Screening, identification, and characterization of Streptomyces scabies antagonists

Abstract:

Potato scab caused by Streptomyces scabies has become a bottleneck threatening the sustainable development of the potato industry. Using biocontrol strains to combat bacterial infections is considered an ideal approach. [Objective] We screened the phosphorus-solubilizing antagonistic strains of S. scabies and investigated their effects on the prevention and control of potato scab, aiming to provide candidate strains for the development of composite functional bacterial agents. [Methods] The target strains were screened by plate confrontation and phosphorus-solubilizing tests. Their taxonomic status was determined by morphological observation, physiological and biochemical tests, and 16S rRNA gene sequencing. Pot and field experiments were carried out to measure the inhibitory effects of the target strains on S. scabies, and the relationship between phosphorus-solubilizing function and antagonistic effect was analyzed. [Results] Four antagonistic strains BN4-4, BN4-5, BN5-2, and YN17-2, were screened out. Among them, BN4-4 and BN5-2 showed strong ability to degrade inorganic phosphorus. BN4-4 and BN4-5 were identified as Bacillus atrophaeus, while BN5-2 and YN17-2 as Bacillus subtilis. The pot experiments showed that the relative control effects of the four strains were 71.35%, 38.70%, 62.18%, and 36.22%, respectively. In the field experiments, BN4-4 and BN4-5 showed the control effects of 69.07% and 56.20%, respectively. The four strains exerted inhibitory effects on four plant pathogens: Alternaria solani, Fusarium oxysporum, Rhizoctonia solani, and Verticillium dahliae. The four strains showed tolerance to pH 1.0–13.0, NaCl concentration of 1%–13%, and high temperatures (up to 80 ℃). Furthermore, they were insensitive to commonly used fungicides such as avermectin, zhongshengmycin, thiophanate-methyl, kasugamycin, and carbendazim. All the four stains exhibited the ability to metabolize and produce indole-3-acetic acid (IAA), which has been shown to promote the growth and increase the yield of plants. Notably, strains BN4-4 and BN5-2 capable of solubilizing phosphorus exhibited stronger inhibitory effects on S. scabies than the non-phosphorus-solubilizing strains. [Conclusion] B. atrophaeus BN4-4 with phosphorus-solubilizing function demonstrated promising preventive effects against S. scabies. This strain demonstrated broad-spectrum disease resistance, thermal stability, salinity tolerance, plant growth-promoting effect, and colonizing ability, serving as a potential functional strain for preventing and controlling potato scab and other soil-borne diseases in crops.