Screening And Identifying Of Antagonistic Actinomyce Against Phytophthora Parasitica Var. Nicotianae And Biocontrol Effects Of The Antibiotic

Tobacco blank shank (Phytophthora parasitica var. nicotianae)is one of the more important diseases during tobacco production. The tobacco area of blank shank disease is 76373hm2 and the yield loss is 2.86926×10⁷kg counting up to more than 1x108RMB per year in China. The norma1 control strategies are main in using chemical fungicides. Along with the appearance of environmental pollution caused by chemieal pesticide and 3R induding Resistance, Residue, Resurgence, Utilizing natural antagonistic microorganisms is a potential safe tool for crop protection and offers a promising altemative. Actinomycetes is important source with potential biocontrol effect.In this study, some actinomyces strains with antagonistic Phytophthora Parasirica were isolated from tobacco rhizosphere soil in main tobacco areas of ShanDong, the control efficacy at greenhouse experiment, taxonomic identifieation by analyzed, moreover, fermentation condition, stability of fermentation products and investigation of growth-promoting effect are studied. The main results are as follows:One hundred and twenty-five actinomycetes strains were isolated from different soil samples using dilution method. plant resist method combined with growth speed method were applied to screen antagonists. After primary selection by plate resist method, 8 strains were acquired. In the following screen, one strain named 97 showed the strongest inhibition activity with inhibition rate of 58%. The strain 97 and its crude antibiotic could not only inhibit the growth of the P. parasitica var. nicotianae, but also affect other thirteen Plant Pathogenic fungi, especially on Physalospora piricola, which inhibition rate is 58%.Its morphological, cultural physiological, biochemical characteristics, chemotaxonomy and 16S rRNA sequences analysis were studied. The substrate mycelium have no partition, the aerial mycelium are ramose. The mycelium of strain 97 was spiral and the spores are rod-shaped and the surface is smooth. The cell wall typeâ… and sugar type C showed the strain with Streptomyces character. The 16S rRNA sequence data confirmed the generic assignment. In the phylogenetic tree strain, 97 were most closely related to S. lavendulae, sharing 16S rRNA similarity value of 98.48%. Based on the polyphase taxonomical data, strain 97 was primarily identified as S. lavendulae.In order to increase the production of the fungicidal substance, the liquid media was optimized and the fermentation condition was primarily studied. The optimum fermentation medium of the 97 strain was composed of millet 10.0g, glucose 10.0g, CaC0₃2.0g, NaCl 2.5g, Peptone 3.0g. The optimum fermentation condition was as follows:seed age(36hrs), inoculation volume(6%), 50ml liquid medium in 250ml fiake, the initial pH of 7.0, at 28℃and shaked at 180r/min for 120h.The stability of the fermentation of strain 97 was studied. The results showed that it still had a high activity when stored up at 4℃, and was stable to acidic, neutral and heat, maintained the antifungal activity after treatment of proteinase K and ultraviolet radiation.The control efficacy to tobacco black shank and the promotion action to tobacco seedling in the seedling stage of the fermentation broth of biocontrol strain 97 was studied through the potted plant experiment and sand culture experiment. The result showed that 97 fermentation broths exhibited a good prevention action to the tobacco black shank. The ferment solutions diluted by 10 times may reach 70.9% to control tobacco black shank and displays the good stability. Moreover, fermentation broth with different concentration have influences on germination percentage, seedling height, seedling weight, root length, root weight of tobacco, the fermentation broth 10x could promote the growth of tobacco seedling largely.