Screening And Applying Study Of Biocontrol Strains Of Streptomyces To Control Root-Knot Nematode

Root-knot nematodes (Meloidogyne spp.) constitute a major group of pathogens of important crops, and the biocontrol has been taken more and more attention recently. In this study, strain of JH108 of Streptomyces sp.was screened, which could control the root-knot nematode well in green house condition.303 Actinomyces strains were isolated from 41 soil samples which were collected from 29 sites covering Yunnan, Hainan, Jiangsu, Heilongjiang, Xinjiang, etc. Effect of their fermentation filtrate to second stage of Meloidogyne incognita (MI J2) was tested in vitro and in green house, and 15 strains whose 10-fold fermentation filtrate could konck down more than 70% of the MI J2 were selected. But only three of them could effectively control the root-knot nematode on tomato in green house condition. They are JH108,HJ103 and SX102. After inject 2 mL of the fermentation filtrate of the strains, the effect were 75.2%, 70.6% and 73.2% respectively. But only the strain of JH108 could keep the ability of producing nematicidal compounds after continuously transfer 4 generations. And the JH108 could be identified to red group of Streptomyces, based on its morphology, culture characters.In order to learn more about the JH108 for applying, the further study was carried out. Effect of fermentation filtrate of JH108 on the attraction of MI J2 to tomato root was tested on water agar plate. The filter paper strips soaking up with tomato roots extract or the fermentation filtrate were place on one side of water agar plate and the MI J2 suspension was inoculated on another side of plate at a 3.0cm distance. The results showed that MI J2 were attracted toward to the tomato root extract and repelled by fermentative filtrate of JH108 according the distribution rates of MI J2 on 0 - 1.0 cm area nearby filter paper strips. The MI J2 were significantly higher in the area treated by the root extract than that by fermentation filtrate or mixture of root extract and fermentation filtrate (P < 0. 01). The same result was obtained by using tomato roots or the roots dipped with JH108 fermentation filtrate (P < 0. 05). There was no significantly difference by placing the treated paper strips or roots at the same time or 24 h before MI J2 inoculation. It is deduced thatfermentation filtrate can obviously reduce the affinity between tomato root nematode and tomato roots,In order to improve the toxic effect on plant nematodes of culture filtrate of the JH108, fermentation media were optimized by using orthogonal design method. The optimized medium consisted of 20.0 g Soybean, 6.0 g (NH4)2SO4, 40.0 g Glucose, 3.0 g Peptone, 6.0 g Yeast extract, 0.6 g K2HPO4, 2.0 g NaCl , 2.0g CaCO3 per 1000 mL solution, and the pH value was 6.0. The effect of 10-fold diluted filtrate from the optimized medium was evaluated against MI J2. Compared to what produced using a traditional fermentation medium, the culture filtrate from the optimized medium was significantly more toxic to MI J2 of, killing 95.4% nematodes 24h after, up by 6.9%.Pot experiments were carried out to study the effect of biocontrol strain JH108 on controlling root-knot nematode of tomato with sterilized soil. The results showed that the effect of the dose of 3mL per tomato was the highest among four level dosage treatments, the different between the effect of 3mL and 4mL was not significant; the effect under the vaccination of MI J2 was higher that of eggs; the best time to inject the fermentation filtrate was the time of vaccination, and the significance level of the effects is 1%.The result of above studies showed that the JH108 could kill nematodes in vitro, and inhibited MI J2 invasion to tomato root intensively.