Biocontrol Effect And Mechanism Of Bacillus On Tomato Early Blight And Tomato Yellow Leaf Curl Virus Disease

Bacillus as an important type of biocontrol strain has the advantages of fast growth,simple nutrition,strong resistance and wide distribution.It is very important to obtain excellent strain resources and further study the biocontrol mechanism.The previous research of our group found that Bacillus laterosporus Bl13 had a significant inhibitory effect on the pathogen of Tomato early blight,but there was no further validation of the effect of Bl13 on the control of Tomato early blight,and the mechanism of its control by Bacillus was not clear.In addition,the previous study of our group found that the application of Bacillus amyloliquefaciens Ba13 could increase the gene expression related to induced systemic resistance in tomato plants,and significantly reduce the susceptibility of TYLC V(Tomato yellow leaf curl virus)and the disease index of susceptible plants.RNA interference(RNAi)is a special natural defense system for plant to resist virus invasion.It is not clear whether the antiviral effect of biocontrol bacteria is related to the regulation of RNAi by Biocontrol bacteria.The main results are as follows:(1)In this study,through screening and identification of 10 strains of Bacillus preserved in the laboratory,2 strains of excellent Bacillus MY1 and CY1 with growth promoting and broad-spectrum bacteriostatic functions were obtained,and MY1 was identified as Bacillus velezensis,CY1 is Bacillus subtilis subsp.inaquosorum.After inoculated with MY1 and CY1,the plant height,stem diameter and dry weight of aboveground part of tomato were significantly increased,the dry weight of tomato aboveground parts increased by 30.57% and 17.22% respectively.After 30 days and 60 days of inoculation with MY1,the activity of PAL(phenylalanin ammo-nialyase),PPO(polyphenol oxidase),POD(peroxidase),and C AT(catalase)can be significantly increased;after 30 days of inoculation with CY1,PAL can be significantly increased,PPO,CAT three kinds of defense enzyme activity.The results showed that MY1 and CY1 can promote tomato growth,enhance tomato plant resistance,and have potential biocontrol characteristics.(2)Through pot experiment,it was confirmed that Bl13 had good control effect on Tomato early blight,and the related mechanism of Bl13 to control tomato early blight was preliminarily explored.After applying Bl13,the disease severity of infected plants was significantly reduced,and the relative control effect reached 26.67%.The activities of PPO,POD and other defense enzymes in leaves were improved,and the effect of the disease on the growth and development of aboveground parts and roots of plants was reduced.The average total root length and average root volume of tomato plants in the Bl13 treatment group increased by 32.87% and 35.63% compared with the control group.The application of Bl13 increased the relative abundance of Bacillus and Pseudomonas by 110.54% and 102.27% respectively,and decreased the relative abundance of Olpidium and Haematonectria by 26.47% and 86.28% respectively.(3)Based on the analysis of m RNA and small RNA,the mechanism of biocontrol bacteria Ba13 on the RN Ai of plant antiviral system was preliminary explored.Ba13 can improve the key factors of RNAi silencing complex AGO1,AGO2 by adjusting the mi RNA abundance such as mi R168,mi R403 Expression enhances the plant's ability to eliminate viruses,and at the same time reduces the abundance of si RNAs such as si RNA5327 and si RNA5429 that completely match the viral genome.In addition,Ba13 can enhance the expression and synthesis of tomato photosynthetic system and growth regulation related hormones such as auxin and brassinosteroids,activate the systemic Acquired Resistance(SAR)pathway of the leaves and increase the content of SA a nd ABA in leaves,and regulate the synthesis of antiviral and antioxidant related substances such as diterpenoids and selenium compounds.The results indicate that Bacillus amyloliquefaciens Ba13 can enhance plant resistance to TYLC D by enhancing plant antiviral system RN Ai and affecting plant growth regulation and resistance pathways.In summary,this study provides new strain resources for using microbes to promote plant growth and enhance plant resistance.It initially revealed that the improvement of rhizosphere microecology by Bacillus is closely related to the prevention and treatment of Tomato early blight.From the perspective of RNAi,we explored the mechanism of spores in preventing and controlling viral diseases,and provided new research ideas for the study of the "plant-microbe" interaction mechanism.