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

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Postharvest Disease Summary 271
2. Stem-End Pathogens
The principal stem-end rot pathogens of citrus fruits are:
(i) Diplodia natalensis P.E., frequently referred to as
Botryodiplodia theobromae Pat. [(perfect state: Physalospora
rhodina Berk. & Curt.) Cooke];
(ii) Phomopsis citri Fawcett (perfect state: Diaporthe citri Wolf);
(Hi) Dothiorella gregaria Sacc. (perfect state: Botryosphaeria
ribis Grossenb. & Duggar).
(Hi) Alternaria citri Ell. & Pierce, which was renamed A alternata
(Fr.) Keissler pv. citri (Solel, 1991).
Stem-end rots caused by D, natalensis and P. citri are the major
postharvest diseases in citrus fruits grown in humid subtropical areas
with high rainfall during the growing season. These fungi, as well as
D. gregaria, may assume the sexual state, namely perithecia, which give
rise to ascospores. However, this form is not commonly found and the
asexual spores, borne within pycnidia, are the only spores important for
infection. The pycnidia are produced in dead wood and in living tissues of
stems and leaves.
Infection may be initiated at any stage of fruit development, when
wind and splashes of rain carry the pathogen spores to the surface of
immature fruits on the tree. However, immature fruits are resistant to
invasion, and the fungi remain quiescent in floral remnants under the
sepals of the fruit and do not become active until the buttons become
senescent and begin to separate from the fruit (Brown, G.E. and Wilson,
1968). Diplodia usually progresses rapidly down the central axis,
frequently reaching the stylar-end; it grows along the tissues that divide
the fruit into segments of the pulp, taking on the appearance of fingers
that connect the rotted ends of the fruit (Smoot et al., 1983). Similar
symptoms can arise from Dothiorella development. Phomopsis decay is
characterized by some shriveling of the decayed tissue, and this helps to
separate the decayed from the sound tissue. The fungus similarly
progresses down the core but does not reach the stylar end until most of
the rind has decayed. Infection by the three fungal species may, however,
originate at injuries on the side or at the stylar end of the fruit.
Stem-end rots caused by Diplodia, Phomopsis and Dothiorella may
occur in the same lots or even on the same fruit, and it is often difficult or
impossible to distinguish among them. When Diplodia and Phomopsis
develop on the same fruit, an important factor in determining which will
predominate is the temperature (Smoot et al., 1983): the optimum
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