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

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Postharvest Disease Summary 287
fungal growth and complete penetration of the fruit peel occur only after
the onset of ripening (Prusky and Keen, 1993). Infected avocados may
thus be harvested without any visible symptoms and the disease
develops later during storage or marketing. Typical symptoms of
anthracnose, which appear only when the fruit begins to soften, include
circular dark spots and, later, sunken lesions which, under humid
conditions, give rise to masses of salmon-pink conidia.
2. Dothiorella gregaria Sacc. (perfect state: Botryosphaeria ribis
Grossenb. & Duggar)
Dothiorella may exhibit both the asexual state (pycnidia with conidia)
and the sexual state (perithecia and ascospores) on dead twigs and
leaves. Under wet conditions spores may infect the fruits on the tree, via
their stomata and lenticels, and the infection then remains quiescent.
Progressive lesions generally develop when the fruit begins to soften
after harvest (Labuschagne and Rowell, 1983). The same fungus, alone or
in association with other fungi, is also responsible for stem-end rot
(Muirhead et al., 1982).
3. Stem-End Fungi
The stem-end fungi are found on dead branches and bark of avocado
trees. Botryodiplodia theobromae Pat. [perfect state: Physalospora
rhodina (Berk. & Curt.) Cooke], is typically a wound pathogen and
avocado infections frequently take place during harvest. The decay
originates at the stem end and proceeds, rather uniformly, towards the
blossom end. It may infect the pedicel during fruit development but,
since avocados do not ripen on the tree, the infection remains quiescent
until after harvest, when the fruit ripens. Dothiorella gregaria and
Phomopsis spp., however, are capable of causing latent infections in
developing fruits (Peterson, 1978). Generally, stem-end rots caused by
Alternaria alternata are less common. However, after prolonged
commercial use of the systemic fungicide, thiabendazole to treat
avocados, Alternaria alternata, which is insensitive to this fungicide, has
become a major cause of stem-end rot in stored fruits (Zauberman et al.,
1975).
Control Measures
Anthracnose development may be reduced by preventing injuries to
the fruit, in the orchard or during harvesting and handling (Smoot et al.,
1983). The disease is particularly important during prolonged storage.
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