Effect Of Bacterial Synthetic Community On The Growth And Drought Resistance Of Astragalus

Astragalus membranaceus(Fisch.)Bge.var.mongholicus(Bge.)Hsiao is a kind of widely used herbal medicine in China,the yield and quality of artificial cultivation of Astragalus mongholicus Bunge is often reduced by drought stress,drought and water shortage is the bottleneck restricting the development of Astragalus mongholicus Bunge industry.In order to effectively improve the yield and quality of Astragalus mongholicus Bunge under the premise of reasonably saving and controlling agricultural water use,this study aims at Astragalus mongholicus Bunge root endogenous bacteria and inter-root microorganisms,screens out the promoting bacteria with the potential to promote growth and improve the quality of Astragalus mongholicus Bunge,and constructs a synthetic flora that can alleviate drought stress.The following results were achieved:1.123 strains of bacteria were isolated from the root and rhizosphere soil of Astragalus mongholicus Bunge treated with drought stress,identified from 35 genera,of which Pseudomonas(24.39%),Rhizobium(11.38%),Promicromonospora(5.69%),Streptomyces(5.69%),Nocardia(4.88%)accounted for a larger proportion.Based on the 123 strains of bacteria and the 306 strains of Astragalus root endophytes and rhizosphere bacteria preserved in the laboratory,68 strains of organophosphate-decomposing bacteria,97 strains of inorganic phosphorus-dissolving bacteria,63 potassium-dissolving bacteria,123 strains of indole-3-acetic acid producing bacteria,58 strains of ACC deaminase producing bacteria and 21 strains of siderophore-producing bacteria were qualitatively screened.Based on the qualitative results,25 multifunctional bacteria were selected.Among them,the available phosphorus content in the fermentation broth of HQB-9(Bacillus sp.)reached 624.40 mg/L,and the available phosphorus content in the fermentation broth of 9 organophosphate decomposing bacteria was0.67 ～ 4.40 mg/L.The potassium dissolution rate of 10 strains of potassium dissolving bacteria was 0.55% to 1.49%,and the enzyme activity of 15 strains of ACC deaminase was in the range of 0.21 to 11.23 μmol/(mg·h).The content of indole-3-acetic acid in fermentation broth of 20 strains of indole-3-acetic acid producing bacteria was in the range of 0.86 ～ 5.53 mg/L.2.25 strains of multifunctional bacteria were combined in a way of superimposing and synergizing functions,complementing functions,and giving priority to species with ecological adaptability,to construct 14 synthetic bacterial groups and complete 14 synthetic flora treatments and HQB-84,HQB-383 single inoculation treatment of Astragalus mongholicus Bunge for promoting growth test.The plant test found that the root length,plant height,root biomass,and above-ground biomass of the combination 6(including 15 strains)were significantly higher than those of the control group.Astragalus mongholicus Bunge showed strong roots and tall plants.The total content of Astragaloside IV and Calycosin-7-glucoside in each dry root of Astragalus mongholicus Bunge in the combination 6 were higher than those in the other treatment groups,which were 150.17% and 457.20% higher than those of the control group,respectively.Considering the growth index and the medicinal ingredient index comprehensively,it is found that the combination 6 has better growth-promoting performance than single inoculation bacteria and other synthetic bacteria groups.3.The effects of inoculation treatments of the combination 6,HQB-84 and HQB-383 on the growth of Astragalus mongholicus Bunge under different drought conditions were explored through plant experiments.Under mild,moderate,and severe drought stress,the growth indexes of Astragalus mongholicus Bunge in the combination 6 were higher than those of the control group,and the increase was the largest under moderate stress(except for root diameter),and the root dry weight was 84.62% higher than that of the control group.The total content of three flavonoids in each dry root of Astragalus mongholicus Bunge in the combination 6 reached the maximum under moderate stress,and the total content of Calycosin-7-glucoside was 228.09% higher than that of the control group,it can be seen that the growth-promoting properties of Astragalus mongholicus Bunge in the combination 6 are more significant under moderate drought stress.Compared with the two single inoculation treatments,the combination 6 has more significant growth-promoting properties on the roots of Astragalus mongholicus Bunge,while the single-inoculation group has more prominent growth-promoting properties on the above-ground parts of Astragalus.For the actual needs of using dried roots of Astragalus as medicine,the combination 6 is better.4.Under mild and moderate drought stress,the soluble protein content and proline content of leaves of the combination 6 were significantly higher than those of the control group and higher than the two single-inoculation treatments,the activities of superoxide dismutase,peroxidase and catalase in the combination 6 were significantly higher than those in the control group,the content of malondialdehyde in the combination 6 was lower than that in the control group and two single-inoculation treatments.It is found that the combination 6 has better growth-promoting and drought-resistant properties than single-inoculation treatments.