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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
262 Postharvest Diseases of Fruits and Vegetables
rot caused by P. digitatum progressed through an apple and came into
contact with a damaged region, it developed around the damage site
leaving a halo of uninfected tissue. This area was suggested to be the
location in which the host defense reaction occurred (Wild and Wilson,
1996).
In a recent study, Ippolito et al. (2000) found that the antagonistic
yeast-like fungus, Aureobasidium pullulans multiplied rapidly in apple
wounds, and reduced decay incidence in apples inoculated with Botrytis
cinerea and P. expansum. However, they also found that the antagonist
was capable of inducing the activities of P-l,3-glucanase, chitinase and
peroxidase in the treated wounds on the fruits. This induction was
exhibited in a transient increase in the enzymatic activity which started
24 h after the application of the antagonist, and reached a maximum 48
or 96 h after the treatment. The three enzymes are considered to be
potentially important in host resistance mechanisms: chitinase and
P-l,3-glucanase are hydrolases, capable of hydrolyzing fungal cells
(Schlumbaum et al., 1986; Wilson et al., 1994), while peroxidase is
involved in lignin formation and the production of structural barriers
against pathogens (El Ghaouth et al., 1998; Chittoor et al., 1999). It was
thus suggested that the induced activity of the glucano-hydrolases and
peroxidase, together with the capacity to out-compete the pathogen for
nutrients and space may be the basis of the biocontrol activity of
A pullulans (Ippolito et al., 2000).
B. GENETIC MODIFICATION OF PLANTS
1. DISEASE-RESISTANT TRANSGENIC PLANTS
Genetic transformation of plants for desired traits - such as improved
yield, increased size or enhanced disease resistance - is not a new
concept. Classical breeding has always provided new plant varieties
which have desirable characteristics. However, the process can be too
slow and inexact. Often pathogens can mutate too quickly for breeding of
disease resistance varieties by classical methods. Progress in the
development of bioengineering techniques provided the opportunity to
modify plants, and enabled new transgenic plants with greater disease
resistance to be developed more rapidly than via classical methods
(Mount and Berman, 1994). A transgenic plant contains, within its
genome, a foreign DNA that has been introduced artificially via genetic
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