Black Sigatoka, also known as black leaf streak, is caused by Mycosphaerella fijiensis Morelet (anamorph Pseudocercospora fijiensis (Morelet) Deighton). It is the most significant disease of bananas and plantains (Musa spp.) because most of the economically important cultivars of exported and staple commodities are highly susceptible. The Caribbean is one of the few regions of the world where black Sigatoka is not widespread. Black Sigatoka has been reported in the Bahamas, Cuba, Hispaniola, and Jamaica (2). Yellow Sigatoka, caused by M. musicola Leach (anamorph P. musae (Zimm.) Deighton), has been recognized in Puerto Rico since 1938-1939 (3). In August 2004, symptoms resembling black Sigatoka were first observed in Añasco, Puerto Rico by extension personnel from the University of Puerto Rico. Since black and yellow Sigatoka produce similar disease symptoms, a survey was conducted in the western banana- and plantain-production region of Puerto Rico to confirm the presence of black Sigatoka. Leaf samples were collected from production fields near the towns of Las Marias, Maricao, and Añasco. Single-ascospore isolates were recovered using the discharge technique from moistened pseudothecia in necrotic lesions that were inverted over water agar, and ascospores were transferred to potato dextrose agar. The isolates were subcultured in potato dextrose broth for mycelium production. DNA was isolated from mycelium with the FastDNA kit (Q-Biogen, Irvine, CA) for 19 isolates. Internal transcribed spacer as well as the 5.8s rDNA regions were polymerase chain reaction amplified with primers specific to M. fijiensis or M. musicola (1). Amplification products (˜1,100 bp) were observed for 18 of the 19 isolates, 6 of which were M. fijiensis and the remaining 12 were M. musicola, while the positive controls for both species were also amplified with the respective primer pairs. M. fijiensis was recovered from production fields close to all three towns. The source of M. fijiensis in Puerto Rico is unclear, but it may have originated from introduced leaf material and/or wind dispersed ascospores from neighboring countries. The presence of black Sigatoka in Puerto Rico will most likely increase production costs where fungicide applications will be needed to maintain yields. The USDA-ARS, Tropical Agriculture Research Station is the official Musa spp. germplasm repository for the National Plant Germplasm System. As such, efforts are underway to introduce and evaluate black Sigatoka disease-resistant clones that can satisfy local and export market criteria.
References: (1) A. Johnasen. Detection of Sigatoka leaf spot pathogens of banana by the polymerase chain reaction. Chatman, UK, Natural Resource Institute, 1997. (2) R. C. Ploetz. Plant Dis. 88:772, 2004. (3) R. H. Stover. Trop. Agric. Trinidad. 39:327, 1962.
