Study On The Mechanism Of Synergistic Induction Of Tobacco Resistance To Black Shank By Inducer And Arbuscular Mycorrhizal

Tobacco black shank is a soil-borne disease caused by the parasitic blight fungus,which is one of the most devastating diseases in tobacco production.While inducers can provide broad-spectrum disease protection for crops,they may also affect host growth and host-beneficial microbial interactions.In this study,two elicitors,β-aminobutyric acid（BABA）and methyl jasmonate（Me JA）,were selected to investigate their different methods of application in inducing persistent resistance in tobacco,the effect of both on the colonized root system of arbuscular mycorrhizal fungi（AMF）and the mechanisms involved in the synergistic induction of disease resistance in tobacco by BABA and AMF.1.The results of trials on different methods of application of BABA or Me JA in the induction of durable resistance in tobacco are as follows:Soaking seeds in 0.01mmol·L^-1BABA or 0.001mmol·L^-1Me JA solution for 1week improved the germination efficiency of seeds,promoted the growth of4-week-old plants,and induced resistance to tobacco black shank.The resistance of4-week-old plants to tobacco black shank could be induced by using sodium carboxymethyl cellulose and 1 mmol·L^-1BABA or 0.1 mmol·L^-1Me JA as seed coating agents.Sand culture with 0.5 mmol·L^-1BABA or 0.01 mmol·L^-1Me JA solution for 7days could induce the resistance of 1-week-old seedlings to tobacco black shank,and too high concentration would inhibit plant growth.When 0.5 mmol·L^-1BABA or 0.05mmol·L^-1Me JA solution was used for root irrigation,the colonization rate of AMF in tobacco roots was significantly increased and plant growth was promoted.The results showed that the commercial application of BABA and Me JA could not only induce long-lasting disease resistance of tobacco,but also promote root colonization and plant growth through plant beneficial microorganism AMF.2.The results of experiments to investigate the mechanisms associated with the synergistic induction of disease resistance in tobacco by BABA and AMF were as follows:After 35 days of AMF colonization,the colonization rate of plants only inoculated with AMF was 33.8%.The colonization rate of AMF was significantly reduced by 25.8%by P.nicotianae infection,and the colonization rate of AMF was increased by 35.8%by spraying BABA in the case of P.nicotianae infection.Both AMF and BABA reduced the disease index,and the disease index of tobacco plants treated with AMF or BABA was 43.3%and 36.3%lower than that of P.nicotianae alone.The disease index of tobacco infected by P.nicotianae treated with AMF and BABA was 70.3%lower than that treated with P.nicotianae alone.The control effect of AMF and BABA on tobacco infected by P.nicotianae was 50.6%and 36.3%higher than that of AMF or BABA and P.nicotianae.AMF and BABA treatments alone and in concert increased N,P,and K enrichment in leaves and roots,The two synergistic treatments significantly increased N,P and K contents in tobacco roots and leaves by 49.9%,148.2%,185.4%and 37.7%,237.4%,66.8%,respectively.It also increased the dry weight of the plant by 22.3%.Both AMF and BABA,alone and in concert,enhanced gas exchange parameters in plants infected with P.nicotianae,increased Pn,Gs and Tr parameters by 87.2%,204.8%and 31.1%,and reduced Ci by21.5%.Tobacco stem infection with P.nicotianae caused reduced root activity and increased the H₂O₂and MDA content in the leaves,whereas both AMF and BABA increased root activity by 130.1%and reduced the H₂O₂and MDA content in leaves of P.nicotianae-infected plants by 16.1%and 14.8%.Stem infection with P.nicotianae led to a reduction in the activities and transcription of SOD and APX and an increment in the activities and transcription of POD and CAT in the leaves.the AMF and BABA treatments,alone and in concert,enhanced the parameters for SOD,POD,CAT,and APX in the leaves,their synergistic treatment increased the activities of SOD,POD,CAT and APX by 114.1%,59.2%,104.3%and 498.1%.While It also resulted in the up-regulation of 2140.6%,91.3%,107.4%,1352.2%and 365.8%of related genes.Infection with P.nicotianae led to a reduction in the GSH and proline contents and increased the total phenol and flavonoid content in the leaves.AMF and BABA treatment,alone and in concert,led to an increment in the levels of GSH,proline,total phenolics,and flavonoids,their synergistic treatment increased the accumulation of GSH,proline,total phenol and flavonoid contents by 361.2%,237.9%,24.3%and 39.8%.Based on the above results,the resistance of tobacco plants to black shank induced by BABA and AMF may be due to the enhancement of plant photosynthesis,the increase of plant antioxidant enzymes SOD,POD,CAT,APX activity,the up-regulation of antioxidant enzymes SOD,POD,CAT,APX gene and black shank resistance gene Ph,as well as the increase of quality elements N,P,K content and antioxidant glutathione,total phenols and secondary metabolites proline,flavonoids content,and BABA and AMF synergistic treatment effect is better.In summary,our research can provide a reference for commercially viable BABA and Me JA application methods,which not only induce durable disease resistance in tobacco,but also promote plant growth and colonization of plant beneficial microorganisms AMF in roots.We have also found that the use of chemical inducers in the above-ground part in combination with inter-root inoculation of AMF significantly improves the immune response to disease resistance in plants,which provides some theoretical basis for further development of the use of green disease control agents.