Screening Strategy Of Biocontrol Agents Against Ralstonia Wilt On Ginger And Its Impacts On The Rhizosphere Environment

Ralstonia solanacearum Yabuuchi et al is one of the most destructive soil-borne plant diseases which distribute from tropical, subtropical areas. It has a wide host range of more than300species from50families. So far, Ralstonia wilt control approaches, including field sanitation, crop rotation and application of resistant varieties, as well as chemical pesticides has limited effectiveness. However more and more attention was paid on biological control which considered being no pollution, no harm to human being and animals, and environment-friendly. Several products have been commercialized in China and abroad. But biocontrol used in practical farming was not as much as chemical pesticides. The reason for its difficult to accept is unstable in practical produce. Here we aim to develop a new and reasonable screening strategy of antagonists against Ralstonia wilt on ginger. The colonization ability of the applied BCAs and its impacts on the bacterial community structure and environment were evaluated.1. Screening and evaluation of the antagonists against Ralstonia wilt on gingerIn this study, we have isolated420strains first. All the strains were isolated from stem, leaf and root of healthy ginger plants from a serious infested field in Shandong province, which is one of the most productive provinces in China. Eighty-five strains were obtained base on the in-vitro antagonistic activity and ability to produce related enzymes. Then these strains were analyzed by ARDRA and BOX-PCR. Nineteen strains from different BOX clusters were applied in in-vivo antagonistic test in greenhouse. Among them,4strains showed significant biocontrol efficacy that more than50%(1JN2:Bacillus subtilis-,5YN8: Bacillus amyloliquefaciens;3YW8:Myroides odoratimimus and2JW6:Stenotrophomonas maltophilia). The highest biocontrol efficacy69.17%was obtained by1JN2. This is the first report which used Myroides odoratimimus and Stenotrophomonas maltophilia as biocontrol agents against Ralstonia wilt on ginger.2. Establishing a new screening system for antagonists against Ralstonia wilt on gingerIn order to develop a new and reasonable screening strategy we had to give different values to the19BCAs that applied in greenhouse test according to their in-vitro antagonistic activities and ability to produce related enzymes. Coincident relationship between the assessment values and the actual biocontrol efficacy was calculated, which can reach0.87. Activities of the BCAs that had assessed values include protease activity, chitinase activity, cellulase activity, glucanase activity, siderophores activity and in-vitro antagonistic activity. Several reports considered that iron competence is much more important between bacteria. So the siderophores activity in this study was given double value. According to the results we can see that this assessment was reasonable enough and efficiently.3. Impacts on the rhizosphere bacterial community structure and environment of the applied BCAsIn this study, PCR-DGGE of the rhizosphere soil samples was done to detect the impacts on the bacterial community structure and the colonization ability of the applied BCAs. The content of organic matter, available N、P and K was compared between different treatments.Based on the results, all the applied BCAs could colonize on the rhizosphere effectively at60days post treated. Additionally, B1301(Bacillus megaterium)、AR156(Bacillus cereus)、SM21(Bacillus subtilis) could colonized effectively at120days post treated which covers the whole grow period of ginger. And the rhizosphere organism diversity was enhanced after treated by the BCAs.After compared the content of organic matter, available N, P and K between different treatments we can make a conclusion that treatment of1JN2enhanced the content of organic matter and available N、P and K significantly. It may due to the potential ability to fix N, P and K by the strain. 4. ConclusionWe have gotten some new findings as followed:First:4effective BCAs were obtained; this is the first report which used Myroides odoratimimus and Stenotrophomonas maltophilia as biocontrol agents against Ralstonia wilt on ginger. Second:an assessment was established to screening antagonists against Ralstonia wilt on ginger. Third: colonization ability and impacts on the bacterial community structure was evaluated by DGGE.However there are some shortages in this study:The assessment system did not evaluate by other plant pathogen and the mechanism of the applied BCAs needs to determine.