Foliar Application of Chlorella Supernatant Protects Turfgrass against Clarireedia jacksonii by Eliciting Induced Resistance and Modulating the Rhizosphere Microbiota

Large-scale culture of the microalga Chlorella produces valuable products. Cultivation also generates tons of supernatant waste that require detoxification and disposal. Recent research has focused on recycling waste supernatant as a plant protectant and biofertilizer, although, to date, most studies have considered its use as a biological control of pathogens infecting dicot plants. By contrast, the current study evaluated whether Chlorella supernatant could protect turfgrass (Agrostis stolonifera), a monocot plant widely used as a turfgrass, against dollar spot disease caused by the fungal pathogen Clarireedia jacksonii (formerly Sclerotinia homoeocarpa) under greenhouse and field conditions. Foliar application of supernatants from Chlorella sp. ABC001 and HS2 cultures reduced the incidence of dollar spot disease in turfgrass under both greenhouse and field conditions without directly inhibiting growth. The effects of supernatant application on the rhizosphere microbiome were investigated using 16S rRNA amplicon sequencing. Application of ABC001 and HS2 supernatants modulated the structure of the rhizosphere microbiome and enriched specific microbial taxa that improved turfgrass health in the presence of C. jacksonii. The application of waste Chlorella supernatant therefore offers an alternative method for protecting monocot plants against fungal pathogens, while also enhancing the composition of soil microbes in the rhizosphere.