Abstract:
Leaf diseases are an integral part of banana production. While currently not a cause for major concern in South Africa, many of these diseases van reach epidemic proportions and cause severe crop loss. To determine the present status of leaf diseases in South Africa, a survey was conducted in the five banana-growing regions of the country. The study indicated the following: Yello Sigatoka, caused by Mycosphaerella musicola was the most prevalent disease and occurred in all five the regions. Mycosphaerella speckle and Cordana leaf spot, caused by M. musae and Cornana musae respectively, were present in four regions. Cladosporium speckle, caused by Cladosporium musae, was found only in the Levubu area. Various other fungi, mainly saprobes and endophytes, were also isolated. The most commonly encountered species included Alternaria alternate, Colletrichum gloeosporioides, Nigrospora oryzae, N. sacchari, N. Spaerica, Pestalotiopsis sp., Phoma glomerata, Selenophoma asterina and S. juncea. Following morphological identification of the pathogenic species, monoconidial isolates were established from representative isolates of each and their virulence confirmed in artificial inoculation studies. The identity of M. musciola and Cladosporium musae was verified molecularly by means of species-specific primers and/or sequencing of the ITS region. Validation of the identity of Cladosporium musae constitutes the first report of Cladosporium speckle on banana in South Africa. Sequence data of the ITS region of isolates from Mycospaerella speckle lesions indicated that the symptoms are caused by two species, M. musae and one closely related to M. colombiensis, the latter previously described only from lesions on leaves of Eucalyptus urophylla in Colombia.
