Isolation and screening of IAA-producing bacteria from glutinous sorghum leaves and its plant growth-promoting function

Glutinous sorghum is an important raw material for the production of Baijiu(Chinese liquor). During its growth process, glutinous sorghum requires a substantial amount of chemical fertilizers. As an environmentally friendly fertilizer, microbial agent has a great application prospect in future. The aim of this paper was to develop a growth promoting microbial agent for glutinous sorghum. In this study, the glutinous sorghum leaves were used as experimental materials to isolate and screen microbial strains with plant growth hormone indole acetic acid(IAA)production ability. Phylogenetic analysis was performed to determine the taxonomic status of these microbial strains based on the 16S rDNA conserved sequences. The effects of strains on glutinous sorghum seed germination were analyzed by soaking the seeds with bacterial suspension. The effects of strains on the sorghum seedlings growth were analyzed by pot experiment. The results were as follows:(1)Four microbial strains capable of producing IAA were isolated and screened from glutinous sorghum leaves, designated as HY1-1, HY1-2, HY1-3, and HY1-4. Among them, HY1-1 exhibited the highest IAA production per unit concentration which was 2.56 mol·L-1.(2)Bayesian inference tree analysis based on the 16S rDNA sequences revealed that all four strains belonged to Bacillus subtilis.(3)HY1-1, HY1-2, HY1-3, and HY1-4 could promote the glutinous sorghum seed germination rates. Compared to the control groups, the germination rates of glutinous sorghum seeds soaked in bacterial suspension significantly increased by 40.04% to 165.52%. Among them, HY1-1 demonstrated the most prominent promotion effect, with a germination rate increase of 165.52%.(4)HY1-1 strain was selected for a pot experiment. After 30 days of inoculation on the roots of glutinous sorghum seedlings, the plant heights of the seedlings significantly increased by 29.17%, and total phosphorus content increased significantly by 5.12%. The rhizosphere substrate of glutinous sorghum exhibited a significant increase in available nitrogen content by 31.70% and available phosphorus content by 28.88%. In conclusion, HY1-1, an endophytic bacterium in glutinous sorghum leaves, can promote the growth of glutinous sorghum plants by secreting the plant growth hormone IAA and providing necessary nutrients. This study provides genetic resources for the further development of microbial agent targeting the growth promotion of glutinous sorghum.