Abstract: In order to obtain strains with potential biocontrol ability against potato dry rot， NK-1, a strain with remarkable antimicrobial activity against Fusarium spp., was isolated using the plate confrontation assay in the present study. Strain NK-1 demonstrated antagonism against five pathogens, with inhibition rates of 47.31%-91.08%, and produced amylase, protease, and cellulase. Combined with morphological observations, physiological and biochemical characteristics, and multi-gene phylogenetic tree analysis, NK-1 was identified as Paenibacillus polymyxa. Through single-factor and orthogonal tests, the optimal fermentation components and conditions for NK-1 were determined as: 1% sucrose, 7% beef extract, 0.1% NaCl, 0.05% MgSO₄, temperature 28 ℃ , agitation speed 180 r/min, fermentation time 48 h, culture volume 50 mL (in 250 mL conical flasks), inoculum concentration 2.5%, and initial pH 8. Under these conditions, the biomass of NK-1 was approximately 60 times more than that obtained under pre-optimisation conditions. Additionally, its antimicrobial activity growth rate ranged from 4.16% — 17.23%. Moreover, the fermentation broth of NK-1 could induce deformation and disintegration of pathogenic hyphae. The germination rate of pathogenic fungal spores treated with 10⁸ CFU/mL of NK-1 fermentation broth ranged from 16.17%—24.50%. Results of the potato storage experiment showed that the NK-1 fermentation broth exhibited significant efficacy in controlling potato dry rot. The preventive and therapeutic effects were 30.10% and 23.01%, respectively, by day 30. This demonstrates that strain NK-1 possesses promising biocontrol potential against potato post-harvest dry rot, providing a new microbial resource for biological control of Fusarium dry rot.

Key words: potato dry rot, Paenibacillus polymyxa, optimization, storage, biocontrol effect