incidence (< 10%)<br />
<strong>of</strong> chilling injury following 30 d <strong>of</strong> storage at 4 °C (Lee <strong>and</strong> Yang, 1999). The<br />
severity <strong>of</strong> chilling injury in Cucurbita pepo (cv Elite) fruits stored at 5 °C <strong>and</strong><br />
then transferred to 20 °C was reduced by a pre storage treatment with hot water<br />
at 42 °C for 30 minutes (Wang, 1993). Chilling injury was further reduced when<br />
fruits were preconditioned at 15 °C for 20 days after hot water treatment but before<br />
5 °C storage.<br />
In Zucchini squash (Cucurbita pepo) post harvest treatments that reduce chilling<br />
injury (temperature conditioning <strong>and</strong> low O 2 storage) were found to increase endogenous<br />
levels <strong>of</strong> polyamines (Wang, 1993). Exogenous treatment with polyamines<br />
by pressure infiltration was shown to increase the tolerance <strong>of</strong> squash to chilling<br />
injury. Both low O 2 storage (1% O 2) <strong>and</strong> temperature conditioning (2 days at<br />
10 °C followed by storage at 2.5 °C) treatments were effective in delaying the<br />
development <strong>of</strong> chilling injury symptoms. Temperature conditioning reduced the
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