Biocontrol Effect Of Antagonistic Actinomycetes Against Phytophthora Nicotianae

Tobacco is one of China's important economic crops. In recent years, tobacco black shank has caused serious losses in the tobacco area of Chongqing. Biocontrol is an effective method in tobacco disease control, and actinomycete is an important source in biocontrol. In this study on Phytophthora nicotianae, the main works are the screening of antagonistic actinomycetes; antimicrobial activity of fermentation broth and fermentation stability and optimization of fermentation conditions.1. Thirty isolated laboratory strains of actinomycetes have been screened twice by using agar plates. First screening shows that 21 strains of actinomycetes have antagonistic activity on Phytophthora nicotianae, among which YSL 5-2 is the best antagonistic strain, reaching 36mm. Seven strains were be found with over 10mm inhibition radius. These 7 strains keep good antagonistic effect in the further screening, and the inhibition zone diameters ranged from 12 to 30mm.Those eleven strains of actinomycetes, which have been tested to have a better antagonistic effect by the method of inhibiting spore germination and inhibiting the growth of hypha, have inhibition on Phytophthora nicotianae. The research showed that the seven strains had antagonism against spore germination of Phytophthora nicotianae with over 50% and the inhibition effect of CWA-4, LZ 2-7, SYZ 2-6 were reached 100%.Eight strains had antagonism against hypha of Phytophthora nicotianae with over 80%, while five strains over 90% and the inhibition effect of CWA-4 was up to 96.97%.2. Determination of the antibacterial spectrum on the four strains which have a better antagonistic effect indicated that the four strains have good inhibition to 23 pathogens. LZ2-7, CWA-4 and YYZ-8 had good antagonistic effect on 5 pathogens with the inhibition zone over 15mm, and on 11 pathogens with the inhibition zone over 10mm.YSL5-2 had best effect on 22 pathogens with the inhibition zone over 15mm, among which eleven strains of the inhibition zone was over 20mm.3. To screening a better preservation way of antagonistic actinomycetes, five methods were used, naming Slope Preservation Act, Preservation Act of distilled water, Glycerol Preservation Act, Preservation Act of liquid paraffin covering and Preservation Act of sand tube. The test shows that six strains had the best antagonistic activity in the third month and seven strains showed best antagonistic activity in the ninth and twelfth month under the glycerol Preservation Act. So glycerol Preservation Act is better than others. However, the fifth preservation method is not stable enough because the antagonist activity had remarkably decreased from 3 months to 6 months.4. According to studying the fermentation condition of LZ 2-7, we determine the fermentation medium and the fermentation condition. Single factor fermentation test indicated that the best medium for fermentation:corn flour 10g,sugar 10g, sodium chloride 2g, ammonium sulfate 3g, calcium carbonate 2g, pH value of 7.2～7.4, distilled water 1000mL.and the best optimum conditions for fermentation is initiatory pH 7.0,28℃,250ml,250 r/min. culture time 5d.We use Phytophthora nicotianae as an indicator to determine the stability of fermentation of LZ 2-7 and CWA-4. The result showed the inhibition ratio of these 2 strains reduces with time increasing, which keep over 80% behind 30d but fell by about one-third after 90d.these 2 strains had a higher activity under 4℃,acidic or neutral conditions, and stable above 80℃in daylight, but decreased rapidly below 80℃with the heating time increasing or under UV irradiation, the Inhibition ratio of CWA-4 dropped to 2.66% under 121℃after 30min,or decreased by 27.84% under UV irradiation after 4h.5. Research of 2 actinomyces and its restraining function to Phytophthora nicotianae. The tests showed that there lied certain inhibitions of actinomyces on the growth of its mycelia,the germination of zoospores and The invasion of pathogens. The hypha showed depression dry,shrinkage,deformation dissolution and other phenomena after treated by actinomyces broth.6. Contrast of CK2,The results showed that the 4 strains of actinomycetes under five different treatments had good biocontrol effects against the Phytophthora nicotianae at the greenhouse experiment that the control efficiency of all achieved 50%,but the 4 strains had different control efficiency under differernt treatments, in that CWA-4 and LZ2-7 respectively up to 70% and 69% under every treatment.LZ2-7,CWA-4 and YYZ-8 had best efficiency could be up to 93.64%,96.18%,73.24% under the fifth treatment, and YSL5-2 could be up to 82.17% under the second treatment. Antagonistic actinomycetes had clear biocontrol effects against the Phytophthora nicotianae based on the statistical results after inoculated 7d,14d,but the control efficiency had a downward trend with the time being after 7d,except CWA-4 under the fifth treatment and YSL5-2 under the first treatment. All in all, CWA-4 under the fifth treatment is the best choice because of best efficiency and stability.The results showed the actinomyces broth of LZ 2-7 and CWA-4 which had the best control efficiency at the greenhouse experiment had good biocontrol effects against Tobacco Black Shank by the field plot experiment. Contrast of CK 2, the incidence of tobacco black shank from 46.67% dropped to 10% under the fifth treatment of LZ2-7. In the five treatments of LZ 2-7,the fifth treatment had best control effect with relative efficiency up to 74.32%,followed the third treatment and the first treatment, and LZ 2-7 had the better control effect of 27.03% than the control effect of 10.84% of CWA-4.