Diversity and function of culturable rhizospheric bacteria of flue-cured tobacco K326 intercropped with five spice plants

Abstract:

[Background] Flue-cured tobacco is an important economic crop in China. Intercropping affects the diversity of rhizospheric microorganisms and alleviates the production of flue-cured tobacco. Rhizospheric microorganisms can adapt to changes in the rhizosphere microenvironment, which promotes the growth of flue-cured tobacco. [Objective] We examined the diversity of the bacterial population in flue-cured tobacco’s rhizosphere soil under the intercropping models between tobacco K326 and five spice plants at different growth periods. In addition, we compared the variances in intercropping models in various growing periods from the perspective of biological diversity and subsequently screened the adaptability and functional characteristic of typical rhizosphere bacterium. [Methods] Soil samples from various growing periods with different intercropping patterns were collected. We designed the culturing method to isolate and sequence the 16S rRNA gene, and calculated the diversity index. Representative strains were selected to detect nicotine and Cr2+ tolerance as well as growth-promoting properties. [Results] A total of 707 bacterial strains distributed in 70 genera were isolated. The change of the Shannon index of bacteria in flue-cured tobacco’s rhizosphere soil at the stem elongation period was W (4.079 191 7)>2GAY (3.840 352 1)>2GDY (3.514 562 8)>2GCKY (3.497 703 4)>2GBY (3.447 478 9)>2GCY (3.253 409 2)>2GEY (3.241 103 4). The change of Shannon index of bacteria in flue-cured tobaccos’ rhizosphere soil at the leaf ripening period was 3GAY (3.688 981 7)>3GCKY (3.442 125 1)>3GBY (3.353 155 8)>3GDY (3.349 171 9)>3GEY (3.306 294 5)>3GCY (3.305 582 2). The change of Shannon index of bacteria in flue-cured tobacco’s rhizosphere soil at the harvesting period was 5GEY (2.857 102 8)>5GBY (2.458 311 3)>5GAY (2.271 868 5)>5GCKY (2.210 253 6)>5GCY (2.079 441 5)>5GDY (0.693 147 2). The genera Arthrobacter, Bacillus, Brevibacillus, Brevendimononas, Microbacterium, Nocardioides, Pseudomonas, Rhodococcus, Streptomyces and Terrabacter were detected at all the three growth periods. Majority of the representative strains exhibit positive activities for nicotine tolerance, Cr2+ tolerance, nitrogen fixation, siderophore production, phosphorus solubilization and starch hydrolysis. [Conclusion] Rhizosphere soil contained abundant bacterial resources under the intercropping mode between five spice plants and the flue-cured tobacco K326. Among the dominant bacterial groups in flue-cured tobacco’s rhizosphere soil, the genera Bacillus, Pseudomonas and Streptomyces have potential applicability in nicotine tolerance, Cr2+ tolerance and growth-promoting effects. The intercropping can change the diversity of bacteria in rhizosphere soil of flue-cured tobacco. In the tobacco leaf ripening period, the intercropping of five spice plants and flue-cured tobacco significantly increased the diversity of cultivable bacteria in the rhizosphere soil. The intercropping types of Monarda didyma, Cymbopogon citratus and Pelargonium graveolens own advantages in relieving continuous cropping of flue-cured tobacco.