Screening Of Plant Growth-Promoting Bacteria And Its Application In Promoting Rice Growth Under Saline-Alkali Stress

The food crisis has become a major concern of all countries.However,with the continuous changes of the global climate and the emergence of extreme climate,the growth and yield of rice have been greatly reduced due to various stresses,and the salt-alkali stress caused by soil salinization is more serious.At present,the way to improve rice growth and yield is mainly through the use of chemical fertilizers and pesticides,but it has many shortcomings,such as greater harm and unsustainable effects.These shortcomings can be compensated for by bio-fertilizers that are non-polluting,long-acting,and low-cost.The development and utilization of microbial fertilizers to increase yield and alleviate stress has received increasing interest in various countries,and the key issue is to develop growth-promoting bacteria with high efficiency.The aim of this work is to obtain efficient plant rhizosphere-promoting bacteria with phosphorus,nitrogen fixation,acetoacetate,siderphore,and 1-aminocyclopropane-1-carboxylic acid deaminase activity.36 strains with these growth-promoting properties were isolated from the soil.By comparing the growth-promoting properties,one strain outside the root and one strain in the root were screened out,and two strains with strong growth-promoting ability were selected and named as D1 and D2,respectively.The results showed that the effect of phosphate dissolving and siderphore production by strain D1 was significantly higher than that of D2(p<0.05).When the concentration of L-Trp in the medium increased,the amount of IAA synthesis also increased,and the amount of D2 synthesized was always significantly higher than that of D1(p<0.05).In the medium with 1.5 M NaCl,D1 showed a higher salt tolerance than D2,while in the medium of pH 10,the alkali resistance of D2 was better than that of Dl.Using 16S rDNA sequence analysis,strain D1 and D2 were identified as were Pantoea sp.and Enterobacter sp.,respectively.The growth-promoting abilities of the strain Dl and D2 were further verified by seed germination and pot experiments.The results showed that after inoculation of these two strains,the germination rate,germination potential,dry weight,plant height and root length of rice seedlings were significantly increased under stress or non-stress(p<0.05).The chlorophyll content,soluble protein content,free proline content and potassium and phosphorus content in the leaves of the seedlings were significantly increased,and the malondialdehyde,Na+content and Na+/K+were significantly lower than the uninoculated seedlings.In the absence of stress,the activities of antioxidant enzymes such as superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)were significantly enhanced,which reduced the accumulation of reactive oxygen species in seedlings and promoted growth.Under salt-alkali stress,the activity of each antioxidant enzyme was significantly lower than that of the uninoculated strain,which proved that the salt-alkali stress was effectively alleviated after inoculation.In this study,two strains with good salt and alkali resistance were screened,which could be tised as the preferred strain to alleviate the growth of rice under saline-alkali stress,which laid a foundation for the application of rhizosphere-promoting bacteria in biological fertilizer.