Evaluation of Synergy between PGPR and Seaweed Extracts for growth promotion and Biocontrol of Rhizoctonia solani on soybean

Abstract

The necessity to increase crop yield is a constant pressure that farmers are faced with and chemical fertilizers and pesticides are the most effective method at this time. There are growing concerns towards the amount of synthetic chemicals applied to agricultural systems, especially regarding fertilizer runoff and unintended consequences of pesticides. Biostimulants are now experiencing an influx of research especially plant growth-promoting rhizobacteria (PGPR). PGPR have exhibited promising ability to promote plant growth via nutrient uptake, nutrient availability, and root growth stimulation via phytohormones. PGPR have also been reported as biocontrol microorganisms that secrete secondary metabolites and antibiotics to inhibit plant pathogen growth and colonization. Seaweed extracts are another category of biostimulants that are gaining traction as agricultural applications due to the newly developed extraction processes that help select for certain growth promotion and biocontrol traits. There are overlapping growth promotion and biocontrol mechanisms between these two biostimulants, which may offer an opportunity for synergy if applied together. The in vitro experiments demonstrated the ability of one seaweed extract formulation to act as a conducive environment for PGPR to grow. Through the in planta experiments we noticed a trend of biocontrol for Rhizoctonia solani across several treatments, but there were no significant differences. The growth promotion experiment showed significant growth differences compared to the control across several root growth parameters. The growth promotion assay revealed that the growth promotional effects of seaweed extracts are not dependent on the microorganisms, and instead most likely relies on the metabolites within the seaweed extracts.