Improvement of Sphaeropsis Shoot Blight Disease Resistance by Applying the Ectomycorrhizal Fungus <i>Hymenochaete</i> sp. Rl and Mycorrhizal Helper Bacterium <i>Bacillus pumilus</i> HR10 to <i>Pinus thunbergii</i>

Abstract

Ectomycorrhizal fungi (EMFs) form symbioses with plant roots to promote nutrient uptake by plants but it is controversial as to whether they induce disease resistance in plants. Here, we inoculated pine seedlings with <i>Sphaeropsis sapinea</i>, which was presymbiotic with the EMF <i>Hymenochaete</i> sp. Rl, and the mycorrhizal helper bacterium (MHB) <i>Bacillus pumilus</i> HR10, which promotes the formation of <i>Pinus thunbergia</i>-<i>Hymenochaete</i> sp. Rl mycorrhizae. The results showed that inoculation with <i>Hymenochaete</i> sp. Rl, <i>B. pumilus</i> HR10, and the consortium significantly reduced pine shoot blight disease caused by <i>S. sapinea</i>. After inoculation with pathogenic fungi, callose deposition was significantly increased in needles of pine seedlings inoculated with <i>Hymenochaete</i> sp. Rl, <i>B. pumilus</i> HR10, and the consortium, together with an increase in enzymatic and nonenzymatic systemic antioxidant activity as well as early priming for upregulated expression of <i>PR3</i> and <i>PR5</i> genes. Our findings suggest that ectomycorrhizal colonization enhances the resistance of pine seedlings to Sphaeropsis shoot blight by triggering a systemic defense response and that interactions between EMFs and MHBs are essential for mycorrhizal-induced disease resistance.