| Potato Late Blight is a kind of destructive fungal disease that caused by Phytophthora infestans, which can lead to steams and leaves death and steam tuber rot.The occurrence of it can cause serious cuts. As its harm, controling difficulty and even worse than Rice Blast Fungus and Wheat Stripe Rust, it is reagarded as the world’s worst crop disease. So the effective control of it has become a serious problem in potato production. Nowadays, the prevention of it includes breeding for disease resistance, cultivation measures, chemical pesticides and biology control, particularly biocontrol for it is green and lasting. From the view of biocontrol, according to the study in our lab that the inhibitory activity of the mixed fermentation of Alternaria alternata and Alternaria brassicae was better than that of single fermentation, and mixed fermentation liquid could inhibit P. infestans strongly at low concentration, on the other hand, three actinomycetes from the soil which had significant inhibitive function on the growth of P. infestans was filted, the best enviroment of mixed fermentation of two fungi and three actinomycetes against P. infestans was optimized in this experiment, and the physical and chemical properties of fermentation liquid, the inhibition on spore germination, the induced resistance were also studied.The reasults were as follows:1. The order of inoculation of mixed culture of two strains were that after A. brassicae was inoculated in the medium and cultured for 24h under 25℃,then A. alternata was inoculated and mixed cultured for 6 d. The favorable fermentation conditions was the proportion of the two fungi was 1:1. It was demonstrated that the concentration was 5.3 mg/mL, and using 40μL, the inhibitory rate was higher than 86%. It was better than the effect before optimaizaion (7 mg/mL, using 100μL and the inhibitory rate was 92.15%).2. The results showed that the mixed fermentation liquid of A. alternata and A. brassicae could keep stability under natural light and ultraviolet rays. After dealed by natural light for 6 h, 12 h, 18 h, 24 h or ultraviolet rays for 30 min, 2 h, 6 h, and 10 h, the inhibitory rate was more than 80%. The active substance was non-protein and its polarity was weak.3. Experimental in vitro tissue that dealed by the mixed fermentation liquid of A. alternata and A. brassicae showed that the effect of treatment (Disease index 20) was better than prevention (Disease index 100) on potato leaves, but opposite on potato tuber slice that disease index of treatment and prevention was 8 and 85, respectively.4. There were no obvious antagonistic among the three actinomyces strains, and the best ferment combination mode was that NB-8 was inoculated at first, NB-11 and NB-12 was inoculated 2 days later and then mixed fermented for two days. Whose effect was higher than that of any single ferment. The inhibitory activity was the highest at pH8 and 28℃. The inhibitory rate of this ferment mode was 97.7% and much better than that of any single ferment, inhibitory rate of NB-8, NB-11, and NB-12 were 87.4%, 20.0%, and 28.2%, respectively.5. The mixed fermentation liquid could keep stability under 30~105℃for some time and the inhibitory rate keeped higher than 80%. After dealed by natural light for 6 h, 12 h, 18 h, and 24 h, the inhibitory rate was more than 85%. Additionally, after dealed by ultraviolet rays for 30 min, 2 h, 6 h, 10 h, the inhibitory rate was more than 79%. So it was strongly bear of heat and light.6. The mixed fermentation liquid of the two fungi against P.infestans could keep inhibitory activity for 7 days, but the mixed fermentation liquid of the three actinomycetes was shorter.7. It was preliminary clear by experment that release and germination of zoospores were restrained and the mycelium was deformed.It concluded that there was a negative correlation between the activity of SOD and resistance to Potato Late Blight, and there were positive correlation between the activity of PPO and soluble protein content and the resistance to Potato Late Blight, and showed defence mechanism. |
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