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

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Biological Control 241
ammonia lyase (PAL). The involvement of these processes in the
enhanced defense mechanisms in citrus fruit has previously been
described by G.E. Brown and Barmore (1977) in tangerines inoculated
with C. gloeosporioides.
Candida famata (isolate F35) was found to be one of the most active
yeasts tested against P, digitatum in citrus fruits: it was able to reduce
decay by 90-100% in artificially wounded fruits (Arras, 1996). Scanning
electron microscope observations revealed a rapid colonization of the
fungal mycelium at the wound sites, with numerous yeast cells strongly
attached to the hyphae, exhibiting lytic activity and rapid alterations.
Furthermore, when the yeast was inoculated into artificial wounds,
either alone or with the pathogen, it stimulated the fruit to produce the
phytoalexins, scoparone and scopoletin at the wound site. The
concentrations of the phytoalexins depended significantly on the time lag
between inoculation with the antagonist yeast and inoculation with the
pathogen. Four days after inoculating the fruit with the yeast alone,
scoparone concentration reached 124|ig gi fresh weight, 12 times higher
than that in the non-inoculated wound. The concentration reached only
47|xg gi when the antagonist was inoculated together with the pathogen,
and only 37|Lig g^ when the pathogen alone was introduced into the
wounds. Since scoparone inhibits spore germination of P. digitatum at
46 ng g-i and germ tube elongation at 29^g g^ (Kim et al., 1991), it was
concluded that the phytoalexin had already reached fungitoxic
concentrations within a few days of the application of the antagonistic
yeast (Arras, 1996).
Increased resistance to infection can result not only from enhanced
production of phytoalexins but also from preformed inhibitory
compounds. It was thus found that a non-pathogenic mutant of
Colletotrichum magna was capable of enhancing the preformed
antifungal diene compound in avocado fruit peel and could, therefore,
protect the fruit against infection by C. gloeosporioides (Prusky et al.,
1994).
Recently, Ippolito et al. (2000) related the capability of the
antagonistic yeast-like fungus, Aureohasidium pullulans to control decay
in apple fruits inoculated with B, cinerea and P. expansum to its ability
to enhance the activities of the enzymes, p-l,3-gluconase, chitinase and
peroxidase in the treated fruits, in addition to its capacity to overcome
the pathogen in competition for nutrients and space. These enzymes are
all considered to be involved in host defense mechanisms. Chitinase and
P-l,3-gluconase are capable of hydrolyzing fungal cells and so inhibiting
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