Genetic diversity,stress resistance,and effect on rice seedling growth of indoleacetic acid-producing endophytic bacteria isolated from Aconitum carmichaelii Debeaux

Abstract:

[Objective] To explore the genetic diversity,phosphorus- and potassium-solubilizing ability,stress resistance,and effect on rice seedling growth of indoleacetic acid (IAA)-producing endophytic bacteria isolated from Aconitum carmichaelii Debeaux and to provide scientific support for the sustainable development of A.carmichaelii industry.[Methods]Culturable endophytic bacteria were isolated from surface sterilized healthy plants of A.carmichaelii,and their IAA-producing capacities were measured by Salkowski spectrophotometry.The genetic diversity and phylogenetic status of these bacteria were studied via 16S rDNA-restriction fragment length polymorphism (16S rDNA-RFLP) and 16S rDNA full-length sequence.The phosphorus- and potassium-solubilizing abilities and stress resistance of them were studied by plate culture method.The effects of IAA-producing endophytic bacteria on the seed germination rate of rice were tested by semi-solid culture method after the seeds were immersed in bacterial liquids for 30 min.The effects of the endophytic bacteria on rice seedling growth were investigated by hydroponic experiment in our laboratory.[Results]Twenty-four endophytic bacterial strains were isolated from healthy A.carmichaelii,with the IAA-producing capacities ranging from 21.39 mg/L to 84.43 mg/L.The 16S rDNA-RFLP analysis indicated that these 24 strains were classified into 12 groups.The phylogenetic tree constructed based on 16S rRNA gene sequences showed that the representative strains belonged to Enterobacter,Klebsiella,Pantoea,Pseudomonas,Microbacterium,Bacillus,Sphingobacterium,and Chryseobacterium,which demonstrated high genetic diversity.Twelve strains showed strong potassium-solubilizing capacities.Most of the strains could grow normally within wide ranges of pH,temperature,and NaCl concentration,while they showed little resistance to different antibiotics.Ten strains significantly improved the germination rate of rice seeds,and 16 strains significantly promoted the growth of rice seedlings.We screened out 3 strains JY1-1S,JY3-6S,and JY10-1L that could not only improve the seed germination rate but also promote the seedling growth of rice.[Conclusion] A.carmichaelii harbored rich and diverse IAA-producing endophytic bacteria.We screened out 3 endophytic bacterial strains that could promote the seed germination and seedling growth of rice.This study laid a foundation for the development of plant growth-promoting biological fertilizer in the future.