| Potato Late Blight is a kind of destructive disease that caused by Phytophthora infestans, which can lead to steams and leaves death and steam tuber rot. Its occurrence can cause serious losses. As its harm and difficult for control, the influnce of this disease on over the world is even much worse than Wheat stripe rust and Rice Blast Fungus, therefore, it is reagarded as the first worst crop disease in the world. Nowadays, the prevention ways on it includes cultivation measures, breeding for disease resistance, chemical pesticides and biological control. Especial for biocontrol has aroused public attention, for it is green and environmental protection-lasting.A strain NB-8 was obtained by Wang Yan in our laboratory in 2007, which had obvious inhibition effect to mycelial growth of Phytophthora infestans and the inhibition rate reached 92%. And antifugal substances produced by NB-8 might be water-soluble group of antibiotics in previous study. But at the later research that the inhibition effect of NB-8 on P. infestans was found, was not stable. Therefore, in this experiment, NB-8 strain was treated with LiCl, UV (ultraviolet radiation), and combining LiCl and UV, in order to get mutation strain, which can effectively and stablely inhibit P. infestans. And then the fermentation conditions of mutation strain were optimized, including inoculation amount, volume, time, orignal pH, temperature and rotational speed. In addition, inhibition way of mutation strain, the effect of inducing disease-resistant and suppression to other microorganisms were investigated. The main results were as follows:1. The original actinomycetes NB-8 strain was treated by LiCl, UV, combining LiCl with UV. Using P. infestans as indication fungus, we got 9 mutation strains, including 1 from LiCl, 2 from UV and 6 from combining LiCl with UV. Among them the LU-160 strain from combining LiCl with UV represented the highest inhibition effect, the inhibition effect of the fermented liquid (29mg/mL) was 73.13%, which increased by 15.66% in comparison with the original strain NB-8.2. After strain LU-160 was continuously cultured by 35 times, the inhibition effect still kept stable, the inhibition rate were 64% to 70%, which indicated that LU-160 had well genetic stability.3. The fermentation conditions of LU-160 was optimized with designed single factor experiment by filter paper method. The result indicated that the best inhibition effect to P. infestans was obtained in following fermentation conditions: inoculation amount 2%, inoculation volume 120mL/250mL, the natural pH, temperature 28℃, rotational speed 150r/min, time 8 d. Under the optimal conditions, concentration of the fermented liquid was 35mg/mL, and the inhibition rate reached 83.9%, which was 10.77% higher than that of the pre-optimization for fermentation conditions.4. The release and germination of zoospores of P. infestans were restrained by fermented liquid of LU-160, the inhibition rate was 94% and 40%, respectively. The effect of inducing disease-resistant to potato late bright on the detached tuber slices was rather obvious and the protecting effect was 65.39%.5. In the detached tuber slices of potato treated by fermented liquids (35mg/mL), in comparison with control, the activities of SOD declined, while PPO, PAL and soluble protein significantly increased.6. We investigated the inhibition effect of fermented liquid on 18 microorganisms. Only Botrytis cinerea in tested 9 fungi was evidently restrained by fermented liquid and the inhibition rate was 66.1%. There was no effect on the other 8 fungi. While fermented liquid displayed the obvious inhibition effect on 8 bacteria of tested 9 bacteria, including HT-6, Escherichia coli, Bacillus natto, Sporosarcina sp., Bacillus subtilis, YHX3, S341 and S343, and the diameters of inhibition zones were over 13 mm. |
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