Fusarium fujikuroi species complex in brazilian rice

Abstract

Members of the Fusarium fujikuroi species complex (FFSC) are producers of mycotoxins, mainly fumonisins (FBs). In this work, we studied the FFSC species diversity on rice, the presence of essential fumonisin metabolic pathway genes, fumonisin production capacity in vitro and the natural occurrence of mycotoxins in rice. We sequenced 100 isolates for three gene regions (TEF, TUB, CAL). The phylogenetic tree showed that the most frequent species were F. fujikuroi, F. proliferatum and F. verticillioides, then F. anthophilum, F. pseudocircinatum and F. sterilihyphosum. In addition, we found two new phylogenetic lineages, Fusarium sp. 1 and Fusarium sp. 2. All isolates were analyzed for the presence of the FUM1, FUM8 and FUM14 genes and for a the subgroup of 61 isolates the fumonisin production capacity in vitro was assessed. Almost all isolates were gene positive. The species F. fujikuroi, F. proliferatum and F. verticillioides produced fumonisins B1, B2 and B3 in vitro, F. pseudocircinatum, Fusarium sp. 1 and Fusarium sp. 2 produced only FB1, while F. anthophilum and F. sterilihyphosum did not produce any. The natural occurrence of mycotoxins was analyzed in 93 samples subdivided in rice flour and rice hull. All the mycotoxins analyzed were detected, 87% of rice samples were contaminated with at least one of the mycotoxins and 16 % there is no contamination. Among the mycotoxins analyzed, beauvericin was the most prevalent mycotoxin on Brazilian rice grains. This is the first report on the association of several FFSC members with rice grains in Brazil, the ability of these species to produce fumonisins and the natural contamination of rice grains by mycotoxins. Considering the importance of rice in the Brazilian population, our results contribute with new knowledge for the improvement of models for assessing the risk of mycotoxin production on rice in Brazil. Since this study indicates a potential threat to the quality of Brazilian rice. The thesis is divided into three chapters. The first chapter is the review on bakanae, the complex of Fusarium fujikuroi species and mycotoxins. The second chapter on the diversity of FFSC species in rice and the natural occurrence of mycotoxins. And the third chapter on the ability of species present in Brazil to produce fumonisins.