Abstract:

Plant growth-promoting rhizobacteria that are able to produce indole-3-acetic acid （IAA） are useful for the development of high-efficiency microbial fertilizers. In this study， IAA-producing rhizobacteria were isolated from the rhizosphere soil of Kalidium foliatum growing in the Kizilsu Kirgiz Autonomous Prefecture of Xinjiang by culturing on selection media. The isolates were identified on the basis of 16S rDNA PCR-restriction fragment length polymorphisms and their 16S rDNA gene sequences. The effects of strains with a strong ability to produce IAA on the germination of maize and wheat seeds were determined. Furthermore， their effects on the growth of maize and wheat seedlings （plant height， stem diameter， aboveground dry weight） under saline-alkali stress were verified in pot experiments. A total of 67 isolates were screened， and their IAA production capacity ranged from 16.65 to 71.63 mg·L^-1. Among all the strains， PM14 and PM18 showed the highest IAA production capacity. In addition， strains PM14 and PM18 were capable of phosphorus solubilization and nitrogen fixation. On the basis of 16S rDNA gene sequence and phylogenetic analyses， the isolates were divided into six genera， of which Enterobacter was the dominant genus. Both PM14 and PM18 promoted seed germination， but there were significant differences in the promoting effect on seed germination between low- and high-concentration groups （P<0.05）. After inoculation with PM14 or PM18， the plant height， fresh weight， aboveground dry weight， stem diameter， and root dry weight of maize seedlings were increased by 4.7%-37.2%， 28.8%-94.5%， 15.8%-157.9%， 4.4%-35.5%， and 23.5%-82.4%， respectively， but there was no significant effect on chlorophyll content. The plant height， stem diameter， fresh weight and aboveground dry weight of wheat seedlings were increased by 9.5%-33.1%， 13.0%- 49.6%， 57.4%-112.8%， and 71.4%-114.3%， respectively， after inoculation with PM14 or PM18. Except for an inactivated culture of PM14， all other treatments had positive effects on root dry weight， with increases ranging from 52.8% to 69.0%. However， none of the treatments significantly affected chlorophyll content. In summary， IAA-producing plant growth-promoting rhizobacteria improved the resistance of wheat and maize plants to salt-alkali stress， which is of great significance for the development of microbial fertilizers suitable for cultivating crops in salt- and alkali-affected areas.

Key words: indole-3-acetic acid （IAA）, plant growth-promoting rhizobacteria （PGPR）, saline-alkali stress, growth-promoting effects, microbial fertilizer