Especies de Fusarium associadas ao sorgo no Brasil: diversidade, patogenicidade e potencial toxigênico

Abstract

Species of the Fusarium fujikuroi species complex (FFSC) can be found in association with sorghum, millet and corn as endophytes, pathogens or mycotoxin producers. The aim of this study was to evaluate the diversity of species in the FFSC which occur in association with sorghum in Brazil and to evaluate the toxigenic and pathogenic potential. Inchapter 1, a literature review was conducted regarding sorghum, the diseases caused by species of the FFSC and mycotoxin production. In chapter 2, isolates from sorghum grains from different regions of Brazil were evaluated by phylogenetic analysis of the gene region elongation factor 1- α region (Tef-1 α ), sexual compatibility tests, morphological markers, in vitroproduction of mycotoxins fumonisin B1, B2 and moniliformin, and pathogenicity tests in sorghum, millet and corn stalks. The phylogenetic analysis of the Tef-1αgene showed the presence of F. andiyazi, F. proliferatum, F. thapsinum and F. verticillioides. The morphological markers confirmed the identity of the isolates. Among the isolates of F. proliferatum and F. thapsinum, the production of high levels of FB1 and moniliformin was observed, while the production of FB2 occurred only occasionally. F. verticillioides isolates produced higher levels of FB1and FB2 and differentiated themselves from F. proliferatum and F. thapsinum through the production of low levels of moniliformin. A high variation in theamount of mycotoxins was observed among F. andiyazi isolates. Half of the isolates produced fumonisin and moniliformin at low and high levels, while the other half did not produce toxins. The phylogeny indicates diversity within F. andiyazi, suggesting that more than one population or species may be present in Brazil. Isolates selected from the four species induced stem rot symptoms in sorghum, maize and millet cultivars. F. thapsinumand F. andiyaziwere more aggressive to sorghum, while F. verticillioidesand F. proliferatumwere more aggressive to corn. In chapter 3, a field study was conducted to evaluate the ability of the four species of Fusarium to colonize sorghum grains and produce fumonisin. The damage caused by these species to grain yield and seed germination was also assessed. Panicles of three sorghum cultivars were inoculated with isolates of the four species in the off-season period (2015) and in the harvest period (2015/2016). Analyses of the incidence of Fusariumin the grains, a seed germination test, an evaluation of productivity and the detection of fumonisin were performed. The three analyzed sorghum cultivars were susceptible to colonization by Fusarium species, and the BRS 308 showed a higher average of incidence. The isolates were able to produce fumonisins in different concentrations, and F. proliferatum produced higher levels of fumonisins in all cultivars analyzed. The productivity of the plants and the germination of seeds were also affected. Chapter 4 presents more results obtained on F. andiyazithat were not included in chapters 2 and 3 and will be used in the preparation of another publication. It was concluded that the species of Fusariumcan affect sorghum production in Brazil. Therefore, the incidence of these species should be carefully monitored for quality assurance and for the safety of the sorghum produced in the country.