Abstract:[Background] Plant growth-promoting rhizobacteria can accelerate nutrient cycling in the soil and improve the structure of soil microbial communities to enhance soil fertility. [Objective] To reveal the diversity of drought-tolerant actinomycetes in the rhizosphere of maize in Panxi Plateau, China and screen out plant growth-promoting drought-tolerant actinomycetes. [Methods] Drought-tolerant actinomycetes were isolated and screened from the rhizosphere soil of maize in the field with tobacco-maize rotation in Panxi Plateau, China. BOXA1R cluster analysis was performed to assess the diversity of drought-tolerant actinomycetes, and 16S rRNA gene sequencing was employed to determine their phylogenetic positions. The abilities of the isolates to produce ACC deaminase and siderophores, degrade cellulose, solubilize phosphorus, and inhibit pathogens were evaluated. The drought-tolerant strains capable of efficiently promoting plant growth were selected for drought stress experiments on maize seedlings. [Results] A total of 31 strains of drought-tolerant actinomycetes were isolated and identified. BOXA1R cluster analysis revealed that these strains belonged to Streptomyces, Nocardioides, Tsukamurella, Gordonia, and Amycolatopsis, among which Streptomyces was the dominant genus. Among the 31 isolates, 25.80%, 32.25%, 9.68%, and 74.19% could produce siderophores, solubilize phosphorus, degrade cellulose, and produce ACC deaminase, respectively. Strains SICAU-37 and SICAU-70 exhibited inhibitory effects on the pathogenic fungi Magnaporthe oryzae, Phytophthora nicotianae, and Cercospora zeina, with the ratios of the inhibitory zone diameter to the colony diameter being greater than 2 against all the three fungal species. Notably, strains SICAU-37 and SICAU-70 with prominent plant growth-promoting and antifungal properties were selected for drought stress experiments. Upon identification, these two strains were determined to be Tsukamurella tyrosinosolvens and Amycolatopsis dendrobii, respectively. Under drought conditions, SICAU-70 effectively promoted the growth of maize seedlings, increasing the plant height and fresh shoot weight by 9.44% and 33.42%, respectively. [Conclusion] The fields with tobacco-maize rotation in Panxi Plateau harbor diverse and rich plant growth-promoting drought-tolerant actinomycetes, which have application potential.
