Colonization Process Of Arbuscular Mycorrhizal Fungi And Their Biological Control Of Pepper Phytophthora Blight

Arbuscular Mycorrhizae Fungi（AMF）are mutual symbionts of most terrestrial plants.It has been well accepted that AMFs play key roles in enhancing the nutrient caputure and stress tolerance of their hosts.In recent years,some AMF taxa were 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.The arbuscular mycorrhizal colonization of pepper was firstly investigated in field under natural invasive conditions in this study.Meanwhile,we selected two AMF taxa of Funneliformis mosseae,which harbors MRE in the cytoplasm of its hyphae and spores,and Rhizophagus intraradices with no MRE in its cytoplasm as our experimental materials.The pot experiment was conducted to study the growth-promoting effect of AMF on pepper seedlings and colonization in host plants,as well as the effects of different AMFs on pepper growth and pepper phytophthora blight.The possible potential factors causing the differences were preliminarily discussed.We primarily investigated the colonization and symbiosis between AMF and pepper under natural conditions.The results showed that AMF colonization and their AM structures within pepper roots were discovered among different sample sites,and the colonization rate was above 70%.Meanwhile,there were abundant AMF spores in rhizosphere of pepper at different sites,with an average of 6 spores g^-1soil.The AMF colonization rate,colonization intensity and rhizospheric spore density were different among sample sites.With increasing the AMF colonization intensity,the AM abundance and rhizospheric spore density also increased.The symbiosis of MRE with AMF taxa was checked by molecular method.The results showed that Funneliformis mosseae harbored MRE of Candidatus Moeniiplasma glomeromycotorum in its spores,but Rhizophagus intraradices had no.The root samples of pepper were stained by the method of lactic acid glycerol staining,and the AMF colonization and their structures of arbuscular mycorrhizae（AM）in pepper roots were checked under the microscope.The results showed that two AMF taxa could be successfully colonized within pepper roots.AMF infects plants starting from germination of extracellular spores and then forms appressoria on the root surface,another case is that the extermal hyphae invade the root cortex cells of the pepper directly,forming some stuctures such as intercellular hyphae,intmcellular hyphae,arbuscules and vesicles.The effects of two AMF taxa on pepper growth and their biocontrol of pepper phytophthora blight were studied under pot experimental conditions.The results showed that two AMF taxa could infect the pepper roots,but the infection rate was different.The infection rate of Funneliformis mosseae was significantly higher than that of Rhizophagus intraradices.Compared with the control,the plant height,stem diamete,fresh weight and dry weight of the peppers with inoculations of Funneliformis mosseae and Rhizophagus intraradices were higher than those of the control treatment.The plant height of peppers increased by 9.36%and 6.24%,the stem diameter increased by9.09%and 4.55%,the fresh weight increased by 40.36%and 32.74%,and the dry weight increased by 63.16%and 31.58%.With challenging inoculation of Phytophthora capsici for peppers,the plant height,stem diamete,fresh weight and dry weight of peppers colonized by Funneliformis mosseae and Rhizophagus intraradices in their roots were higher than those of the control treatments of the special inoculation of Phytophthora capsici.The plant height increased by 6.50%and 2.99%,the stem diameter increased by 10.53%,the fresh weight increased by32.64%and 31.25%,and the dry weight increased by 35.71%and28.57%.These results showed that AMF could promote the plant growth of pepper.Two AMF taxa could control the pepper phytophthora blight.The control efficiency of Rhizophagus intraradices against pepper blight was 54%,while that of Funneliformis mossea was only 8.3%.Different AMF taxa had different bioconrtrol efficiency against pepper blight.The results indicated that AMF could establish the stable symbiotic relationship with pepper and effectively promote the growth of pepper plants.AMF had a certain biocontrol effect on pepper blight,but different AMF taxa had different effects on the growth of pepper and the biocontrol of pepper blight.This study will provide scientific basis and technical support for the application of AMF in pepper production and control of pepper blight,and to a certain extent can help people to predict and evaluate the role of AMF.