Isolation And Identification Of Antagonistic Strain Against Potato Bacterial Wilt And Its Effect On Soil Microbial Population When Applied To Soils

Potato bacterial wilt caused by Ralstonia solanacearum is one of the most serious diseases worldwide, and is reported to be one of the major limiting factors for potato production. Because the Ralstonia solanacearum is a soil-borne pathogen and can cause a systemic infection, it is difficult to control potato bacterial wilt. As the chemical control of the disease causes serious environmental pollution, the bio-control of potato bacterial wilt becomes an environmental, economic, and effective method. This paper primarily studies the biocontrol of potato bacterial wilt. The results are as follows:1. One Strain was isolated from soil and could effectively inhibit the potato bacterial wilt pathogen Ralstonia solanacearum. Based on morphological, physiological and biochemical characteristics and16S rRNA gene sequence analysis, the strain, named as strain T3, was primarily identified as Bacillus, sp. Genes sfp, fenB, mycB and ituA responsible for synthesis of antibiotics Surfactin, Fengycin, Bacillomycin, and Iturin were detected by PCR method in genomes of strain T3, which showed broad-spectrum antibiotic property, due to its antagonistic activities to multiple pathogens including bacterial and fungi pathogens. The strain T3could get the maximum growth under conditions as following, the temperature of30～37℃,volume of50mL/250mL, initial pH7.0, sucrose as carbon source, and peptone or yeast powder as nitrogen source.2. Pot experiment was designed to study the biocontrol and growth promoting effect of bio-organic fertilizer fermented by the strain T3(BF). Results showed that BF could increase the chlorophyll content, photosynthetic rate, stomatal conductance, intercellular CO2concentration of potato leaves, and significantly enhance the potato growth and increase the yield of potato. And the increased percentages by BF on potato plant height, shoot fresh weight, shoot dry weight and potato weight were45.3%,130.9%,129.7%and52.0%, respectively. Also BF showed extremely significant control effect on potato bacterial wilt with a biocontrol rate of79.4%, while the biocontrol rates of treatments T3(use strain T3only) and organic fertilizer (OF) were27.10%and30.84%respectively. And BF could significantly reduce the peroxidase activity and malondialdehyde content and improve the activity of superoxide dismutase in potato leaves.3. The microbial populations of potato rhizosphere was studied by plating count and PCR-DGGE methods respectively. Results showed that the cultured bacteria numbers of the four treatments all increased gradually until tuber formation stage and then decreased till harvest time. In treatment BF. strain T3could get a large number of colonization in potato rhizosphere soil, and significantly inhibit the growth of pathogen R. solanacearum, while treatments T3and OF could not inhibit the number of pathogen effectively. The results of bacterial community diversities analysis showed that, when compared with the treatment of CK, all treatments could improve the bacterial community diversity in a certain extent, and BF showed the most significant effect, the increased percentages in seedling period, tillering period, tuber formation period, mature period, and harvest time were12.80%,10.17%,14.15%,5.17%and9.49%, respectively. And fungal community diversities analysis results showed that organic fertilizer could increase the fungal diversity, while T3could inhibit the fungal diversity in a certain extent.