Screening And Identification Of Antagonistic Strains Against Fusarium Graminearum

Fusarium head blight or scab of wheat and barley caused by the Fusarium spp, which is the major disease in China and other countries in the world. Fusarium head blight not only reduces the yield, but also produces harmful fungal toxins to human and animals, entering into the food chains, affecting food safety. Over many years, scab has been controlled by chemical-based methods, and thus fungicide-resistant Fusarium strains have emerged. Therefore, the screening and purification of Fusarium antagonistic bacteria, as well as isolation and identification of new biological fungicides are important for controlling the scab disease. This study was designed to isolate antagonistic microorganisms from the plants and soil and to identify their antagonistic substances. The isolated bacteria showed a good inhibitory effect on Fusarium graminearum.From healthy wheat ears and soil in heavy FHB epidemic areas in Hubei, a total of 881 isolates were purified. After screening 18 bacterial strains showed inhibitory effects on Fusarium graminearum with an inhibition rate being more than 50%. Two strains with the highest antagonistic activities were selected for fermentation, and the fermentation broth of the strains showed a broader spectrum of antagonistic activities. Furthermore, after ammonium sulfate precipitation the antagonistic substances from these two strains showed that the inhibitory effects mainly as follows:inhibition of mycelial growth of Fusarium graminearum, causing distorted hyphae, local swelling of conidia and reduced germination rate.Antagonistic strains S76-3 and X-42 can protect wheat seeds, and has a role for controlling scab in field. For treatment of wheat seeds with antagonistic fermentation broth of two bacterial strains,the seeds were first inoculated by spores of F. graminearum, and the results showed that there is no significant differences of seed germination between the treated seeds and controls with no inoculation of Fusarium spores, indicating that antagonistic bacteria can protect the normal germination of seeds. Field experiment results showed that antagonistic strains S76-3 and X-42 and their mixture showed significant protection of wheat spikes, with relative control efficiency up to 72.3%. It has the same controlling effect with 50% carbendazim (800 times dilution) at the?=0.01 level, and this controlling effect is good. Application of the antagonistic bacteria in the spikes before and after spraying of Fusarium spores have a good protective effect, and the results indicated no significant difference between the treatments of before and after spore inoculation. Based on morphological characteristics,16S rDNA sequence analysis and specific primer analysis, the two strains S76-3 and X-42 belong to Bacillus amyloliquefaciens. Through optimization of fermentation conditions, these two strains were found to have good antimicrobial efficacy in the best medium for Landy, pH 7.0, at 28?for 48 h and the secretion of antagonistic substances were preliminarily identified as lipopeptide, and the crude lipopeptide extracts were insensitive with the temperature and proteinase K.