| Serratia plymuthica A21-4,a PGPR strain isolated from rhizosphere soil of onion,has strong colonization capacity and antibiotic activity to pathogen and significant effect of promoting growth and induced resistance and so on.In order to further confirm effect of promoting pepper growth and induced resistance by A21-4,and explain their mechanism,A21-4 promoted pepper growth,and effect of rhizosphere soil microbial ecology were investigated adopting field experiment,analyzed mechanism of promoting pepper;in order to confirm effect of Induced Systemic Resistance by A21-4,this paper measured disease index of P.capsici and anthracnose after inoculation in vitro and natural disease in the field;Meanwhile,this paper studied the changes of activity enzymes related to defense response,and the signal transduction pathway of induced systemic resistance by A21-4.Results were as follows:1.Through field experiment,treatment with A21-4 significantly enhanced stem diameter,chlorophyll content and root activity of pepper in adult stage,increasing rate was 23.66%,56.26% and 50.32-237.13%,respectively,compared with those under control;moreover,yield of pepper increased 44.55% after treatment with A21-4;then,protein content,vitamin C content and nitrate nitrogen content were all significantly increased up to 29.32%,53.97% and 129.84% in pepper fruits respectively.2.A21-4 has a strong colonization capacity,and significantly enhanced soil enzyme activity and available N,P,K content.Transplant after irrigating root treatments with A21-4 concentration of 108 cfu/m L,the concentration of A21-4 in the root and soil were maintained over 105 cfu/g from 30 to 70 days;moreover the catalase activity of rhizosphere soil was significantly increased by 22.95-32.31%,urease activity was significantly increased by 24.32-94.11% and phosphatase activity was significantly increased by 49.41-271.74%;A21-4 also significantly increased available N content,available P content and available K content,increasing rate was 7.60-49.25%,7.24-17.93% and 12.70-25.61%;In addition,treatment of A21-4 was significantly increased the number of rhizosphere soil bacteria and actinomycetes,but significantly reduced the number of rhizosphere soil fungi.3.A21-4 could induce resistance against phytophthora capsici and anthracnose of pepper in the context of in vitro inoculation and natural disease in the field.The control efficiency of leaves and fruits in vitro against phytophthora reached up to 32.30% and 52.16%,respectively;the control efficiency of fruits artificial inoculation in vitro against anthracnose reached up to 42.97%,and in the field reached up to 62.10%.4.A21-4 could significantly enhance defense enzymes and PR protein activity.Activity of POD,PAL and PPO went up evidently,improved 330.88%,14.93% and 68.18%;moreover the activity of ?-1,3-glueanas and chitinase significantly increased up to 23.13% and 224.19% respectively.Preliminary inference,A21-4 induced resistance was closely related to increase of all five enzyme activity.5.Expression quantity of regulator genes related to signal transduction pathway in pepper of induced systemic resistance by A21-4 was researched by RT-PCR and Real-time PCR.The results suggested that A21-4 induced the over-expression of genes NPR1 and PR1,as regulatory genes in SA signal transduction pathway,whereas,gene PDF1.2,as a JA/ET signal transduction pathway modify gene,was weakly detected or not expressed,and the expression of Ca CYP1 and Ca BPR1,which were involved in SA-and SA-,ET-mediated signaling pathways,were strongly induced in plants treated with strain A21-4 as compared to water-treated control plants,however genes involved in the JA-and ET-dependent signaling pathway(Ca PR4 and Ca PR10)did not differ among treatment conditions.These results indicated that the priming of NPR1,PR1 and Ca CYP1 expression by strain A21-4 plays a role in ISR,and that the SA-mediated response pathway was involved in the induction of ISR by strain A21-4 in pepper.6.The content of endogenous salicylid acid on pepper was researched by high performance ion chromatography(HPIC).These results point to SA content increased significantly after treatment with A21-4,it reached peak at the 72 th hours with increased by 458.29%.These results strongly indicated that A21-4 induced pepper systemic resistant relying on SA signal transduction pathway. |
PDF Full Text Request