Screening Of Antagonistic Bacteria For Controlling Rice Bakanae Disease And Development Of Biological Seed Coating Agent

Rice bakanae disease（Rice bakanae disease）is an important seed-borne disease caused by Gibberella/Fusarum fujikuroi species complex（GFSC）.At present,the control of this disease is mainly based on the treatment of seeds with chemical agents,and the registration of biological pesticide seed coating agents has not yet been seen.In this paper,soil samples were collected from different regions to isolate and screen the strains that have obvious antagonistic effects on rice bakanae disease;at the same time,the seed coating agent auxiliaries were screened and optimized,the rice biological seed coating agent standard sample was developed,and its effect on rice bakanae disease was evaluated.In this study,432 bacterial isolates with different morphologies were isolated from 16plant rhizosphere soils in Jiangsu,Anhui and other places.The main species of the pathogenic bacteria of rice bakanae disease were Fusarium fujikuroi,Fusarium proliferatum,Fusarium graminearum and Fusarium asiaticum.Indicating bacteria,the inhibitory effects of 432 bacterial isolates and 42 antagonistic bacteria stored in the laboratory on bacillus were measured,and 18 biocontrol bacteria with good antagonistic effects were obtained.The 18 strains were molecularly identified through 16s r DNA sequence,and the related biological characteristics of 18 strains of antagonistic bacteria were analyzed and evaluated,such as swarming swarming ability,lipopeptide antibiotic production ability and spore forming ability.Through comprehensive analysis,5 strains of Bacillus were finally screened out:LSRS26,JTGSL12,ATFS18,JTRSM1 and RGQR43;and their effect on the control of bakanae disease at the seedling stage and the effect on rice growth were determined.The results showed that after seed soaking with the concentration of OD₆₀₀=1.0,the control effect of 5 strains of Bacillus and the reference strain Bs916 on rice bakanae disease was between 58%and 72%,among which JTGSL12,ATFS18 and Bs916 had the highest control effect,about is 72%.After soaking the seeds with the concentration of the bacterial solution OD₆₀₀=0.1,the control effects of the 5 Bacillus and the reference strain Bs916 were significantly lower than when OD₆₀₀=1.0,between32%～63%,of which ATFS18,LSRS26 and RGQR43 had better control effects,which were63%,49.45%,47.33%.In addition,LSRS26,JTGSL12,JTRSM1 and RGQR43 had a better promotion effect on the growth of rice buds after seed soaking with the concentration of OD₆₀₀=0.1.Among them,the strain RGQR43 had the most significant effect on the growth of rice,with an average bud length of 13.46 mm.In order to develop rice biopesticide seed coating agents,this study used the main film-forming agents,antifreeze agents,warning colors and preservatives in the reported seed coating agents as candidates to evaluate their compatibility with Bacillus.The results showed that the sodium alginate,polyvinyl alcohol,and gelatin in the film-forming agent had little effect on Bacillus.According to the influence of the film-forming agent on the survival of the strain and its various properties,sodium alginate:polyvinyl alcohol was selected for comprehensive analysis.（1:3）,gelatin:polyvinyl alcohol（1:3）,sodium alginate:gelatin:polyvinyl alcohol（1:1:1）as the combination ratio of film formers,and perform subsequent sample configuration and experiments;After screening,potassium sorbate or sodium benzoate were selected as preservatives,acid fuchsin was used as a warning color,and 1,2 propylene glycol was used as antifreeze.The color uniformity of the rice seeds with the combination film-forming agent and the warning color showed that the coloring of the seeds treated by the original solution was more uniform and brighter than that of the 5-fold dilution;in the treatment of the original solution,sodium alginate:polyvinyl alcohol=1:3 The coloring of the combination is the brightest.The effect of warning color of the combination film-forming agent on seed germination showed that the germination rate of sodium alginate:polyvinyl alcohol=1:3was equivalent to that of the water control,about 84%.That is,the combination of sodium alginate:polyvinyl alcohol=1:3 film-forming agent and warning color compatibility treatment has no effect on the germination of rice seeds.After the combination film-forming agent is combined with the warning color,the effect on the survival of the biocontrol bacteria is measured.The results show that the sodium alginate:polyvinyl alcohol=1:3 combination has the highest content of the biocontrol bacteria.The antagonistic strains were made into seed coating samples（3×10⁹CFU/m L）for seedling control effect evaluation.The results showed that the small sample products of strains Bs916,ATFS18,and JTGSL12 on rice bakanae disease were respectively 70.38%,61.40%,and 70.50%.In addition,this study also evaluated the compatibility of antagonistic antibacterial agents with commonly used fungicides.The study found that fludioxonil and metalaxyl have good compatibility with Bacillus and can be mixed with Bacillus preparations in production to improve the control effect of biological seed coating agents.