Postharvest Fruit Rot of Tomato in Brazil Caused by Fusarium boothii

Tomato (Solanum lycopersicum L.) is common in the daily diet of Brazilians and is an important income source for those who grow and market the fruit. In July 2012, while monitoring fungi associated with fruit and vegetable postharvest decay at a wholesale produce distribution center (Ceasa Minas) in the state of Minas Gerais, tomato fruits (cv. Carmem) with a postharvest decay were observed. The symptomatic fruits were detected sporadically and appeared to have caused minimal losses. Sunken, brown lesions with abundant sporodochia were observed on fruit stored at 25°C. Inside the fruit, profuse white mycelium with a purplish pigment was observed. The fungus was examined with a stereomicroscope, and pure cultures were obtained by transfer of single spores to potato dextrose agar (PDA) containing 4 μg of rifamycin per liter. An isolate was deposited in the culture collection of the Universidade Federal de Viçosa (Accession COAD 1778). Abundant aerial mycelium and a reddish pigment developed on PDA after 7 days at 25°C. On synthetic nutrient-poor agar, macroconidia were observed, usually with 5 septa per conidium, with the dorsal and ventral surfaces often parallel and gradually curved, and spores 30 to 45 × 2.75 to 4.5 μm. Microconidia were absent. On the basis of these morphological characteristics, the fungus was identified as belonging to the Fusarium graminearum species complex. To determine the species in the F. graminearum complex, TEF-1α gene amplification with the PCR primers EF1T and EF2T was carried out using DNA extracted from an isolate (2). Submission of the 644-bp sequence to GenBank (Accession No. KM437633) revealed 99.22% similarity to the TEF-1α sequence of F. boothii O’Donnell, T. Aoki, Kistler & Geiser strain FD 01128 in Fusarium-ID, a database of DNA sequences for the genus Fusarium designed to assist in the identification of species (1). When checked against the Fusarium Multi Locus Sequence Typing database, the sequence was 99.39% similar to the TEF-1α sequence of F. boothii strain CBS 316.73, thus confirming identification of the species as F. boothii. Pathogenicity tests were performed by inoculating tomato fruit (cv. Carmem) with 6-mm-diameter PDA plugs colonized by the isolate of F. boothii. Five wounded fruits were inoculated with colonized agar plugs, and five fruits each treated similarly with a sterilized PDA plug served as a noninoculated control treatment. The fruits were kept in plastic boxes containing moistened cotton. The boxes were covered with Parafilm and incubated at room temperature. After 7 days, all inoculated fruits developed the same symptoms observed on the original fruits from the market, and the same fungus was reisolated from the fruit to fulfill Koch’s postulates. All control fruits remained asymptomatic. To our knowledge, this is first report of F. boothii causing postharvest rot of tomato fruit. In addition, there are implications for human health due to toxin production by the fungus (3) and the potential for consumption of infected fruit.