Mutation Improvement Of Streptomyces Platensis F-1 And The Biocontrol Potential Assesment Of Mutant Strains

Strepfomyces platensis F-1 is a biocontrol agents isolated from a health rice leaf. Previous studies showed that Streptomyces platensis F-1 has two antagonistic mechanisms. Firstly, Streptomyces F-1 could produce a broad-spectrum anti-fungal protein (AFP). Secondly, the volatile substances produced by Streptomyces F-1 could inhibit infection of rice leaves by Rhizoctonia solani, rapeseed leaves by Sclerotinia sclerotiorum and strawberry fruits by Botrytis cinerea.We used UV mutation and complex mutation of LiCl and UV to enhance the control efficacy of S. platensis F-1 and reduce the difficulty of the AFP'S separation and purification-The results are summarized below:1. We obtained seven significantly enhanced mutant strains by UV mutation. The seven strains were:UV-68, UV-30, UV-97, UV-63, UV-65, UV-52, UV-46. The inhibition zone between mutant strains and Botrytis cinerea were 9.9,10.0,10.3,10.4, 11.1,12.6 and 12.9 mm, respectively. The inhibition zone between wild strain F-1 and Botrytis cinerea was only 6.7 mm. The mutant UV-46 was the best strain with the inhibitory aactivity increasing up to 92.5%.2. We also obtained seven significantly enhanced mutant strains by complex mutation of LiCl and UV. The seven strains were:3-6,4-8,4-10,4-3,3-3,4-6 and 3-10. The inhibition zone between mutant strains and Botrytis cinerea were 16.2,16.7,16.8,17.1, 17.3,17.8 and 22.6 mm, respectively. The inhibitory zone for the mutant UV-46 was 12.9 mm. Mutant strain 3-10 showed a good potential for biological contro, in the dual culture experiment with Botrytis cinerea, the Botrytis cinerea hyphae was almost impossible to expand in PDA medium.3. The biocontrol potential of the three strains (F-1, UV-46,3-10) to control the postharvest botrytis fruit rot of strawberry has been assessed. The results demonstrated that:the control effect of the three strains to inhibit the Botrytis cinerea and control the postharvest botrytis fruit rot of strawberry was in turn enhanced. The disease severity of the strawberries soaked in the sterile water, PDB and cultural filtrates of three strains were 7.2,6.5,4.4,2.0,0.18, the control effect of mutant strain 3-10 was significantly better than wild strain F-1.4. The biocontrol potential of the three strains (F-1, UV-46,3-10) to control the Sclerotinia stem rot caused by Sclerotinia sclerotiorum has been assesed. The results demonstrated that the control effect of the three strains to inhibit the Sclerotinia sclerotiorum and the S. sclerotiorum infection was in turn enhanced. The cultural filtrates of mutant strain 3-10 diluted by 100 times still can significantly inhibit the S. sclerotiorum infection. Sprayed the cultural filtrates of mutant strain 3-10 could significantly control the occurrence of the Sclerotinia stem rot in the field.5. The biocontrol potential of the volatile substances produced by Streptomyces F-1, UV-46 and 3-10 has been assesed. The results demonstrated that the volatile substances produced by all of the three strains could significantly control the occurrence of the post-harvest diseases of green peper and the postharvest botrytis fruit rot of strawberry. The effect of the volatile substances produced by mutant strain 3-10 to control post-harvest diseases of green peper was significantly better than strains F-1 and UV-46. There is no significant difference of the three strains in control of postharvest botrytis fruit rot of strawberry.