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Disease Cycle and Epidemiology

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Epidemiology

With black Sigatoka, ascospores, and to a certain extent conidia, are the propagules by which the fungus is dispersed.

Conidia form readily in high humidity, especially if a film of free water is present on leaves. These asexual spores disperse during rain-wash and splashing, causing local spread of the disease.

Pseudothecia mature when dead leaf tissues are saturated with water for approximately 48 hours. Ascospores are the primary means of long distance dispersal and are the main means of spreading during extended periods of wet weather. Mycosphaerella fijiensis forms relatively few conidia, so ascospores are thought to be more important in the disease cycle.

Sigatoka leaf spot on bananas decreases somewhat during the dry season but otherwise produces more or less continuously repeated cycles of infection (Figure 15).

Figure 15