Post harvest diseases fruits and vegetables - Xavier University ...

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
248 Postharvest Diseases of Fruits and Vegetables
The integration of postharvest biocontrol into modern production,
storage and handUng systems must begin before harvest. Several
preharvest factors that affect fruit quahty may have profound effects on
the efficacy of postharvest biological control agents (Roberts, 1994).
Preharvest calcium sprays during the growing season of apples and
pears, as well as calcium application by immersion infiltration at
postharvest, can increase fruit firmness, decrease the incidence of certain
disorders and enhance resistance to postharvest infection (see the
chapter on Means for Maintaining Host Resistance - Calcium
Application). As was previously mentioned, calcium amendments and
postharvest application of some antagonistic yeasts can be additive in
reducing fruit decay and can significantly increase disease control
compared with either treatment alone (McLaughlin et al., 1990; Droby et
al., 1997). The advantages in increased firmness, enhanced resistance to
postharvest decay and enhanced biocontrol efficacy under some
circumstances reflect the multiple benefits of integrating postharvest
biological control with cultural and production practices (Roberts, 1994).
Fruit maturity at harvest and at the application of antagonists is
another factor affecting postharvest biological control. Late-picked,
over-mature fruits are more susceptible to decay than are fruits picked at
optimal storage maturity (Sommer, 1982). Working with apples and
pears, and with different species of the antagonistic yeast Cryptococcus,
Roberts (1990, 1994) found that fruit maturity markedly affected
biocontrol efficacy: while excellent control was achieved on freshly
harvested fruit, treatments of ripened fruit gave much lower levels of
control. On the assumption that the infection process can be initiated at
harvest, it would be advantageous to treat fruit with biocontrol agents as
quickly as possible after harvest and to cool the fruit as rapidly as
possible, to retard pathogen development. In fact, studies with
Mi/cor-inoculated pears and antagonistic Cryptococcus species
demonstrated maximal biocontrol effect when the yeasts were applied to
the fruit soon after harvest (Roberts, 1990). The principle is to retard
pathogen development while allowing the antagonistic microorganisms to
colonize wound sites.
Postharvest factors, too, may have a major impact on the effectiveness
of biological control. Temperature management, which is a critical factor
in the maintenance of fruit quality and in pathogen development (see the
chapter on Factors Affecting Disease Development), may also enhance
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