Characterization of Fusarium spp. isolates recovered from bananas (Musa spp.) affected by Fusarium wilt in Puerto Rico

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (FOC), is one of the most destructive diseases of bananas (Musa spp.) worldwide. Although the first report of this disease in Puerto Rico was in 1919, little has been published since that time. We report the first systematic description of FOC on the island. A total of 28 single-spore isolates of Fusarium spp. were recovered from symptomatic bananas from several municipalities. Species identity of the isolates was initially based on morphology and later confirmed with partial sequences of the translation elongation factor 1 alpha (TEF-1 alpha) gene. Isolates were examined for vegetative compatibility, race identity using PCR primers reported for different races, and virulence on tissue-culture-derived plantlets of differential cultivars for races 1, 2 and 4. Most isolates of F. oxysporum belonged to VCG 0124 of FOC, and amplified with primers designed for race 1. Several isolates amplified with primers developed for race 4, but no isolate amplified with primers specific for tropical race 4 (TR4). Most isolates produced symptoms on race 1 or race 2 susceptible cultivars. Although some isolates caused minor symptoms on Gran Nain', disease severities on this race 4 differential were considerably lower than those in susceptible race 1 or race 2 interactions. Based on these results, race 1 and race 2, but not TR4, are present in Puerto Rico. We discuss the disease and FOC's population structure in Puerto Rico, as well as the reliability of different PCR primers that have been developed to identify races of this pathogen.