A Herpetosiphon llansteffanensis Strain from Forest Soil Exhibits Biocontrol Activity Against Pear Fire Blight

Fire blight, a devastating bacterial disease caused by Erwinia amylovora, has posed significant challenges to apple and pear production for over a century. This study introduces a gliding filamentous bacterium, the strain NSD29, isolated from natural forest soil in Xinjiang, China, as a biological control agent for managing this disease. Comprehensive characterization based on morphological, physiological, biochemical, 16S rRNA gene, and whole-genome analyses identified the strain NSD29 as Herpetosiphon llansteffanensis. The train NSD29 demonstrated potent predatory activity against E. amylovora in vitro. Its biocontrol efficacy was subsequently evaluated on detached leaves, inflorescences, young fruit, and shoots of fragrant pear under controlled greenhouse conditions. Results indicated that applying H. llansteffanensis NSD29 significantly inhibited lesion expansion on pear leaves and young fruit, achieving protective efficacies of 75.2% and 72.0%, respectively. Furthermore, pre-treatment spraying with NSD29 effectively reduced the incidence of blossom blight, with a control efficacy of 61.2%. On detached pear shoots, the application of NSD29 fermentation broth suppressed lesion expansion, demonstrating substantial protective (86.8%) and curative (75.6%) efficacies. This research provides the first evidence for the potential of Herpetosiphon species in the biological control of plant diseases, highlighting H. llansteffanensis NSD29 as a promising candidate for developing strategies to combat fire blight.