Screening and characterization of endophytic Bacillus for biocontrol of grapevine downy mildew

Grapevine downy mildew, caused by Plasmopara viticola, results in a serious and persistent disease problem for the grapevine industry worldwide and is difficult to control through chemical and agricultural means. The aim of this study was to screen bacterial endophytes with potential applications for biocontrol of this disease. A total of 239 bacterial endophytes were isolated from grapevine leaves and screened by leaf disk assays. Two strains, GLB191 and GLB197, which exhibited the most robust preventive effects against P. viticola, were tested in the field during two successive years (2013-14). The results demonstrated a dramatic decrease in disease severity after eight spray treatments, suggesting both strains as potential biocontrol candidates for P. viticola. The 16S rDNA and the gyrA/gyrB gene analysis identified GLB191 and GLB197 as Bacillus subtilis and B. pumilus, respectively. Confocal microscopy showed that both endophytes could recolonize grapevine leaves. This study is the first to demonstrate that endophytic Bacillus can inhibit grapevine downy mildew disease. (C) 2017 Elsevier Ltd. All rights reserved.