Study On Screening, Identification And Biocontrol Effects Of Antagonistic Strains Against Fusarium Oxysporum F.sp Cucumerinum

In the process of protected vegetables cultivation, the number of harmful fungi in the soil increased with continuous cropping years increasing, but beneficial bacterium decreased, soil borne diseases endangers increasingly. Cucumber, as the main protected cultivation vegetable, is sensitive to continuous cropping. Cucumber fusarium wilt disease is the main soil borne disease in cucumber production, this disease endangers severely in condition of cucumber continuous cropping, even lead to no harvest. Based on solar greenhouse production practice in china's north region, this paper isolated, screened the effective antagonistic strains against Fusarium osysporum f.sp. cucumerinum from rhizosphere soil of continuous cropping cucumber, then classified and identified those strains, furthermore, studied the biocontrol effects of antagonistic strains against disease and their effects on growth and metabolism of cucumber, and their optimized fermentation condition. We also expected it could provide theoretical foundation and reference. Main results were as follows:1. A great deal of bacterium and actinomyces were obtained by isolating rhizoshere soil of protected continuous cropping cucumber. After repetitive co-culture on PDA plates, 10 strains, of which two are bacterium, the other eight are actinomyces, were screened for their stable antagonist toward Fusarium osysporum f.sp. cucumerinum, those strains named DS-1,Q-2,SZ-1,SZ-67,SG-126,SG-127,SG-147,SG-363,SG-494,ZL-1, respectively, and their inhibition rate toward Fusarium osysporum f.sp. cucumerinum reached to 30.5~45.5% on PDA plates.2. The results of germination tests and cucumber seedlings trails showed that, except SZ-67 restrain germination of cucumber seed, and SG-494 restrain growth of cucumber radicle , neither of the rest strains could produce bad effect on germination of cucumber seed, and DS-1,Q-2,SG-147,ZL-1,SG-127and SG-126 could also promote the germination of cucumber seed, at diffierent extent; those 10 strains gave significant protection against fusarium wilt of cucumber seedlings, their biocontrol effects reached to 55.56~88.89%, the effect of strain SG-126 was the best.3. The two strains DS-1, Q-2 were identified as Brevibacillus brevis and Lysobacter antibioticus by morphological, biochemical, physiolofical characteristics, as well as the 16Sr DNA sequence analysis. The GenBank accession number of two BCA is EF108303 and EF108304 respectively.4. Fermentation experiments showed that the optimized condition for DS-1 was the temperature at 28℃,pH7.0 and the oxygen was abundant; the optimized condition for Q-2 was the temperature at 28℃,pH8.0 and the oxygen was abundant; the growth curve of the two strains coincided essentially with typical growth characteristics of bacteria.5. DS-1, SG-126 and Q-2 could protect cucumber from Fusarium wilt and reduce its mortality, with biocontrol effects of 51.43%, 42.86% and 22.86%, respectively; DS-1 and SG-126 could significantly promote the growth and development of cucumber plants, however Q-2 made weaker effects; All the three strains could enhance the activities of SOD,CAT,PPO and PAL, as well as chlorophyll content of cucumber leaf at different extent, and decrease relative electrolytic leakage.