Seleção de espécies de Bacillus para o controle biológico do oídio da videira

Abstract

Powdery mildew caused by Erysiphe (Uncinula) necator (Schw.) Burr. is one of the primary diseases of the grapevine (Vitis vinifera L.), and its control is mainly based on the use of synthetic fungicides. However, ecologically friendly control strategies with low risk of food contamination, such as biocontrol agents, have been employed. The objectives of this work were: 1. To evaluate and identify Bacillus isolates antagonistic to E. necator; 2. Characterize the adaptation of the antagonist isolates' to environmental and nutritional stress conditions; 3. Characterize the mechanisms of action of Bacillus isolates antagonistic to E. necator; 4. Evaluate the application of antagonist isolates in the integrated management of grape powdery mildew. In an initial screening using 45 Bacillus spp. from the Embrapa Semi-Arid Microorganism Collection, six isolates showed a reduction in disease symptoms greater than 70.0% on detached leaves. Two experiments in a greenhouse demonstrated that, when applied weekly, the isolates LCB03, LCB28, and LCB30 showed control efficiency greater than 80%. Sequencing of 16s rDNA showed that LCB03 showed 100.0% homology with B. velezensis, LCB28 99.93% with B. tequillensis, and LCB30 99.4% with B. siamensis. The isolates showed minor differences in the requirement of carbon sources, ideal pH range, glucose concentrations, and different nitrogen sources for their growth in culture medium and metabolized nitrate and ammonium as nitrogen sources. In an in vitro assay, LCB28 and LCB30 significantly inhibited conidial germination in co-culture and by producing volatile organic compounds. The potential to synthesize antifungal cyclopeptide was confirmed by PCR-based detection of gene markers for surfactin, bacillomycin, fengycin, and bacillysin production in the LCB28 genome, and the markers for all these compounds plus iturin in the LCB30 genome. Weekly alternating application of triflumizol and difenoconazole with the isolates LCB28 and LCB30 in a greenhouse reduced the incidence of powdery mildew by more than 70% and the severity by more than 90% on average in a greenhouse experiment. Two field experiments showed that powdery mildew incidence and severity were significantly reduced by applying formulations containing LCB28 or LCB30 in an integrated management strategy that replaced the concentration of synthetic fungicides, except during concentration and initial fruit growth, which are highly susceptible phases. The results of the experiments indicate that LCB28 and LCB30 have great potential to be applied in integrated powdery mildew management programs in grapevines.