Direct action of the biocide carbendazim on phenolic metabolism in tobaccoplants

In view of the essential role of phenolic compounds in the development of p athogen resistance iri I plants, and given the influence that fungicides ex ert over phenolic metabolism, the aim of the present study was to determine the effect of the application of different rates of fungicide on the metab olism of phenolic compounds in tobacco plants (Nicotiana tabacum L. cv. Ten nessee 86). The fungicide applied was carbendazim, with a purity of 100%, a t three different rates: 1.3 mM (carb(1)), 2.6 mM (this being the recommend ed concentration, carb(2)), and 5.2 mM (carb(3)). The control treatment was without carbendazim. The results in relation to control plants indicate th at the application of carb(1) in tobacco plants not afflicted by damaging b iotic and abiotic agents boosts phenolic accumulation. Therefore, in the ca se of carbendazim, the application of 50% less (carb(1), 1.3 mM) than the r ecommended dosage (carb(2), 2.6 mM) of this fungicide could be:more effecti ve because the foliar accumulation of phenolics presented at; carb(1) may i mply an increased resistance of plants:to pathogen infection. On the other hand; we found an inhibition of the phenolic oxidation by the application o f carbendazim, principally at carb(3). These results suggest that the exces sive application of carbendazim (5.2 mM:) could be harmful for healthy. pla nts, because, on inhibiting phenolic metabolism (biosynthesis and oxidation ), such treatment would also sharply reduce the capacity of these plants to respond against pathogen attack.