Abstract
Endophytic bacteria (EB) are both a novel source of bioactive compounds that confer phytopathogen resistance and inducers of secondary metabolites in host plants. Twenty-seven EB isolated from various parts of Metasequoia glyptostroboides, Ginkgo biloba, Taxus brevifolia, Pinus densiflora, Salix babylonica, and S. chaenomeloides could produce salicylic acid (SA). The highest producers were isolates EB-44 and EB-47, identified as Pseudomonas tremae and Curtobacterium herbarum, respectively. Nicotiana benthamiana grown from EB-44-soaked seeds exhibited a 2.3-fold higher endogenous SA concentration and increased resistance against P. syringae pv. tabaci, the causative agent of tobacco wildfire disease, than plants grown from water-soaked seeds. N benthamiana and N. tabacum grown from EB-44-treated seeds developed 33% and 54% disease lesions, respectively, when infected with P. syringae pv. tabaci, and showed increased height and weight, in addition to 4.6 and 1.4-fold increases in nicotine accumulation, respectively. The results suggest that SA-producing EB-44 can successfully colonize Nicotiana spp., leading to increased endogenous SA production and resistance to tobacco wildfire disease. The newly isolated EB can offer an efficient and eco-friendly solution for controlling wildfire disease and nicotine accumulation in Nicotiana, with additional application for other important crops to increase both productivity and the generation of bioactive compounds.
Highlights
Endophytes comprise fungi or bacteria that colonize plant tissues without harming the host plant [1]
Seedlings of N. tabacum were transferred to the glasshouse for further experiments and N. benthamiana seedlings were grown under fluorescent light at 120 μE/(m2·s) under a 16/8 h light/dark photoperiod at 23 ◦C in a walk-in chamber
To test whether the salicylic acid (SA)-producing endophytic bacteria (EB)-44 and EB-47 isolates were pathogenic to N. benthamiana plants, the isolates were infiltrated into the leaves of N. benthamiana at a concentration of OD600 0.1
Summary
Endophytes comprise fungi or bacteria that colonize plant tissues without harming the host plant [1]. Bioactive compounds from endophytes, such as Bacillus, Pseudomonas, and Rhizobium, are known to promote host plant growth [2,3], whereas endophytic bacteria (EB) can confer resistance to pathogen-induced diseases in the host plant [4,5,6,7,8]. Bacterial species such as P. fluorescens (strain CHA0), P. aeruginosa (7NSK2), and Serrtia macrcescens (strain 90-166) produce salicylic acid (SA) and their colonization of host plants increases the endogenous SA levels, in addition to enhancing host defences [9,10,11]. To investigate the potential beneficial effects of SA-producing EB on host plants, we applied SA-producing EB to Nicotiana benthamiana and N. tabacum L. and evaluated resistance against wildfire disease, plant growth, and nicotine accumulation
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