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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
322 Postharvest Diseases of Fruits and Vegetables
calyx scar (Dennis 1983b; Fallik et al., 1994b). Incipient infections, which
may appear at the margin of the stem scar, remain quiescent unless the
fruits are subjected to weakening conditions, including chilling injury,
sunscald or over-maturing. The enhancing effects of chilling and of
high-temperature treatments on the susceptibility of tomato fruits to
Alternaria injection has been exhibited at both the mature-green and
mature development stages (Barkai-Golan and Kopeliovitch, 1989).
Prolonged storage can also increase fruit susceptibility. Although the
optimal growth temperature of the fungus is 28°C, it may continue
growing during storage, thanks to the relatively high temperatures
recommended for these cold-sensitive fruits.
A. alternata infections result in firm lesions, slightly sunken and
covered in dense, olive-green to black masses of conidia (McCoUoch et al.,
1982). Pearson and Hall (1975) described incipient infections of
A. alternata on green fruits, which failed to resume activity when the
fruits ripened. This phenomenon resembles the *ghost spotting' described
by Verhoeff (1974) in green tomatoes infected by JB. cinerea.
The development of A. alternata in tomatoes may be associated with
the production of several non-specific toxic metabolites in the infected
fruits. Stinson et al. (1981) found that the main toxin in infected tomato
fruits was tenuazonic acid; others, such as alternariol, alternariol
monomethyl ether and altenuen were found in much smaller amounts.
However, working with another strain of A, alternata, Ozcelik et al.
(1990) reported that the major toxin in infected tomatoes was alternariol,
followed by alternariol methyl ether. Fungal growth, along with toxin
production, occurred at temperatures between 4 and 25°C.
C. Erwinia carotovora ssp. carotovora (Jones) Dye and Erwinia
carotovora ssp. atroseptica (van Hall) Dye
These soft rot bacteria are among the most common postharvest
pathogens of tomatoes and peppers, and are found in the soil and plant
debris wherever they are grown. These pathogens are spread by
splashing of contaminated soil, by wind, by insects and by postharvest
washing (Bartz, 1982). They are wound pathogens, requiring moisture to
initiate infection, and entering the fruit under warm, wet conditions,
through breaks in the skin, the cut stem or any injury incurred during
picking and packing (Volcani and Barkai-Golan, 1961; Sherman et al.,
1982). Growth and multiplication of the bacteria are favored by wet
conditions and temperatures of 24-30°C. Under these conditions, the
entire fruit may rot in a few days.
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