Cercospora leaf spot af bananas

Sigatoka leaf spot disease (SD) is a disease of bananas and is caused by the ascomycetous fungus, Mycosphaerella musicola. This pathogen can be distinguished morphologically from Mycosphaerella fijiensis, which causes black leaf streak disease (BLSD), by the characteristics of the conidia and conidiophore. The anamorph of M. musicola, Pseudocercospora musae, lacks the thickened cell walls that are present at the base of the conidia of Paracercospora fijien, the anamorph of M. fijiensis, and are shorter and less wavy. The conidiophores of P. musae are bottle-shaped and much smaller than the elongated conidiophores of P. fijiensis which are often bent and bear conspicuous conidial scars. The two species can also be differentiated by molecular methods.

It is not always easy to differentiate between the symptoms of SD and BLSD. The first sign of disease in SD is the appearance of small yellow streaks on the upper side of leaves while in BLSD small, dark brown streaks appear on the lower surface of leaves. These streaks enlarge and coalesce forming necrotic lesions with light gray centres and yellow perimeters. Large areas of leaf can be damaged causing a lowering of photosynthetic ability, a reduction in crop yield and premature ripening of the fruit. BLSD is the more serious of the diseases as the symptoms emerge on younger leaves and it affects many cultivars that have developed resistance to SD, including the plantain subgroup.