Biological characteristics of the pathogen of guava wilt and screening of biocontrol bacteria and control agents

Objective The biological characteristics of Nalanthamala psidii, a causal agent of guava wilt, were studied, and biocontrol bacteria and control agents were screened in order to investigate the occurrence rule and control strategies of guava wilt.

Method The biological characteristics of N. psidii GS-1 were detected under cultivation conditions with different carbon source, temperature, pH and NaCl concentration. The biocontrol bacteria for GS-1 was screened using plate confrontation method. The mycelial growth rate method was used to determine the inhibitory effects of six types of commonly fungicides on the pathogen.

Result The optimal carbon source for mycelial growth of GS-1 was fructose, and the optimal carbon sources for conidia germination were fructose and mannitol. The most suitable temperature and pH for mycelial growth were 30 ℃and 6 respectively. Plenty of conidia could germinate at the temperature of 28 to 46 ℃. The lethal temperature of conidia was 52 ℃. The GS-1 mycelia had certain degree of salinity tolerance. Bacillus amyloliquefaciens isolate B2 had the highest inhibitory effect on GS-1 growth. The GS-1 mycelia was the most susceptible to prochloraz and it did not grow when the content of prochloraz was 0.0004 μg/mL, followed by pyraclostrobin and metalaxyl with EC₅₀ of 0.4912 and 0.8805 μg/mL, respectively.

Conclusion The pathogen of guava wilt has a wide range of suitable habitat, and environmental conditions of higher temperature and neutral to weak acidity are conducive to its rapid growth and reproduction. Prochloraz, pyraclostrobin and metalaxyl can be used to control guava wilt.