Abstract
A description is provided for Mycosphaerella fijiensis. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Musa spp. DISEASE: Black leaf streak of banana. A comparison of the conidial states of M. fijiensis and M. musicola (CMI Descript. 414, Sigatoka of banana) has been given, as has a detailed account of the symptoms (48, 3071; and see 44, 191, 1180; 45, 1867). Initially reddish-brown specks form on the lower leaf surface, they elongate to become streaks up to 20 × 2 mm, with the long axis parallel to the leaf veins and at this stage are more clearly visible on the lower leaf surface. The streaks can be extremely numerous; they darken, become almost black and are clearly seen on the lower surface. The streak develops into a fusiform or elliptical spot, with a light brown, water soaked margin and a dark centre. The centre dries out becoming light grey or buff, sunken, surrounded by a narrow dark brown or black border and often by a chlorotic zone beyond. Necrosis of the whole leaf can occur in 3-4 weeks. Some differences in the macroscopic leaf symptoms between black leaf streak and Sigatoka occur. In the latter disease the early stage streaks are clearly seen on the upper surface and are yellowish; in the former the streaks are darker at similar stages in development. But there are no clear macroscopic differences between the mature spots of the two diseases. GEOGRAPHICAL DISTRIBUTION: The disease was first described from Fiji in 1963 (although because of probable confusion with M. musicola there may be earlier unsubstantiated records). It is widespread in the islands of the Pacific (Oceania); it may be absent from the mainland of S.E. Asia and does not occur in Australia, Africa or America (CMI Map 500, ed. 1, 1974). TRANSMISSION: Perithecia are formed in abundance and, therefore, the ascospores are considered important in spread, perhaps more so than the conidia (44, 1180; 45, 1867). In dry weather ascospore concentration reached a max. near 0600 h as dew formed. On rainy days peak concentrations were reached shortly after rain began. Seasonal increases in ascospores were associated with those of rainfall and relative humidity (52, 4160).