Screening And Identification Of Rhizosphere Growth Promoting Bacteria Of Dongxiang Wild Rice And Its Effect On Rice Growth And Drought Tolerance

In this paper,directed-enrichment screen method was used to isolate and screen two growth promoting bacteria with ACC(1-aminocyclopropane-1-carboxylie acid)deaminase activity from the rhizosphere soil of Dongxiang Wild Rice,a unique and characteristic plant in Jiangxi Province,and the two strains were identified by means of physiological,biochemical and molecular biology.Rice 9311 was used as the research material.The growth promoting effect of strains on rice was investigated under normal water.The impact on rice inculated strains was detected under natural drought stress.The results were as follows:1.After enrichment cultivation and screening with a unique nitrogen source,two rhizosphere growth-promoting bacteria with high ACC deaminase activity were isolated from the rhizosphere soil of Dongxiang Wild Rice and they were named A5and A18 respectively.At the same time their specific activities of deaminase were0.1214U/mg and 0.0671U/mg.It was found that both strains could produce IAA(Indole Acetic Acid),had better abilities to dissolve inorganic phosphorus and produce HCN(Hydrogen cyanide).The IAA production ability of strain A5 was higher than that of A18 and the inorganic phosphorus production ability of A18 was higher than that of A5.However,the iron carrier capacity of both was weak.According to the measurements results of bacterial morphology,physiological and biochemical indexes,combined with the phylogenetic analysis of 16S rDNA sequence,strains A5 and A18 were finally identified as Pseudomonas vancouverensis and Pantoea cypripedii.2.The germinated rice seeds were soaked with bacterial suspensions A5,A18,A5+A18,and the relevant indicators were measured 40 days later after emergence.The results showed that compared with non-inoculated group(control group),morphology indexes such as plant height,leaf width,aboveground and belowground fresh weight and physiological indexes including chlorophyll,soluble protein,photosynthetic rate,stomatal conductance,intercellular carbon dioxide and transpiration rate of rice inoculated strains A5,A18,A5+A18 improved greatly.The plant height increased by 42.22%,33.96%,30.92%;fresh weight of the underground part increased by 194.60%,192.89%,182.05%;fresh weight of the upper part of the ground increased by 83.95%,67.06%,74.46%and total fresh weight increased by98.98%,84.15%,89.07%;the leaf width increased by 62.45%,61.82%,58.60%;the content of chlorophyll a increased by 23.20%,23.25%,22.65%;chlorophyll b content increased by 105.57%,94.37%,59.43%;total hlorophyll content increased by 50.76%,47.04%,34.95%;soluble protein content increased by 26.88%,57.96%,46.24%;net photosynthetic rate increased by 22.33%,25.09%,19.37%;the stomatal conductance increased by 68.56%,95.62%,51.77%;intercellular carbon dioxide concentration increased by 43.15%,63.82%,40.05%and transpiration rate increased by 69.46%,81.59%,41.42%.It could be concluded that strains A5 and A18 have a very good growth promoting effect on rice.3.The germinated rice seeds were soaked with bacterial suspensions A5,A18,A5+A18,watered normally in the early stage,and treated with natural drought 40days after emergence.The physiological indicators were measured on the day before drought and the first,second,third and fourth days of drought stress.The results showed that the net photosynthetic rate(P_n),stomatal conductance(G_s),and transpiration rate(T_r)of leaves of rice inoculated strains A5,A18,A5+A18 increased significantly and reduced the magnitude of decline under drought stress,compared with non-inoculated rice.In addition,the inoculated strains A5,A18,A5+A18contributed to the accumulation of soluble protein,proline and total soluble sugar in rice leaves,and reached the maximum value on the third day under drought stress.The content of soluble protein was 1.53,1.17,1.33 times of those non-inoculated rice.The proline content was 1.84,1.09,1.34 times of those non-inoculated rice.and the content of total soluble sugar was 1.70,1.21,1.27 times of those non-inoculated rice.The above analysis showed that the inolulation of strains A5,A18,A5+A18 could improve the photosynthetic capacity of rice leaves and promote the accumulation of osmotic adjustment substances of rice to cope with drought stress.Among them,the inoculation effect of strain A5 was remarkable.