Espécies de Fusarium associadas a Cucurbitáceas no Brasil

Abstract

In this study we investigate which species of the Fusarium solani species complex (FSSC) are associated with cucurbits in Brazil and which of them cause stem rot, root rot, and rot of fruits. We still report the occurrence of species of the Fusarium chlamydosporum species complex (FCSC) and Fusarium incarnatum-equiseti species complex (FIESC), causing fruit rot on pumpkins. A collection of 72 isolates (FSSC = 67, FCSC = 3, FIESC = 2) was obtained in the states of MG, RN, CE, PI, GO, PE, RR, and MA. Isolates were grouped into morphotypes, according to their morphological markers. Monospore isolates of FSSC and FCSC were identified by molecular phylogeny using partial sequences of the EF-1α + RPB2 genes, while for isolates of the FIESC, EF-1α + LSU + RPB2 + CAM sequences were used. The mating type idiomorphs were identified for isolates of the FSSC by a PCR reaction, for the application of the biological species concept using lab crossings. Representative isolates were selected for pathogenicity tests in pumpkin plants and fruits, and to evaluate transmission from seeds to plants. According to the molecular phylogenetic analysis using maximum parsimony, strains of FSSC belong to six different species: F. petroliphilum (FSSC 1), F. keratoplasticum (FSSC 2), F. falciforme (FSSC 3+4), F. solani f. sp. cucurbitae(FSSC 10) and “Neocosmosporasuttoniana” (FSSC 20), representing heterothallic species, and F. pseudensiforme (FSSC 33), an homothallic species. Strains of FCSC represent two phylogenetic species, FCSC 1 (n=2) and FCSC 2 (n=1). Strains of FIESC were identified as F. lacertarum and FIESC 39, a so far unknown phylogenetic species within this complex. “Neocosmosporasuttoniana” formed fertile perithecia when strains of opposite mating types were crossed in the lab. The sexual stage of this species had not been reported before in the literature. All evaluated species caused disease when inoculated in pumpkin plantlets. Fusarium cucurbitae was the most virulent, causing death of plants 5 to 10 days after emergence. Species of FCSC and FIESC caused yellowing symptoms, and reduction of plant height and the root system of pumpkin plants. On fruits, major lesions were caused by F. cucurbitae and “N. suttoniana”. Transmission from seeds to plants was confirmed for all species. Fusarium cucurbitae is the most virulent species, reducing germination rate in 82% and 35% of seed vigor. Fusarium keratoplasticum,and F. pseudensiforme are reported here for the first time in association with cucurbits. Fusarium petroliphilum, F. keratoplasticum, F. cucurbitae, and F. pseudensiforme had not been reported before in association with cucurbits in Brazil. Fusarium lacertarum and the phylogenetic lineages FIESC 39 and FCSC 2 are also reported for the first time causing fruit rot of pumpkins. Fusarium solani f. sp. cucurbitae (FSSC 10) is now known as Fusarium cucurbitae. This study contributes to the knowledge about species diversity associated with cucurbits in production areas in Brazil. It will also support the development of plant disease management strategies and the search for genetic resistance in cucurbit germplasm.