Bacillus Manages Alfalfa Verticillium Wilt by Inducing Resistance, Enhancing Photosynthesis and Improving Quality

ABSTRACT

Alfalfa Verticillium wilt is a soil‐borne disease that severely limits alfalfa yield and quality, yet effective control measures remain scarce. In this study, four Bacillus strains (i.e., Bacillus amyloliquefaciens LYZ1125, B. velezensis LYZ1126, B. atrophaeus LYZ1127 and B. subtilis LYZ1128) were used singly or in combination to evaluate their biocontrol efficacy. In greenhouse, the strains reduced disease incidence by approximately 60%, decreased the disease index by about 80%, and achieved 80% control efficacy, significantly outperforming the chemical fungicides 0.0052 mg L ⁻¹ trifloxystrobin‐tebuconazole (60%) and 0.0446 mg L ⁻¹ azoxystrobin (30%). The biocontrol treatments promoted alfalfa growth, increasing plant height, stem diameter, root length, and dry weight per plant by 25%–37%, 20%–27%, 17%–48% and 39%–88%, respectively. Used singly or in combination, they also induced systemic resistance, with salicylic acid and jasmonic acid increasing by 15%–86% and over 33%, respectively. Net photosynthetic rate and chlorophyll content increased by approximately twofold and 4%–83%, respectively, along with enhanced peroxidase activity, while hydrogen peroxide and malondialdehyde accumulation decreased compared with the control. Alfalfa quality improved, with crude protein, soluble sugar, magnesium, and potassium increasing by 8%–30%, 3%–16%, 9%–22%, and 3%–14%, respectively, and reductions in acid and neutral detergent fibre. In the field, alfalfa Verticillium wilt occurred only in the control and thiram‐treated plots, with an incidence rate of approximately 1%. Bacillus mixture (1:1:1:1) outperformed single strains and controls, effectively managing wilt and promoting alfalfa growth via resistance and photosynthesis.