Study On The Isolation, Selection And The Antagonism Of Soil Actinomycetes WM2-4

The isolation and screen of antagonistic actinomycetes with great activity on plant pathogens, such as Pyricularia grisea were carried out. The identification of the antagonistic strain, optimization the fermentation conditions and separation of the active compounds were studied for the biological control of plant diseases.(1) Four hundred and thirty-three antagonistic strains were isolated from forty eight soil samples collected from different areas of China by diluting method. Thirteen actinomyces had been proved to have antagonistic activity by confronting cultivation on PDA plates, which amounted to 3% of the total separation. Among them, the strain WM2-4 exhibited the strongest antibiosis capacity with an inhibition zone of 22.2 mm on Pyricularia grisea, the ferment filtrate also showed the best inhibitory effect with 89.4% inhibition rate by mycelium growth rate method and the inhibition zone was 32.5 mm. by cylinder plate method.(2) The strain WM2-4 was identified as Streptomyces galbus on the morphological, cultural, physiological, biochemical characteristics, 16S rDNA gene sequence and phylogenetic analysis.(3) The strain WM2-4 possessed a wide antagonistic effect on many pathogens, such as Botrytis cinerea, Rhizoctonia cerealis, Sclerotinia sclerotiorum, Alternaria solani, Fusarium moniliforme, Fusarium graminearum, Fusarium solami, Pyricularia grisea, Bipolaris sorokiniana, Fusarium avenaceum, Rhizoctonia solam and Fusarium oxysporum.(4) The optimal fermentation condition for strain WM2-4 was studied. The results showed that the optimal condition was as follow: medium's initial pH at 7.5, in 500 mL flask with 100 mL medium, the inoculation amount 6%, ferment for 5 days, with the inhibition rate of 69.2% on Pyricularia grisea.(5) The metabolic products of strain WM2-4 were separated on silica gel column chromatography with acetone / cyclohexane (1:7) as eluent, and the metabolite exhibited strong antibiosis capacity with an inhibition zone of 33.0 mm on Pyricularia grisea at a concentration of 1 mg/mL.