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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Host Protection and Defense Mechanisms 79
resistance to decay (Afek et al., 1995c). This supposition is derived from
the following facts: (a) columbianetin exhibits stronger activity than
psoralens against Alternaria alternata, B, cinerea and S, sclerotiorum,
the main postharvest pathogens of celery; (b) the concentration of
psoralens in celery is much lower than that required to inhibit the
growth of celery pathogens, while the concentration of columbianetin in
the tissue is close to that required for their suppression; (c) increased
sensitivity of celery to pathogens during storage occurred in parallel with
the decrease in the concentration of columbianetin, and with the increase
in that of psoralen (Fig. 12).
The phytoalexin capsidiol is a sesquiterpenoid compound produced by
pepper fruits in response to infection with a range of fungi (Stoessl et
al., 1972). Pepper fruits inoculated with B. cinerea and Phytophthora
capsici contain only small quantities of capsidiol, whereas fruits
inoculated with saprophytic species or with weak pathogens may
produce higher concentrations of the phytoalexin, which inhibit spore
germination and mycelial growth. Inoculating peppers with Fusarium
c
o
CO
c
0
o
c
o
o
80
60 +
40
20 +
0
Coiumbianetin
Furanocoumarins
1 2
Time (weeks)
Fig. 12. Concentration of columbianetin and total furanocoumarins in celery
during 4 weeks of storage at 2°C. Vertical bars indicate standard error.
(Reproduced from Afek et al., 1995 with permission of Elsevier Science).
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