The culturable microbial diversity in tobacco rhizosphere and their plant growth-promoting and biocontrol properties

Abstract:

[Background] Studies have shown that rhizosphere microorganisms play an important role in the root ecosystem, influencing the nutrient absorption and health of plant. [Objective] To understand the culturable microbial diversity in the rhizosphere of flue-cured tobacco variety K326 growing in four tobacco fields, which does not occur disease for many years, and to screen strains with the biocontrol and plant-growth promoting function for tobacco diseases control. [Methods] Traditional culture-dependent methods were used to isolate and identify bacteria and fungi in tobacco rhizosphere soil. The plant growth-promoting characteristics and pathogen antagonism of the strains were evaluated, and the growth-promoting effects of typical strains were further verified on tobacco seedlings. [Results] In this study, 261 isolates were obtained, including 160 bacterial strains and 101 fungal strains. Bacterial phyla of Proteobacteria and Firmicutes and fungal phyla of Ascomycota and Mucoromycota are the main groups. At the genus level, Pseudomonas and Bacillus were the most abundant genera in bacteria, and Aspergillus and Penicillium dominated in fungi. Next, 44 bacterial strains were selected from different species as representatives. We found that they all have IAA production ability, 9 strains can dissolve organic phosphorus, 16 strains can dissolve inorganic phosphorus, 13 strains produce siderophores, and 14 strains produce ACC deaminase. 25 and 26 strains that inhibiting the pathogens of bacterial wilt and black shank diseases were obtained from 160 bacterial strains, respectively. The pot experiment found that P. koreensis HCH2-3, P. lurida FGD5-2 and B. velezensis EM-1 can promote growth of tobacco seedlings, and consortium of these three strains has the most obvious growth-promoting effect. [Conclusion] There are numerous microorganisms with the potential to control disease and promote plant growth in the tobacco rhizosphere. Application of synthetic bacteria or functional complementary strains is an important direction for the development of microbial agents in the future.