Evaluation of Bacillus velezensis strain N23 for the control of potato common scab

Potato common scab (PCS) is a soil-borne disease caused by Streptomyces spp. It is a serious problem and S. galilaeus is the predominant causal agent of PCS in Inner Mongolia, China. Employing biocontrol agents to manage PCS represents a potentially effective approach. Consequently, there remains substantial room for the exploration of highly efficient biocontrol strains. To search for a better biological control agent in controlling PCS, 53 bacterial isolates were assessed for their suppression of S. galilaeus on oatmeal agar (OMA) plates. Among the isolates, strain N23 exhibited the highest level of inhibition against S. galilaeus PS1, with the total area of inhibition being 4.52 cm2. N23 metabolites in the fermentation broth inhibited PS1 with an inhibition zone of 2.54 cm2. N23 was identified as Bacillus velezensis based on morphological, physiological, and sequence analysis of 16 S rDNA and gyrA genes. Optimal conditions for N23 growth included soluble starch as a carbon source, ammonium nitrate as a nitrogen source, pH 7.5, and temperature of 32℃. N23 increased potato emergence and promoted the growth of potato plantlets. It exhibited 58.41% control of PCS infection in greenhouse trials. In two independent field trials, potato seed treatments with N23 resulted in PCS control ranging from 58.50% to 73.26%, and increased yield by 8.01% to 14.20%; while N23 soil treatments resulted in 56.77% to 66.30% disease control and a 3.32% to 18.10% yield increase. In this study, we isolated and identified a strain named B. velezensis N23, which can effectively inhibit the growth of S. galilaeus PS1. The results of greenhouse and field trials indicated that the strain could both inhibit S. galilaeus PS1 and promote potato growth. Thus B. velezensis N23 could be a promising biocontrol agent for the management of PCS.