Avaliação dos efeitos da fertilização nitrogenada (uréiae uréia com NBPT) e do Fungicida maxim - XL na produção de fumonisinas por Fusarium verticillioides

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

27/02/2009

RESUMO

Corn is an economically important cereal worldwide, but it is susceptible to toxigenic fungi contamination, mainly Fusarium verticillioides. This fungus produces fumonisins, which cause several mycotoxicoses and probably esophageal cancer in humans. Due to the problems caused by F. verticillioides and fumonisin contamination in corn, during its cultivation some practices can be employed to reduce the crop contamination, such as nitrogen fertilization, since fumonisin biosynthesis is repressed by nitrogen, and fungicide application to control Fusarium verticillioides growth. In this work, natural occurrence of toxigenic fungi and fumonisins was evaluated in freshly harvested corn samples from the Northern Region of Paraná State. The corn kernels were treated with different kinds (urea and urea + urease inhibitor) and doses (80, 160 and 240 Kg/ha) of nitrogen fertilizer. The most frequent fungi genera were Fusarium and Penicillium (83.33% and 98.61%, respectively). Aspergillus sp. was detected in low frequency (4.17%). Fumonisins (B1 and B2) were detected in 100% samples, and high levels of fumonisin (19.49 μg/g) were detected in the treatment without fertilizer application. Although differences in mean fumonisin levels and nitrogen fertilizer doses were not statistically significant, the lowest fumonisin levels (3.13 μg/g) were detected in treatment 2 (160 Kg/ha urea), whereas in the treatments with higher or lower nitrogen doses, fumonisin levels increased. A negative correlation (-0.3780; p<0.05) between nitrogen fertilizer doses and total fumonisin levels was observed. There were no statistically significant differences in mean fumonisin levels and nitrogen fertilizer kind. However, highest fumonisin levels were detected in the treatments where urea + NBPT was applied. The influence of Maxim – XL on the expression of FUM1 and FUM21 genes, and on the fumonisin B1 production by F. verticillioides in defined liquid culture media were also evaluated. Fungicide addition to the culture media increased fumonisin B1 production by 3 – fold (2.31 μg/mL) compared to the control cultures (without fungicide addition). There was no correlation between fumonisin B1 (FB1) and the expression of FUM1, while FUM21 expression was only slightly increased in the presence of fungicide. Taking into account that a strong correlation between fungicide presence, gene expression, and FB1 levels was not observed, some hypothesis are discussed to explain the results. First, Maxim – XL could influence the expression of other genes related to fumonisin biosynthesis. In several fungi, ABC cellular transporters have their expression and/or activity increased in the presence of toxic compounds. FUM19 encodes an ABC transporter, which is responsible for the fumonisin efflux, but it could also be responsible for the fungicide efflux, increasing the extracellular fumonisin levels. Also, the action of the fungicide over MAP kinases could induce alterations in the cell morphology, which, in combination with the agitation used during cultivation, would lead to cellular lyses, increasing the fumonisin concentration in the cell free extract. These results presented ratify the importance of understanding nitrogen fertilization and fungicide mode of action as tools for reducing fumonisin occurrence in corn kernels, and assure food quality for both animals and humans.

ASSUNTO(S)

biotecnologia agrícola milho como alimento uréia como fertilizante fertilizantes nitrogenados agricultural biotechnology corn as food urea as fertilizer nitrogen fertilizers

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