The microbiome is an important determinant of plant health, growth and resistance to stress. Data for understanding and harnessing a species microbiome ecologically and agriculturally is needed. In addition, the application of cultured microbiomes to crop species has the potential for commercial product development to increase crop yields. This study was conducted to determine the effects of the phyllosphere-microbiome on managing Pseudomonas syringae pv. Glycinea (Psg), and the effects of the pathogen and microbiome on gas exchange and growth of soybeans (Glycine max L. Merrill).
A greenhouse study was conducted in the summer of 2019. Field isolated and cultured soybeans phyllosphere-microbiome was used to challenge soybeans in four independent treatment groups (control, microbiome only, microbiome and pathogen, pathogen only). Gas exchange, Psg density, chlorophyll concentrations, stable carbon and nitrogen isotopes and percent nitrogen in the leaves were measured in the V3-V6 stages of soybeans. Gas exchange was measured with the LI-6400xt Potable Photosynthesis System and CFUs were determined with the BioMate™ 3S Spectrophotometer. CHNS Elemental Analyzer was used to determine percent nitrogen and stable carbon and nitrogen isotopes while chlorophyll concentrations were determined using the MC-100 Chlorophyll meter.
Results/Conclusions
Data from fifty soybeans plants per treatment were collected for all variables and analyzed with the Minitab® 18 Software. There was a two-fold reduction in copies of Pseudomonas syringae pv. Glycinea per leaf disc in the microbiome-Psg treated group (P<0.005). The measured mean chlorophyll concentration doubled in the microbiome augmented treated group (P<0.0005). The microbiome had a significant positive effect on the dry shoot biomass (P<0.0005). Surprisingly, mean dry shoot biomass of the microbiome treated group was 5% higher than the control group P<0.05). The microbiome had a significant effect on the fresh weight of soybean nodules (P<0.0005) and the number of nodules (P<0.0005). Percent nitrogen per leaf disc was significantly higher in the microbiome treated plants (P<0.034). Furthermore, transpiration rate was significantly increased in the microbiome treated plants (P<0.0005). Interestingly, the water use efficiency of the microbiome treated plants was significantly reduced (P<0.013). Additionally, the mean ± SE Vcmax and Jmax of 113.44 ± 5.56 and 401.89 ± 35.42, respectively, of microbiome treated plants was 20% higher than pathogen treated plants.
The chlorophyll concentrations, dry shoot biomass, root nodules, transpiration, percent nitrogen and photosynthetic activity were significantly increased by the presence of the microbiome. Therefore, the phyllosphere-microbiome can be developed as plant probiotics against pathogens and for increasing crop yield.