Isolation and biocontrol potential of Bacillus amyloliquefaciens against asparagus stem blight

Garden asparagus (Asparagus officinalis L.) is an economically important vegetable crop widely cultivated for its nutritional value and health-promoting properties. Asparagus stem blight, caused by Phomopsis asparagi (Sacc.) Bubák, is one of the most destructive diseases affecting asparagus production worldwide, leading to significant yield losses. In this study, a pathogenic strain of P. asparagi was isolated and characterized, serving as the target for screening antagonistic microorganisms from the rhizosphere soil of healthy asparagus plants. Among 79 isolates, one strain, identified as Bacillus amyloliquefaciens HN2-9 based on morphological, physiological, and molecular analyses, exhibited the strongest inhibitory activity against the pathogen. HN2-9 caused hyphal deformation, fragmentation, and lysis of P. asparagi. Optimal growth and fermentation conditions were established, achieving a maximum hyphal inhibition rate of 92.1% and spore germination inhibition of 54.8%. In greenhouse assays, HN2-9 significantly reduced disease severity on asparagus stems, with a disease index decrease of 72.4% at OD₆₀₀ = 2, without affecting seed germination or plant growth. These results demonstrate that B. amyloliquefaciens HN2-9 is an effective biocontrol agent against asparagus stem blight and provide a foundation for its development as a sustainable, environmentally friendly disease management strategy.