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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
70 Postharvest Diseases of Fruits and Vegetables
digitatum, S. sclerotiorium and F, oxysporum (Lattanzio et al., 1995).
The principal phenols in the peach fruit epidermis and subtending cell
layers are chlorogenic and caffeic acids. The concentrations of these
phenols decline as fruits mature, with a corresponding increase in fruit
susceptibility to the brown rot fungus Monilinia fructicola. The levels of
chlorogenic and caffeic acids are higher in peaches with a high level of
resistance than in fruits of similar maturity, of more susceptible
genotypes (Bostock et al., 1999). Studying the direct effects of chlorogenic
and caffeic acids on M fructicola growth indicated that fungal spore
germination or mycelial growth were not inhibited by concentrations
similar to or exceeding those that occur in the tissue of immature,
resistant fruit. Examination of the effects of phenolic compounds on other
factors that may be involved in pathogenicity of the fungus showed that
the presence of either of these phenolic acids in culture during fungal
growth resulted in a sharp decrease in cutinase activity. It was further
proposed that the high concentration of chlorogenic acid present in
immature fruit and in fruit from highly resistant genotypes may
contribute to the brown rot-resistance of the tissue by interference with
the production of factors involved in the degradation of cutin, rather than
by direct toxicity to the pathogen (Bostock et al., 1999).
The saponin, a-tomatine, present in high concentrations in the peel of
green tomatoes, is inhibitory to B, cinerea and other fungal pathogens,
and its involvement in the development of quiescent infection has been
suggested (Verhoeff and Liem, 1975). In this case, although no further
development of fungal lesions occurred after ripening, tomatine was not
detected in mature fruits (Table 4).
TABLE 4
Tomatine content of tomato fruits*
Fruit tissue
Green fruits (2-3 cm diameter)
Skin of green fruits (2-3 cm in diameter)
Red, ripe fruits
Tomatine content
% of dry
weight
0.5
0.95
none
mg/100 g
fresh weight
43
82
none
* Reproduced from Verhoeff and Liem, 1975 with permission of
Blackwell Wissenschafts-Verlag GmbH.
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