Screening,Identification And Biocontrol Effect Of Antagonistic Bacteria Strain Against Potato Common Scab

Potato common scab,which caused by Streptomyces spp.,has been widespread occurred in major production areas of China in recent years.The disease brings damage increased year by year Significant chemical agents and measures have caused huge economic losses to growers and have become an important bottleneck restricting the sustainable development of the potato industry(especially the seed potato industry).It is an ideal way to prevent and control common scab by antagonistic microbial inoculant.The near-rhizosphere soil was collected from Zhaotong,Yunnan,where severe scab disease raged,and strains with antagonistic effects were isolated.Morphological observation,physiological and biochemical analyses,and 16S rRNA gene sequence determination were performed to characterize the strains isolated.The stability、bacteriostatic function and fermentation conditions of their metabolites were further examined,and the composition of its antibacterial substances was analyzed preliminarily.The main results are as follows:1.Colonies of strain YN-2-2 were circular,pale yellow in color,neat and smooth edges,dry surface,and middle depression.The strain was rod-shaped,with the size of 2.51-4.09×1.09-1.68 μm,gram-positive.And 16S rRNA nucleotide sequence was highly homologous to Bacillus thuringiensis.So this strain was identified as Bacillus thuringiensis.2.Pot experiments indicated that the disease index of common scab decreased significantly when potato plants were inoculated with 100 mL YN-2-2 culture with a final concentration of 1 × 107 CFU/mL,and the control effect was 36.11%.3.The best fermentation condition of YN-2-2:pH is 10.0,culture temperature is 28℃,inoculation amount is 2%,and culture time is 60 h.4.The secondary metabolites of YN-2-2 showed good thermal stability,a wide pH tolerance between pH 3 and pH 13,and low sensitivity to proteinase K.The diameter of the largest inhibition zone against Streptomyces sores was 22.8 mm.By comparing the anti-pathogen efficiency of ammonium sulfate extracted protein,we found that the best antagonistic efficiency was achieved under 80%saturation.