Screening And Evaluation Of Biocontrol Bcteria Against Rice Blast

Rice blast is a fungal disease causing serious damage to rice production worldwide.Using blast resistant varieties is the most economical and effective method to control rice blast.However,the pathogenicity of Magnaporthe oryzae is varying rapidly,often leading to loss of blast resistance.In addition,the application of synthetic fungicides is also a major method for prevention and control of rice blast,but the potential safety hazard stressed on environmental and food is worrying.In order to overcome these disadvantages,In vivo biocontrol and microbiological control is promising and becoming a research hotspot.In this study,we performed the screening and identification of biocontrol resource,testing of anti-fungal spectrum and greenhouse control effect.The main results were showed as follows:1.Screening and identification of biocontrol bacteria.In this experiment,483 strains were isolated from the rice leaves of Chaoyouqian cultivar in Luoxi Village,Gaoqiao Town,Taojiang County,Hunan Province.Using M.oryzae as the initial screening strain,124 strains with a certain inhibitory effect were obtained.Among these,bacterial strains RL1-15,RL1-16 and RL1-17 had significant inhibitory effects on the mycelia growth of M.oryzae,with inhibition rates of 88.84%,91.15%,and 89.24%,respectively.Strains RL1-15,RL1-16and RL1-17 were identified to be Bacillus via the observations of morphological,physiological and biochemical characteristics as well as the analysis of molecular 16S rDNA sequences.Among these,strain RL1-16 was identified as Bacillus amyloliquefaciens.2.Determination of the antibacterial spectrum of three biocontrol bacterial isolates.From the anti-fungal spectrum determination,we can conclude that strain RL1-15 had a certain growth inhibitory effect on other 7 tested pathogen fungi showing a highly inhibitory effects on Ustilaginoidea virens and Sclerotinia sclerotiorum,with the inhibition rates of76.57%and 63.35%,respectively.It also had moderate inhibitory effects on Gibberella fujikuroi,Rhizoctonia solani and cotton infected Fusarium oxysporum.Strain RL1-16 had inhibitory effects on 12 kinds of pathogenic fungi showing the highly inhibition rates of77.74%and 63.01%,to Ustilaginoidea virens and Rhizoctonia solani,respectively.It had the betterinhibitory effect of 73.03%on Sclerotinia sclerotiorum.In addition,the inhibition rates against to Botrytis cinerea strains,which infected Grape and strawberry separately,Alternaria alternata and Alternaria solan were 64.37%,72.38%,63.76%and 66.43%,respectively.Strain RL1-17 had highly inhibitory effects on Gibberella fujikuroi,Ustilaginoidea virens and Rhizoctonia solani,with the inhibition rates of 66.92%,79.50%and 65.90%,respectively.In addition,strain RL1-17 had the maximal inhibition rates of74.65%to S.sclerotiorum,61.68%and 60.62%to cotton and pepper infected Fusarium oxysporum strains,respectively.3.Determination of greenhouse prevention and control effects of the three biocontrol bacterial strains.All three bacterial strains have a certain control effect on M.oryzae.Compared to the water control group and 40%isoprothiolane,strain RL1-15 had the best control effect of 74.94%at the concentration of 2.0×10⁸ cfu/mL.Compared to water treated control and 75%tricyclazole,the RL1-16 had highly relative control effects of 88.37%and 86.93%when the bacterial suspensions were sprayed 3 days in advance at the concentrations of 2.0×10¹⁰ cfu/mL and 2.0×10⁹ cfu/mL,respectively.However,when treated 1d in advance,RL1-17 had a better relative control effect of 92.01%at the concentration of 2.0×10⁹ cfu/mL,followed by 90.34%at the concentration of 2.0×10⁸cfu/mL,which were similar to RL1-16 that showed a relative control effect of 90.19%at the concentration of 2.0×10⁹cfu/mL.Therefore,strain RL1-17 had a remarkable preventive effect on rice leaf blast,while strain RL1-15 had a significant therapeutic effect on leaf blast.4.Determination of the growth promoting effect of the three biocontrol bacterial strains.All three strains have a certain growth promoting effect.Compared with the clean water control,RL1-15 and RL1-17 had obvious growth promoting effects on rice plants that leading to plant increase when their concentrations were 2.0×10⁹cfu/mL and 2.0×10¹⁰cfu/mL,respectively.RL1-16 can increase the width of the stem base of rice,making the stems of rice plants thicker and less prone to be flattened.Compared with the chemical controls of isoprothiolane and tricyclazole,it had a certain promoting effect.The above-mentioned research experiments provided some certain guidance for enriching of the biological control resources of M.oryzae and a technical basis for the industrial production of biocontrol agents.