Study On Microecological Mechanism Of Rhodopseudomonas Palustris PSB-06 On Control Of Pepper Phytophthora Blight

Pepper Phytophthora blight is an important soil-borne disease in pepper production.The disease leads to pepper organ decays or whole plant perish.Pepper yield can be severely reduced or even crop failure.In practice,there are no permanent corresponding resistant varieties,and pepper Phytophthora blight control relies on comprehensive control,among which eco-friendly biocontrol agents or bioactive compounds are the promising way to achieve green control of this disease.In the continuous cropping pepper fields,previous studies showed that Rhodopseudomonas palustris PSB-06 exhibited 45.80% control effect on this disease.However,it is not clear whether PSB-06 preformed successfully to control pepper phytophthora blight through micro-ecological regulation.Based on our previous results,to make clear the control mechanism of PSB-06 on pepper Phytophthora blight,the eco-control effect of PSB-06 on the pepper Phytophthora blight in different growth stages in the field,and seedling stage in the greenhouse were investigated.The dynamic change on the physical and chemical properties,enzyme activities,bacteria and fungi communities in rhizosphere soil were also studied after PSB-06 treatment.The co-occurrence network mode of rhizosphere bacteria and fungi communities under different treatments was analyzed,and the effect of PSB-06 on regulating the rhizosphere process and microecological mechanism of pepper Phytophthora blight was determined.The results would provide new solutions for ecological control of pepper Phytophthora blight.The main results are as follows:1.Compared with the pepper only inoculated with Phytophthora capsici,the pepper co-inoculated with PSB-06 and P.capsici in seedling,flowering and fruit-setting,and fruiting stages in the field and in seedling stage in greenhouse showed the control effect of65.99%,75.99%,71.65% and 87.04%,respectively.These results showed that the PSB-06 had better control effect on pepper blight under different planting modes.2.Compared with the control,the activities of the enzymes(protease,nitrate reductase,phosphatase,urease)related to the conversion of nitrogen and phosphorus in rhizosphere soil in the field showed the trend of first decreased and then increased with the growth period of pepper.The tatalase showed the trend of first rose and then fell.In greenhouse,the soil catalase in the seedling stage was significantly decreased,while the nitrogen and organic matters content significantly increased.Under field and greenhouse conditions,it had no significant effect on total soil nutrients after PSB-06 inoculation.However,in certain growth periods,enzyme activities related to soil nutrient conversion and available nutrients content(alkali hydrolyzed nitrogen,available phosphorus and available potassium)were increased.It indicated that PSB-06 improved the state of soil nutrient supply,and provided good soil environmental conditions for enhancing host plants resistance to this disease as well.3.Compared with controland IPB inoculation,the bacterial α-diversity was significantly increased after PSB-06 inoculation.The impacts gradually decreased with the development of pepper plants.On the contrary,the bacterial α-diversity was significantly decreased after PSB-06 inoculation.Whether in the field or greenhouse,there was less effect on the rhizosphere fungi α-diversity than that of bacteria after PSB-06 treatment.In the field,the community structure of bacteria and fungi of rhizosphere soil during each growth stages were significantly changed by using PSB-06 treatment.However,the rhizosphere community structure of bacteria and fungi in the greenhouse did not show variation.In general,PSB-06 inoculation could increase the relative abundance of beneficial bacteria.Our results demonstrated that PSB-06 treatment had a certain regulatory effect on the composition and structure of the rhizosphere fungi and bacterial microbial community in each development stages of pepper.4.The eco-network relationship among species of microbial communities in pepper rhizosphere soil was analyzed.The results showed that,during the seedling and fruiting stages in the field and the seedling stage in the greenhouse,there were both positive relationships in bacterial network or fungal network.In the field,the average degree of bacteria and fungi network in the seedling stage were significantly increased,which indicated that PSB-06 treatment promoted the interaction of bacteria and fungi,and inhibited rapid expansion of P.capsici,and accompanied with the reduced occurrence of pepper Phytophthora blight.In the middle and late stages of pepper development,the interaction complexity of rhizosphere bacterial further increased,while the fungal interaction only changed slightly.In the greenhouse,PSB-06 inoculation had significant effect on the average degree of fungi network,while bacterial network did not.The results indicated that the interaction of fungi also affected the occurrence of diseases.Under field and greenhouse conditions,the network parameters of bacteria and fungi are mainly closely related to soil nitrogen conversion indexes(total nitrogen,protease,urease),indicating that soil nutrients are involved in the regulation of soil microbial interactions.5.Considering many soil factors including soil enzymatic activity,physical and chemical properties,rhizospheric microbial community,and rhizosphere bacteria and fungi community,the results showed that the disease index of pepper blight was closely related to catalase activity of rhizoshpere soil.Moreover,catalase activity as a driving factor affected the rhizosphere bacterial community,and was also one of the key factors driving the rhizosphere fungal community.The occurrence of pepper blight is closely related to rhizosphere soil catalase.Our results provided a new ecological control method for the prevention and control of Phytophthora capsica.This is the most important finding of our study.The pepper blight disease index is positively and negatively correlated with numerous bacterial and fungal species,but the related microbial populations in different periods are inconsistent.This indicates that the micro-ecological control of PSB-06 on pepper blight is complex,and with the help of the high-throughput sequencing,the analyzed microbial species related to the pepper blight can provide valuable information for the isolation and selection of the antagonistic bacteria against pepper Phytophthora blight in future.