ABSTRACT: Mycotoxin levels in Fusarium head blight (FHB) infections can be difficult to quantify. The relationship between mycotoxin and disease is not consistent and it is not clear if wheatpathogen interaction is of significance in regions where more than one Fusarium species with distinct trichothecene production ability co-exists. This study aimed to investigate whether a set of eight Brazilian wheat genotypes, varying in resistance according to classification by the breeder, exhibit a common or differential resistance to Fusarium graminearum (Fgra) (deoxynivalenolproducing) and Fusarium meridionale (nivalenol-producing) (Fmer) using full-spike and central spikelet inoculation (type II resistance). Fgra was generally more aggressive than Fmer based on the percentage of diseased spikes (99 and 84 %, respectively) and number of diseased spikelets (mean 2.8 and 2.0, respectively) below the central spikelet. The genotype-pathogen species interaction was not significant, but there were differences between the genotypes, with BRS 194 and BRS 327 being the least and most resistant, respectively, based on severity ratings. The incidence of Fusarium-damaged kernel (FDK, %) was not affected by species, but two genotypes (BRS Parrudo and BRS 327) showed a lower incidence of FDK. There were substantial variations in the accumulation of deoxynivalenol and nivalenol among the genotypes, reaching maxima of 691.2 µg g−1 and 355.2 µg g−1, respectively, suggesting that Fgra is a more potent producer of trichothecene. Our data confirm prior resistance classifications by the breeders and suggest that the use of a single highly aggressive Fgra isolate may be sufficient for effective screening for FHB resistance. However, further studies are needed to elucidate the accumulation of resistance to trichothecene.

Embora Fumonisina B1 (FB1) seja uma micotoxina pouco estudada em trigo, os fungos do gênero Fusarium são frequentemente detectados neste cereal, principalmente em regiões subtropicais, como o Sul do Brasil, o que justifica a necessidade de avaliar sua ocorrência. Neste estudo, foram avaliadas a micobiota, atividade de água e a presença de FB1 em 11 cultivares de trigo cultivados nas regiões nordeste e noroeste do Rio Grande do Sul. A micobiota foi identificada por técnicas morfológicas e moleculares e a FB1 foi determinada por cromatografia líquida e detecção por fluorescência (HPLC-FL). Nas amostras analisadas, foi verificada uma contagem inferior a 103UFC, e os fungos dos gêneros Phoma, Cladosporium e Fusarium foram os mais frequentes. Apesar disso, 54% das amostras estavam contaminadas com FB1 em níveis variando de 958 a 4906µg de FB1 kg-1.

Although fumonisin B1 (FB1) is a mycotoxin poorly studied in wheat, the Fusarium genus fungi have been frequently detected in this cereal, especially in subtropical regions such as southern Brazil, thus studies on their occurrence are required. This study evaluated the mycobiota, water activity and the presence of FB1 in 11 wheat cultivars grown in the northeastern and northwestern of Rio Grande do Sul. The mycobiota was identified by morphological and molecular techniques and FB1 was determined by liquid chromatography with fluorescence detection (HPLC-FL). Microbial counts lower than 103CFU were found in the samples, and the fungi genera Phoma, Cladosporium and Fusarium were the most frequent. Despite this, 54% of the samples were contaminated with FB1 at levels ranging from 958 to 4,906µg FB1 kg-1.