Biocontrol potential of Bacillus pumilus HR10 against Sphaeropsis shoot blight disease of pine

Sphaeropsis shoot blight disease is caused by Sphaeropsis sapinea, a necrotrophic ascomycete pathogen. As severe damage and heavy losses from this disease have been documented in pine forests in many countries, an effective and environmentally friendly control strategy for Sphaeropsis shoot blight disease must be identified and the mechanisms involved determined. We performed research on the antagonism mechanism and biocontrol efficacy of Bacillus pumilus HR10 in plants because we found it to inhibit S. sapinea under in vitro laboratory conditions. The secondary metabolites secreted by HR10 led to mycelial deformities, delayed spore germination, and weakened mycelial growth of the pathogen. Additionally, the pathogen cell membrane was damaged, and mycelial cell content synthesis was disrupted by a HR10 culture filtrate. When HR10 colonized pine shoots, scanning electron microscopy indicated that it accumulated around the mycelium, reducing mycelial thickness, and assembled inside and outside of stomata, thus preventing pathogen hyphae from invading the needles. In a greenhouse experiment, HR10 exhibited a good preventive effect on Sphaeropsis shoot blight of Pinus massoniana, and 90% relative control was achieved by preventively spraying HR10 on pine shoots. The antagonistic substance was present in the 90% ammonium sulfate precipitate of a B. pumilus HR10 culture filtrate. Bacillus pumilus HR10 thus may be an effective and suitable biocontrol agent for shoot blight disease of pine. This study is the first report describing control of Sphaeropsis shoot blight disease by B. pumilus HR10 and illustrating how HR10 can efficiently protect P. massoniana from S. sapinea.