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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
20 Postharvest Diseases of Fruits and Vegetables
2. PENETRATION THROUGH NATURAL INLETS
Some pathogenic fungi and bacteria that cannot normally penetrate
the sound host directly, without the presence of a wound in its surface,
can penetrate through natural openings such as stomata and lenticels.
The penetration of germ tubes of Colletotrichum gloeosporioides spores
into young papaya fruits (Stanghellini and Aragaki, 1966) and the
penetration of Monilinia fructicola spore germ tubes into young stone
fruits (Tate and Corbin, 1978) can take place through the stomata while
the fruit is still in the orchard.
The fungus Dothiorella gregaria (perfect state: Botryosphaeria ribis)
penetrates the lenticels of avocado fruits and forms hyphae that remain
dormant until the harvested fruit has aged (Home and Palmer, 1935).
Penetration through lenticels has also been described for Alternaria
alternata spores in mango and persimmon fruits (Prusky et al., 1981;
Prusky et al., 1983). Penetration through lenticels is typical of
Gloeosporium album and Gloeosporium perennans in apples that grow in
humid areas. In the warm humid season the fungal development in the
lenticels is limited, with their growth being halted until, during storage,
the fruit reaches the required ripening stage (Moreau et al., 1966).
Penicillium expansum, the cause of apple blue mold, and which is
considered a typical "wound pathogen", can also penetrate the fruit
through its lenticels (Baker and Heald, 1934). This phenomenon is most
notable if the lenticels are bruised or when the fruit ages.
The lenticels in potato tubers are liable to develop bacterial soft-rot
during storage. During harvest, most of the lenticels are already infested
with cells of Erwinia cartovora. The bacteria remain inactive within the
lenticels until the development of conditions enhancing the tuber
sensitivity to decay, such as mechanical pressure, the presence of free
water, or a low oxygen pressure within the tuber (Lund and Wyatt, 1972;
Perombelon and Lowe, 1975). Penetration via lenticels is also typical of
Helminthosporium solani, the causal agent of silver scurf of potato tubers
(Burke, 1938), although the fungus can penetrate directly through the
skin of these tubers.
An open calyx tube, typical of some fruits, can also become a natural
penetration point for storage pathogens. This is what enables the
penetration ot Alternaria alternata into Delicious apple fruits (Ceponis et
al., 1969) and Na'ama tomato fruits (Barkai-Golan, unpublished), both of
which are characterized by open calyces. In apple fruits, the fungus that
has penetrated through an open sinus in the calyx region, can develop a
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