Identification of an endophytic Bt strain from potato and its alleviation to drought stress

【Objective】 To investigate the physiological response of the endophytic bacterium Bt in potato to alleviate host drought stress, and to provide a theoretical basis for the mechanism of endophytic bacterial drought stress alleviation and drought management in potato.【Method】 An endophytic strain of Bt isolated from potato leaves was identified by morphological and molecular sequencing methods, and the survival ability and metabolite activity of the strain were determined under low water potential;a pot experiment was conducted using PEG-6000 to simulate drought stress treatment, with drought treatments divided into normal watering(CK:PEG-6000 concentration of 0), moderate drought stress(D1:PEG-6000 concentration of 20%) and severe drought stress(D2:PEG-6000 concentration of 25%) were used to study the pro-growth effect and physiological response of inoculated Bt endophytic strain on potato under drought stress, and to evaluate their drought resistance.【Result】 Molecular identification of Bt as Bacillus thuringiensis of Bacillus, a strain with the ability to survive under low water potential, IAA-producing activity and ACC deaminase activity, showed that inoculation of Bt under drought stress had obvious effect on potato growth promotion. Compared with CK, the root length of potato plants increased but not significantly(P>0.05, the same below), plant height and stem thickness increased by 16.7% and 16.0% respectively under D2 treatment compared with CK;the relative chlorophyll content(SPAD value) and stomatal conductance of plant leaves increased by 11.1%, 20.5% and 11.2%, 77.8% respectively after Bt inoculation under D1 and D2 treatments compared with CK.The net photosynthetic rate of plants inoculated with Bt increased by 34.3% compared with CK under D2 treatment;the proline content in potato plants increased by 24.8% and 25.2% compared with CK under D1 and D2 treatments respectively, and the soluble protein content of potato plants increased by 33.0% compared with CK after inoculation with Bt under D1 treatment. In D1 and D2 treatments, malondialdehyde(MDA) content was significantly reduced by 37.1% and 14.9% compared to CK(P<0.05);CAT activity of plants inoculated with Bt under drought treatment increased but not significantly compared to CK, peroxidase(POD) activity increased by 26.4% compared to CK under D1 treatment, and superoxide dismutase(SOD) activity increased by 57.9% and 35.1% compared to CK under D1 and D2 treatments respectively. The drought resistance of potatoes under different treatments was evaluated comprehensively by the fuzzy mathematical affiliation function method, and the drought resistance was D2-Bt, CK-Bt, D1-Bt, D2-W, CK-W and D1-W in order.【Conclusion】 The potato endophytic bacterium Bt promotes potato growth and development by producing IAA and ACC deaminases to alleviate drought stress in potato.