Fusarium fujikuroi species complex in Brazilian rice: Unveiling increased phylogenetic diversity and toxigenic potential.

Fusarium fujikuroi species complex (FFSC) species are commonly encountered infecting rice, but knowledge of the diversity and toxigenic potential of the species is lacking in Brazil, the largest rice-producing country outside Asia. One hundred FFSC isolates obtained from national rice were identified using morphology and phylogeny of TEF, CAL and TUB genes. Eight previously known and one novel Fusarium species were identified. Three species accounted for around 60% of the strains: F. fujikuroi (n = 23), F. proliferatum (n = 22) and F. verticillioides (n = 16). The less frequent species were F. volatile (n = 8), F. anthophilum (n = 6), F. pseudocircinatum (n = 4), F. sterilihyphosum (n = 2) and F. begoniae (n = 1). The novel Fusarium species was represented by 18 isolates. All species produced at least one of the analyzed mycotoxins [beauvericin (BEA), fumonisins (FBs), moniliformin (MON) and enniatins (ENNs)]. BEA was produced by all species but F. verticillioides. The FBs (mainly FB1) were produced mostly by F. fujikuroi, F. proliferatum and F. verticillioides. F. begoniae and F. verticillioides did not produce ENNs and F. sterilihyphosum and F. begoniae did not produce MON, while the other species produced MON and ENNs. Our results add new knowledge of the diversity, geographical distribution and host range of FFSC species.

Fusarium incarnatum-equiseti species complex associated with Brazilian rice: Phylogeny, morphology and toxigenic potential.

Fusarium incarnatum-equiseti species complex (FIESC) is commonly detected in Brazilian rice, but knowledge of the species limits and their toxigenic potential is lacking. Seventy strains morphologically identified as FIESC-like, isolated from the major rice-growing regions of Brazil, were subjected to sequencing of EF-1α gene. Among them, 18 strains were selected and analyzed for their RPB2 gene sequences. Nine phylogenetic species were identified, among which eight matched the previously reported FIESC 4 (F. lacertarum), 6, 16, 17 (F. pernambucanum), 20 (F. caatingaense), 24, 26 and 29. One new phylogenetic species was identified, and named FIESC 38. Five strains formed new singleton lineages. The most dominant species were FIESC 26 (22/70 strains) and FIESC 38 (21/70), the newly identified species. The incarnatum morphotype was dominant (10 phylogenetic species) over the equiseti (4 species). Among 46 strains selected to represent all species, only 16 strains produced detectable levels of mycotoxins in vitro. FIESC 26 produced ZEA and FIESC 38 produced both ZEA and DON. ZEA was produced by nine isolates of three other species, among which few isolates produced trichothecenes: DON (5/46), NIV (3/46), 4-ANIV (2/46), 15-ADON (1/46) and 3-ADON (1/46). The T-2 and HT-2 mycotoxins were not detected. Our results contribute novel information on species limits and mycotoxin production within cereal-infecting FIESC in the southern hemisphere and provide baseline data for further exploring morphological differences among the species.

Regional and field-specific factors affect the composition of fusarium head blight pathogens in subtropical no-till wheat agroecosystem of Brazil.

A multiyear survey of >200 wheat fields in Paraná (PR) and Rio Grande do Sul (RS) states was conducted to assess the extent and distribution of Fusarium graminearum species complex (FGSC) diversity in the southern Brazilian wheat agroecosystem. Five species and three trichothecene genotypes were found among 671 FGSC isolates from Fusarium head blight (FHB)-infected wheat heads: F. graminearum (83%) of the 15-acetyldeoxynivalenol (15-ADON) genotype, F. meridionale (12.8%) and F. asiaticum (0.4%) of the nivalenol (NIV) genotype, and F. cortaderiae (2.5%) and F. austroamericanum (0.9%) with either the NIV or the 3-ADON genotype. Regional differences in FGSC composition were observed, with F. meridionale and the NIV type being significantly (P<0.001) more prevalent in PR (>28%) than in RS (≤9%). Within RS, F. graminearum was overrepresented in fields below 600 m in elevation and in fields with higher levels of FHB incidence (P<0.05). Species composition was not significantly influenced by previous crop or the stage of grain development at sampling. Habitat-specific differences in FGSC composition were evaluated in three fields by characterizing a total of 189 isolates collected from corn stubble, air above the wheat canopy, and symptomatic wheat kernels. Significant differences in FGSC composition were observed among these habitats (P<0.001). Most strikingly, F. meridionale and F. cortaderiae of the NIV genotype accounted for the vast majority (>96%) of isolates from corn stubble, whereas F. graminearum with the 15-ADON genotype was dominant (>84%) among isolates from diseased wheat kernels. Potential differences in pathogenic fitness on wheat were also suggested by a greenhouse competitiveness assay in which F. graminearum was recovered at much higher frequency (>90%) than F. meridionale from four wheat varieties inoculated with an equal mixture of F. graminearum and F. meridionale isolates. Taken together, the data presented here suggest that FGSC composition and, consequently, the trichothecene contamination in wheat grown in southern Brazil is influenced by host adaptation and pathogenic fitness. Evidence that F. meridionale and F. cortaderiae with the NIV genotype are regionally significant contributors to FHB may have significant implications for food safety and the economics of cereal production.