Isolation And Identification Endophyte From Switchgrass And Evaluate Their Promteeffects On Its Maternal Growth Under Salt Stress

Switchgrass(Panicum virgatum L.) is a perennial C4 plant with high potential as a bioenergy source. In order not to compete with food crop, most switchgrass should be grown on marginal land. However, switchgrass usually suffering from salt stress on marginal land. In order to improve the salt resistance of switchgrass, we isolated and identified PGPB(Plant growth bacterial) from switchgrass rhizome, and measured the ACC(1-aminocyclopropane-1-carboxylate synthase) deaminase and IAA activity of isolated bacteria. Then we evaluated their promote effects on switchgrass seed germination under NaCl salt stress. After that we selected one species of PGPB which contain ACC deaminase activity, and used an orthogonal matrix experimental design with four factors(bacterial liquid concentration, bacterial liquid treatment time, nitrogen content and NaCl) to quantitatively investigate the effects and pairwise interactions on the seedling growth(especially root development) using algorithmic modeling analyses. Then, we optimized the inoculation bacterial concentration, treatment time, salinity and nitrogen concentration for the seedling growth. We found that:1) Two bacterial species Pseudomonas sp.(P), Rhizobium sp.(R) were isolated, the ACC deaminase and IAA production activity of Pseudomonas sp. were 895±35(nmol α-ketobutyrate per mg protein per h) and 22.5±1.6 μg mL-1, respectively. However, Rhizobium sp. did not show any ACC deaminase activity, while its IAA production activity was 11.3±μg mL-12) P, R and their mixed bacteria(P+R) could promote switchgrass germination by increasing the germination rate, germination potential and germination index of switchgrass seeds, the radicle length, plumule length and reducing relative electrical conductivity of switchgrass seedling under salt stress. Hence, PGPR(P, R, and P+R) can promote switchgrass seed germination under NaCl salt stress and increase resistance of swithgrass seed to salt stress.3) The results showed that P significantly increased the total root length, root surface, shoot length, and fresh and dry weight through an effective proliferation of the number of first-order lateral roots and second-order lateral roots of the switchgrass cv. Blackwell. The bacterial increased the chlorophyll content and decreased soluble sugar and proline content indicated that P could attenuate salinity stress and improve switchgrass growth.4) Under NaCl salt stress, the optimal bacterial concentration, treatment time and nitrogen content was 0.5- 1.25 OD at 600 nm, 3 h, 60- 125 m M and 158 mg L-1, respectively.