Growth-promoting Effect And Resistance To Disease Stress Of Endofungal Bacteria To Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhizal fungi(AMF,Glomeromycotina)are widely distributed in nature,and they are one kind of obligate biotrophs mutually colonizing roots of most terrestrial plants.Studies have found that different AMF taxa do not have significant consistent effects of the benefits on plant hosts,and these host AMFs have been found that they harbored obligate mycoplasma-related endobacteria(MRE)in the cytoplasm of their hyphae and spores,but the others did not harbor any MRE.They play the important roles in promoting host plant growth and development,stress tolerance and their disease resistances.In this study,we choosed Rhizophagus clarus(Rc)、Funneliformis mosseae(Fm)and Claroideoglomus etunicatum(Ce)with MRE,and Rhizophagus intraradices(Ri)without MRE as experimental materials,and morphological and molecular identifications of AMFs and MRE were conducted.We build the symbiotic interaction between different AMF taxa and their host peppers.The growth indicators of mycorrhizal infection rate,plant height,fresh and dry weight of pepper,as well as physiological indicators of chlorophyll content,colonization rate,chitinase and phenylanlanine ammonia lyase(PAL)activity and their pepper blight control rates against Phytophthora capsica(Pc)were measured.On the basis of the results above,we explored the potential influence factors of MRE on the growth and the defense against pepper blight among the interaction system of the host AMF and pepper plants.The results are as follows:(1)Under the potted condition,compared with CK,R.clarus(Rc)had the most significant effect on the growth promoting of pepper plant height,increasing by33.4%;R.intraradices(Ri)had the most significant effect on the growth of stem diameter,increasing by 28.2%;F.mosseae(Fm)had the most significant effect on fresh and dry weight with increasing by 119.8% and 159.7% respectively.Clearly,Fm with MRE had a significantly higher growth-promoting effect on the various components of pepper plants than those of Ri,but the growth-promoting effect of stem diameter is lower than that of Ri.Different AMFs had obvious differences in growth promoting for their host plants.Compared with CK,Rc,Fm and Ce with MRE increased the chlorophyll content of the host plants significantly by 48.8%,46.1% and39.53% respectively.Ri had not significant difference from which those are without MRE in chlorophyll content.(2)The different AMF taxa have different ways to infect roots of host plants.Four AMFs can colonize in pepper root tissues by producing hyphae,vesicles and arbuscular structures.Ri with MRE germinated and form appressorium on the root epidermis,then mycelium invaded the root epidermis through the invasion point of appressorium,but Fm,Rc and Ce with MRE invaded the root epidermis directly through the invasion point after the hyphae germinated from the spores.At the same time,Fm colonization rate is 85.8%,it is significantly higher than the colonization rate of Ri in roots without MRE.In addition,the colonization rate of Rc and Ce are33.65% and 62.84%,there are not significantly different from the colonization rate of Ri.(3)Through morphology combining with the molecular phylogeny of Large-subunit(LSU)28S to identify four AMFs,the results showed that four AMFs were Rc,Fm,Ce and Ri.Ri does not harbor MRE,but Fm,Ce and Rc have symbiosis with MRE through molecular test of Small-subunit(SSU)16S.(4)Under the potted condition,established symbiosis with four kinds of AMF and inoculated Phytophthora capsica(Pc)in pepper plants.The results showed that the control effect of Fm was 22.7%,Rc was 33.6%,Ce was 22.7%,which those are with MRE,but Ri without MRE was 48.5%,Fm,Rc and Ce chitinase compared with single inoculation of Pc,the four AMFs all promoted the host plant to increase the activity of the above two enzymes to reduce the disease stress.This study showed that MRE had potential roles and influences mediated by its host AMF on ecological function of growth-promoting and disease-resistance of symbiotic plants,which revealed an important foundation for the role of MRE in the mutually beneficial symbiosis between AMF and host plants.The results provide theoretical basis for the application of AMF in agricultural practice,and contribute to the understanding of development and utilization for resources of AMF to some extent.