Screening And Identification Of Endophytic Bacteria In Eco-friendly Salt-tolerant Gramineous Plants And Their Promotion Effect On Crops

Since plant endophytic bacteria live in plants during part or all of their life history,they have gradually formed a mutually beneficial relationship with plants in the process of co-evolution.This study attempts to screen out endogenous bacteria that are highly salt-tolerant,have a growth-promoting effect on major crops,increase the growth of crops under saline-alkaline conditions,and provide good strains for field application.In the study,74 endophytic bacteria were isolated and purified from the roots and stems of gramineous plants grown on saline-alkaline land.Among them,4 were endophytic bacteria that could be grown well at a concentration of 175 g/L sodium chloride,six strains on 200 g/L of chlorine.Furthermore,three phosphorus-solublizing strains,four strains with nitrogen-fixing,and 12 strains that could secrete IAA.Two different strains of endogenous bacteria GWG2 and LWG2 secreting higher IAA were used as follow-up research subjects.Through morphological observation,physiological and biochemical characteristics identification,16S rDNA sequencing and evolution analysis,GWG2 was identified as Bacillus and LWG2 as Acinetobacter.In this study,single factor optimization was used to optimize the fermentation conditions of endophytic bacteria GWG2 and LWG2.The results indicated that,the optimal culture condition for GWG2 was as follows:inoculation amount(4%),temperature(37?),initial pH(7.5).Liquid volume is 60mL.The glucose and peptone were the finest carbon and nitrogen sources,respectively.The best inorganic salt is dipotassium hydrogen phosphate.While in strain LWG2,the optimal culture conditions were as follows:inoculation amount 2%,temperature 37?,initial pH 7.0,Liquid volume is 40mL,and optimal source of carbon or nitrogen was the same.The best inorganic salt is magnesium chloride.In this experiment,the growth promoting effect of endophytic bacteria GWG2 and LWG2 on wheat seedlings under salt stress was studied.The results showed that the two endophytic bacteria had different promoting effects on wheat seedlings under the condition of 3%NaCl stress.Both endophytic bacteria had an increase in the germination rate of wheat seeds,and significant levels were found in germination potential,germination rate,germination index,and seed vigor index in the GWG2 treatment group at a concentration of 109.The effect of 109 treatment group was higher than that of 108 treatment group.The high promotion effect was higher than that of GWG2;among them,the strain LWG2 109-treated group had a greater promotion of seedling height which increased by 21%after 15 days of culture.