Screening and functional evaluation of strain HD9-1 against Streptomyces scabies

Abstract:

[Background] The soil-borne potato common scab (CS), caused by Streptomyces spp., is rampant in China, resulting in tremendous economic loss. With not efficient control measure available, the pathogen become more aggressive. Biocontrol bacteria which are environmentally friendly and show ideal effect in controlling the reproduction of the pathogen have attracted the interest of scholars. [Objective] To isolate and identify antagonistic bacterial isolate against Streptomyces scabies, determine the taxonomic status, evaluate the major biological traits, and thus to provide resources for the development of biocontrol agents. [Methods] Antagonistic isolates were screened from soil with high incidence of potato CS. The taxonomic status was confirmed with morphological, physiological, biochemical, and molecular methods. The control effect was analyzed by pot trials. Then, the potential application of the isolate was evaluated by broad-spectrum resistance (BSR) test, salt-alkali tolerance assay, and sensitivity tests to chemical fungicides. [Results] HD9-1 with significant antagonistic effect on S. scabies was screened out, which exhibited an inhibition zone diameter of 31 mm. The bacterial cells were rod-shaped and Gram-positive, with width of 0.75 μm and length of 1-2.5 μm. Colony of the isolate was yellowish, with smooth round edge. HD9-1 used sucrose as the only carbon source and produced β-galactosidase, arginine dihydrolase, lysine decarboxylase, and ornithine decarboxylase. IAA (3.44 mg/L) was detected in liquid medium after 24 h of culture. With the 16S rRNA sequence highly homologous to that of Bacillus subtilis RUB, HD9-1 was determined to be B. subtilis. The pot trial results showed that the scab-control efficiency was 59.15%. Under medium culture conditions, HD9-1 showed tolerance at pH 3.0-11.0, NaCl concentration of 1%-11%, and temperature of up to 100 °C (water bath for 30 min). This isolate was insensitive to zhongshengmycin, difenoconazole, fluconazole propamocarb, kasugamycin, flusilazole, pyrazole ether, azoxystrobin and thiophanate methyl. Meanwhile, it showed certain control effect on other crop pathogens, such as Verticillium dahliae, Fusarium oxysporum, and Rhizoctonia solani. [Conclusion] HD9-1, a B. subtilis strain, displays significant control effect on potato CS and strong adaptability, which can be a potential candidate for developing compound microbial agent against some potato soil-borne diseases.