Mycosphaerella fijiensis also known as black sigatoka, is an ascomycete fungus that causes leaf-spot of banana.
Life cycle and appearance of Black sigatoka disease
Black sigatoka (Mycosphaerella fijiensis) produces both ascospores and conidia. The ascospores are wind-dispersed over longer distances, the conidia are splash-dispersed within the crop. Both types of spores cause the exact same symptoms. They enter the leaf through the stomata. After infection, hyphae emerge from the stomata and either develop into conidiophores with new conidia or grow across the surface and infect adjacent stomata. Both types of spores can germinate within two or three hours under humid conditions, but infection takes a minimum of two or three days under optimal conditions (humidity close to saturation and temperature above 20 °C).
Black sigatoka (Mycosphaerella fijiensis) first causes small, light yellow spots or streaks on leaves of about one month old. The symptoms run parallel to the veins. Within a few days, the spots become a few centimetres in size and turn brown with light grey centres. These spots enlarge further and the tissue around the lesions turns yellow and dies. Lesions merge and the whole leaf turns brown and ultimately dies. In cases of severe infection leaves may die within a few weeks. Because of the lack of leaf tissues, fruit maturity is hampered.