Leveduras: controle biológico de antracnose em soja e sensibilidade à fungicidas

Abstract

In view of the excessive use of chemical products that have led to contamination and reports of inefficiency of active principles, effective alternative methods for the management of anthracnose (Colletotrichum truncatum) in soybean cultivation are necessary. Therefore, the objective was to evaluate the potential of yeasts in the biological control of anthracnose in soybean, evaluating the reduction in disease severity and the effect on the activity of proteins related to plant defense, in addition to evaluating the sensitivity of the strains when subjected to contact with fungicidal products. An in vivo test was carried out in a greenhouse to evaluate the potential of 35 yeast strain to reduce the severity of anthracnose in soybean plants, by evaluating the percentage of injured leaf area. Eight strains efficient in reducing the disease were selected for a new assay, where the activity of enzymes related to plant defense was evaluated. To determine the defense enzymes, soybean plants were treated with yeast strains and later inoculated with the pathogen C. truncatum. Finally, an in vitro test was carried out to evaluate the sensitivity of 37 yeast strains to fungicidal products. For this, the size of the inhibition halo of yeasts when in contact with five fungicide products and two agricultural sprays was evaluated. It was found that 85% of the yeast strains, being all Rhodotorula spp., Pichia spp., Zygoascus hellenicus and Sporidiobolus johnsonii strains and 50% of the Cryptococcus laurentii and Candida albicans strains, reduced the severity of anthracnose in soybean. On the other hand, none of the selected yeasts induced an increase in protein content and did not promote increases in phenylalanine ammonia-lyase activity. The strain R. aurantiaca (AH 12-3) showed a priming effect increasing the peroxidase activity after inoculation of the pathogen. The strain Z. hellenicus (AH 06-2) induced β-1,3-glucanase activity with the treatment, but inhibited the peroxidase activity with the arrival of the pathogen. It was observed that the yeasts Z. hellenicus, R. aurantiaca, Pichia spp. and Sporobolomyces roseus were insensitive to most of the tested fungicides, while the yeast C. laurentii was inhibited to some degree by all products, with the exception of Bordeaux mixture. Regarding the products, those composed of a mixture of strobilurins and carboxamides, acting on only one mechanism of action, the inhibition of respiration and the multisite products proved to be less toxic to yeasts, while the products containing the active ingredient of the triazole group, acting on the inhibition of sterol synthesis in membranes, showed greater toxicity. The results indicate that yeasts have the potential to reduce the disease, but that each isolate can contribute differently in the induction of resistance. The tested yeasts present insensitivity to most of the tested fungicides, however, some species present significant sensitivity to chemical products containing the active principle of the triazole group.