Effects Of Drought Stress On The Composition And Structure Of Endophytic Bacteria Communities In Potato And Rhizosphere Soil

Drought stress is one of the most important problems facing crop production worldwide.In addition to traditional plant breeding and biotechnology such as genetic engineering,the role of endophytic bacteria and inter-root microorganisms in plant tissues in coping with drought stress has received much attention,but the role of endophytic bacteria and inter-root microorganisms in regulating plant drought stress in potato leaves is still unclear.In this study,we used Potato 6 as the material,and analysed the structural characteristics of potato leaf endophytic bacteria and inter-root soil bacterial communities under drought stress by traditional isolation and Illumina Novaseq sequencing,and screened for drought-tolerant and probiotic strains by measuring the metabolic activity of the strains and their ability to survive under low water potential.The PEG6000 was used to simulate drought stress,to verify and evaluate the growth-promoting effect of the screened endophytic strains on potato under drought stress,and to obtain endophytic strains that mitigate drought stress.The main results were as follows:Effect of drought stress on the composition and structure of endophytic bacteria in potato leaves.Drought stress did not affect the composition of potato endophytic bacteria at the phylum level,but drought stress increased the relative abundance of bacteria at the phylum level.The dominant phylum of endophytic bacteria in potato leaves was Amoebacteria,Thickwalls,Bacillariophyta and Actinomycetes during the whole period of potato fertility,in which the abundance of bacterial communities of Thickwalls increased by 637.00%,36.10% and 6.11% at the tuber formation,starch accumulation and maturity stages,respectively,compared with the control.The relative abundance of the bacterial communities of the phylum Aspergillus and the phylum Aphanizomenon increased by 19.21%,564.97% and 23.15%,654.50%at the seedling and tuber formation stages,respectively,and decreased by 24.76%,70.25% and 45.93%,16.30% at the starch accumulation and maturity stages,respectively,compared with the control;the relative abundance of the bacterial communities of the phylum Aspergillus decreased by 9.59%,57.14% and 7.13% at the seedling,tuber formation and maturity stages,respectively,compared with the control.The results of the Alpha diversity analysis showed that drought stress significantly increased the concentration and diversity of dominant species in the endophytic bacterial community of potato tuber-forming leaves,and the species richness of the endophytic bacterial community showed that drought stress significantly promoted the species composition of the endophytic bacterial community of potato leaves at the tuber formation > seedling > maturity > starch accumulation,while the number of species in the endophytic bacterial community of potato leaves at the seedling > maturity > starch accumulation stage under normal conditions was in descending order.Under normal conditions,the number of species in the endophytic bacterial community of potato leaves under drought stress was in the order of tuber formation > seedling > maturity >starch accumulation,while under normal conditions it was seedling > tuber formation >maturity > starch accumulation.Effects of drought stress on the composition and structure of bacterial communities in potato rhizosphere soil.Drought stress did not affect the bacterial composition of potato rhizosphere soil at the gate level,but drought stress increased the relative abundance of bacteria at the gate level.Under drought stress and normal watering treatment,the relative abundance of Proteobacteria,Acidobacteria,Actinomycetes,Budomonas,Campylobacter,Bacteroides,and Myxococcus in the rhizosphere soil of potato during the entire growth period is not affected by drought stress,Other dominant bacteria are all affected by drought stress.Compared with normal irrigation(CK),the relative abundance of Proteobacteria decreased during the entire growth period of potatoes compared to the control,with a decrease of 24.79% in both seedling and mature stages;The relative abundance of Acidobacillus decreased by9.29% during starch accumulation,but increased by 0.83%,12.49%,and 70.79%during seedling,tuber formation,and mature stages,respectively;The relative abundance of actinomycetes increased throughout the entire growth period of potatoes,with an increase of 117.75%,7.52%,184.25%,and 4.13% in seedling,tuber formation,starch accumulation,and mature stages,respectively.RDA and Mantel tests showed that soil electrical conductivity and p H were key factors affecting bacterial community composition in potato rhizosphere soil under normal irrigation and drought stress.In addition,organic carbon also significantly affects the composition of bacterial communities in the rhizosphere of potato under drought stress.Alpha diversity analysis showed that drought stress would not affect the richness and concentration of dominant species of rhizosphere bacterial communities during the entire growth period of potatoes,but would increase the number of rare species and change the richness and uniformity.Isolation,Identification and function of endophytic bacteria relieving drought stress in potatoes.Both Pseudomonas stutzeri(ML-D6,Ps)and Bacillus thuringiensis(ML-D18,Bt)strains have IAA and ACC deaminase production activities,and Bt strain has phosphorus solubilization ability,while Ps strain has nitrogen fixation ability.Under drought stress,inoculation with Ps and Bt had significant growth promoting effects on potatoes.Compared with the control,the root length of potato plants increased slightly but not significantly.After inoculation with Bt,the plant height and stem diameter increased by 16.7% and 16.0%,respectively,compared to the control under severe drought stress;Under moderate drought stress,after inoculation with Ps and Bt,the relative chlorophyll content of potato leaves increased by 11.6% and 11.1%,and the stomatal conductance increased by 26.5% and 11.2%,respectively,compared to the control.Under severe drought stress,the net light and rate of plants inoculated with Ps and Bt increased by 33.7% and 34.3%,respectively,compared to the control;After inoculation with Ps and Bt,the proline content in potato plants under moderate and severe drought stress increased by 49.7%,70.9%,and 24.8%,25.2%,respectively,compared to the control,and the proline increment after inoculation with Ps was significantly higher than that after inoculation with Bt under the same treatment;Under moderate drought stress,the soluble protein concentration of potato plants inoculated with Bt increased by 33.0% compared to the control,while the soluble protein concentration of potato plants inoculated with Ps decreased by 14.8% compared to the control;Under moderate and severe drought stress,the content of malondialdehyde significantly decreased after inoculation with Ps and Bt compared with the control;After inoculation with Ps,the activities of CAT and SOD increased by 42.4% and 64.3%,57.4% and 25.0%,respectively,compared to the control under moderate and severe drought stress;After inoculation with Bt,POD activity increased by 26.5% compared to the control under moderate drought stress,and SOD activity increased by 57.9% and35.1% compared to the control under moderate and severe drought stress,respectively.Inoculating potato endophytic bacteria Bt and Ps can alleviate the drought resistance of potatoes,and under severe drought stress,Bt strain is superior to Ps strain in alleviating drought stress in potatoes,while Ps strain is superior to Bt strain in alleviating drought stress in potatoes under moderate drought stress.