Identification and biocontrol potential of two antagonistic Bacillus strains against Phytophthora capsici

Abstract

Pepper blight caused by Phytophthora capsici L. is a devastating soil-borne disease in the pepper crop. Screening efficient antagonistic strains is one of the prerequisites for conducting research on the biological control of plant diseases. This study aimed to isolate Bacillus species against P. capsici. A total of 30 strains were isolated from three pepper-growing areas of Hainan province. Two strains, H12 and H23, exhibited significant antagonistic effects against P. capsici in the dual-culture assay with inhibition efficiency of 75.8% and 81.2%, respectively, and were selected as candidate biocontrol agents. Identification based on physiology and biochemistry charateristics, as well as 16S rRNA and gyrB genes, indicated that strain H12 belonged to Bacillus velezensis and was named Bacillus velezensis strain H12, whereas H23 was identified as Bacillus safensis, and named Bacillus safensis strain H23. Pot experiments showed that H12 and H23 provide potential resistance to pepper blight disease, reducing disease severity by 43.0% and 80.0%, respectively. Furthermore, strains H12 and H23 exhibited high hydrolytic cellulase and protease activities, which are associated with antagonistic activity against P. capsici. In addition, strains H12 and H23 induced PR1 and PR4 genes of pepper at 5 d post P. capsici inoculation, which is related to the salicylic acid (SA) and jasmonic acid (JA) signaling pathway. In conclusion, Bacillus velezensis strain H12, and Bacillus safensis strain H23 may serve as potential biocontrol agents and provide a theoretical basis for preventing and controlling pepper diseases.