Biocontrol of black foot disease on grapevine rootstocks using Bacillus subtilis strain F62

Decline and death of young vines is a worldwide problem for viticulture that may lead to economic loss. Fungal pathogens have been associated with trunk and root diseases, including the black foot disease that affects the performance of the vineyards. Fungicides have not worked efficiently to control the disease and alternative methods should be investigated. We evaluated the potential of Bacillus subtilis strain F62 for controlling the disease caused by different strains in grapevine rootstocks 1103P (Vitis berlandieri × V. rupestris) and SO4 (V. berlandieri × V. riparia). The in vitro antagonism of B. subtilis F62 was evaluated on mycelial growth, by diffusible and volatile compounds, and conidia germination, by bacterial suspension and cell-free filtrate. In the in vivo assay, cuttings and micropropagated rootstocks were submitted to four different treatments: control, Bac (B. subtilis inoculation), Pat (pathogen inoculation) and Bac + Pat. According to our results, the bioagent was able to inhibit the mycelial growth of all the three fungal isolates by diffusible compounds and conidial germination by bacterial suspension and cell-free filtrate. In the in vivo assay, cuttings of SO4 treated with B. subtilis F62 showed higher shoot nodes and length of primary shoot, while cuttings of 1103P had a longer primary shoot. In micropropagated plants, B. subtilis F62 promoted plant growth in both rootstocks and reduced the frequency of D. macrodidyma re-isolation to 24.6% in SO4 and 29.5% in 1103P. The results demonstrated the potential of B. subtilis F62 on plant growth promotion and in the biocontrol of black foot disease on micropropagated plants and cuttings of grapevine rootstocks 1103P and SO4.