Isolation and Identification of Pathogens Causing Soft Rot in Zhangxi Taro and Screening of Its Antagonistic Bacteria

Objective Taro〔Colocasia esculenta (L.) Schott〕is one of the important economic crops in Guangdong region. In recent years, taro soft rot disease has occurred frequently in Zhangxi area, Shaoguan, seriously affecting the quality and planting benefits of taro. Therefore, this study aims to explore the green prevention and control methods of taro soft rot.

Method Colonies with dominant growth were isolated from the bulbs of diseased plants by tissue isolation method, and pathogenicity was determined. The type of pathogenic bacteria was determined through colony morphology observation, determination of physiological and biochemical characteristics (including oxidase, indole determination, gelatin liquefaction, nitrate reduction, etc.) and 16S rDNA gene sequence alignment. In addition, antagonistic bacteria were screened from the rhizosphere soil of healthy taro by the decreasing dilution method and the plate confrontation method. Morphological characteristics, physiological and biochemical determinations, and 16S rDNA gene sequence analysis were conducted on the strains with obvious antibacterial activity to clarify the taxonomic status of antagonistic bacteria, and their optimal growth temperature and pH were determined.

Result Pathogenic strains were isolated from the bulb tissues of taro affected by soft rot disease. Pathogenicity determination confirmed that strain B1 was the pathogen of taro soft rot disease. Combined with morphological observation, physicochemical determination and molecular identification, it was determined that the pathogen was Dickeya fangzhongdai, with the optimal growth temperature being 28℃ and the optimal growth pH being 5.0. A biocontrol strain J1 with a significant inhibitory effect on taro soft rot pathogen was screened out from the rhizosphere soil of healthy taro. It formed a distinct inhibition zone, with an average diameter of approximately 18.3 (±0.6) mm in the plate confrontation test. It was identified as Bacillus subtilis, and the optimal growth temperature was 37℃. The optimal pH for growth is 7.0.

Conclusion The pathogen of soft rot disease of Zhanxi taro in Shaoguan is D. fangzhongdai. B. subtilis has antagonistic effect on this bacteria.