| Understanding the mechanism of plant disease resistance can benefit the development of approaches for disease management.Root exudates are the chemical media of the "rhizosphere dia logue" between plants and pathogens,and play important roles in the response of plants to pathogen infection.Deciphering the complex network of plant-pathogen interaction mediated by root exudates can not only raise the awareness of the role of root exudates in plant disease resistance,but also contribute to the discovery of new strategies and technologies for disease control.Based on tobacco(Nicotiana tabacum)-Phytopthora nicotianae(pathogen of black shank)interaction system,the differences of bioactiviry,chemical composition and microecological effect of root exudates between resistant cultivar cv Gexin 3 and susceptible cultivar Xiaohuangjin1025 were compared.1.The root exudates of resistant and susceptible cultivars had distinct effects on P.nicotianae.The results of in vitro and in vivo bioassay showed that the root exudates of cv Gexin3 inhibited the mycelial growth and zoospore germination of P.nicotianae significantly,and reduced the disease severity,while that of Xiaohangjin 1025 had no significant effect on the mycelia l growth and zoospore germination,and increased the severity of black shank.2.Metabolic profiling using LC-MS,GC-MS and SPME GC-MS suggested different metabolic patterns of root exudates between resistant and susceptible cultivars.Tobacco roots exuded some disease related chemicals inc luding tartaric acid,ferulic acid,lauric acid,eugenol,guaiacol and other pote ntial substances,and released a variety of signal molecules for plant disease resistance such as salicylic acid,prohydrojasmon,unsaturated fatty acid,and 6-hydroxyhexanoic acid.Compared with the susceptible cultivar,the resistant cultivar secreted larger mumber and greater quantity of disease resistance related substances.Among the descriminant compounds identified,eugenol,2-ethylhexyl phtha late,tartaric acid,ferulic acid,4-tert-butylphenol,and lauric acid exhibited strong inhibition effect on P.nicotianae.Salicylic acid,eugenol,ferulic acid and lauric acid suppressed black shank disease significantly and were thought potentially useful in controlling the disease.3.The rhizospheric micro-ecological characteristics differed between resistant and susceptible cultivars.Compared with susceptible cultivar,the resistant cultivar harbored higher content of available phosphorus,higher saccharase activity,more species of culturable fungi,but fewer species of bacteria and actinomycetes in rhizosphere.Biolog-Eco microplate assay indicated that higher capacity of phenolic acid carbon substrate utilization was observed in the rhizhospheric soil of Gexin 3 plants.4.As the results of high-throughput sequencing of the V3-V4 region of 16 S rRNA and funga l ITS1 region,the rhizospheric microbia l community showed similar diversity but distinct structure between the rhizospheric soil of resistant and susceptible cultivars plants.Sphingomonas,Jatrophihabitans,Penicillium and Melaniospora were dominant in rhizospheric soil of resistant cultivar plants,while Massilia,Cladosporium and Mucor were abundant in susceptible cultivar.The diversity and richness of rhizosphere soil fungi were significantly increased by the rotationa l cropping of the resistant and susceptible cultivars;meanwhile,Sphingomonas,Jatrophiabitans,Streptomyces,Gemmatimonas,Devosia,Pseudoalbrys and Pseudogymnoascus were enriched in the rhizospheric soil of rotational cropping.5.The integrated comparision between the resistant and susceptible cultivars suggest that root exudates of resistant plants can provide direct and indirect defence mechanisms through a complicated network.And pathogen inhibition,elic iting systemic resistance,shifting the rhizosphere microbial community and promotion of soil nutrient releasing may play important roles in tobacco defense responses. |
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