Rice husk biochar suppresses white root rot disease caused by Rosellinia necatrix in Japanese apricot trees independent of arbuscular mycorrhizal fungi and bahiagrass

White root rot caused by Rosellinia necatrix severely affects Japanese apricot productivity. In this study, rice husk biochar (CN ratio 102.06, pH 7.8) was evaluated for its disease-suppressive effects, alone and in combination with arbuscular mycorrhizal fungi (AMF) and bahiagrass (Bg), in sterile conditions. In vitro assays revealed that neither rice husk nor bamboo biochar inhibited pathogen growth, with hyphal expansion reaching 22 % higher than control at maximum Brh concentration. However, in vivo, biochar treatments significantly reduced disease severity: rice husk biochar decreased white root rot severity by 25 % at 26 days; BrhAMF by 20 %. Disease scores at 12 days post-inoculation were 2 ± 0.7 (Brh), 1.5 ± 0.3 (BrhAMF), compared to 4.2 ± 0.25 in controls. Plant growth was positively affected: fresh biomass increased by 79.4 % (AMF), 125.4 % (BrhAMF), and 62.2 % (BbAMF) vs. control. Shoot weights in the BrhAMF group reached 26.6 g versus 19.15 g for AMF alone, indicating enhanced nutrient availability. Leaf nitrogen content was 0.35 g in BrhAMF and 0.34 g in AMF-only plants, while leaf phosphorus rose to 0.027 g in BrhAMF, compared to 0.01 g in controls. Mycorrhizal colonization dropped from 50.4 % in AMF to 27 % with combined BrhAMF, likely due to increased leaf P. Overall, rice husk biochar efficiently suppressed white root rot independently of AMF and Bg, mainly through physicochemical soil effects and improved plant nutrient uptake, demonstrating its potential for sustainable disease management in perennial orchards.