First Report of Black Sigatoka of Banana Caused by Mycosphaerella fijiensis in Bahia, Brazil

Black sigatoka, caused by the fungus Mycosphaerella fijiensis Morelet (anamorph Pseudocercospora fijiensis [Morelet] Deighton), is a major economic threat to the mostly highly susceptible banana cultivation worldwide (Churchill 2011). In Brazil, it was reported for the first time in 1998, in the State of Amazonas, in plantations located in the municipalities of Benjamin Constant and Tabatinga, bordering Colombia and Peru (Trindade et al. 2002). The northeast region of the country was considered free of black sigatoka. An intensive survey was conducted by the Agricultural Defense Agency of Bahia to detect the presence of M. fijiensis. In September 2015, the typical symptoms of black sigatoka were observed in the municipality of Cruz das Almas (12°39′26.9″S, 39°04′55.71″W). As occurred with yellow sigatoka, black sigatoka is also widespread in all regions of Brazil after it was recently found in Bahia. The first symptoms appeared as light brown striations approximately 2 to 4 mm in length in the surface of the abaxial leaf. As the disease progresses, the striations expand radially and longitudinally, reaching up to 3 cm in length, and they can be seen on the adaxial surface of the leaf with dark brown color. In more advanced stages, the striations turn into irregular spots that coalesce, giving the leaf a color close to black (Meredith and Lawrence 1969). Thirty isolates were obtained by cultivation on potato dextrose agar medium at 25°C and a 12-h photoperiod. The conidia were hyaline to pale olive, straight or slightly curved, 58.5 to 71.5 × 3.4 to 4.5 µm, with one to eight septa, thin at their apex and wider at the base, with a scar at the base. The conidiophores were dark, straight or slightly geniculate, 38.7 to 58.4 × 3.8 to 4.9 µm, isolated or in small groups without stroma, with a thickened wall on the conidian scars. Pathogenicity was evaluated in 90-day-old banana plants of the cultivars Prata Anã (group AAB) and Grande Naine (group AAA), both susceptible to black sigatoka under greenhouse conditions. A spore suspension with 1 × 10⁴ conidia/ml was atomized on the underside (abaxial surface) of the first and second leaves of each plant. Six plants per cultivar were inoculated with each of the 14 isolates evaluated. The inoculated leaves were kept in a moist chamber for 48-h. After 15 days, typical symptoms were observed in all inoculated plants. The total fungal DNA was extracted from 30 isolates by the cetyltrimethylammonium bromide protocol (Murray and Thompson 1980), and internal transcribed spacer (ITS) sequences were obtained using ITS1 and ITS4 primers (Glass and Donaldson 1995). The sequences obtained (GenBank nos. MG679477 to MG679499) were 96 to 100% similar to M. fijiensis sequences from GenBank. Bahia’s banana production is characterized for being domestic, with 93% destined to the 27 states and 7% to its own market, with 80% of small producers and a production area of 85,000 ha distributed throughout the country. The main varieties produced are Prata, Terra (platano), Grande Naine (Cavendish), and Apple (Silk), all susceptible to black sigatoka. Black sigatoka is an important disease of banana and a quarantine pest in some regions of the Brazil. To our knowledge, this is the first report of M. fijiensis in Bahia state, where it can threaten a production that reached 1.1 million tons in 2017 and employed approximately 170,000 workers.