Control of potato late blight by exploiting the antimicrobial and biostimulant properties of exo-metabolites produced by Trametes versicolor

Potato late blight is a devastating disease affecting cultivated potato caused by the oomycete Phytophthora infestans. The use of biocontrol agents and plant resistance inducers are sustainable and alternative ways to fungicides to contrast the disease even at field level. In this study we tested the effect of the cultural filtrate (CF), derived from the growth in liquid culture of the basidiomycete Trametes versicolor, against potato late blight. The CF is rich of bioactive compounds with antimicrobial activities and capable to stimulate antioxidant system and promote plant defense. The CF can be used as crude culture filtrate (CCF), or by separating the components (i.e., polysaccharides, proteins, lipids). In vitro assays were developed to understand the effect of CCF and a protein fraction, precipitated with ammonium sulfate, on P. infestans. To investigate the antimicrobial capacity of CCF, 3-week-old plants were sprayed with CCF at different concentrations (0.25%-0.5%-1% w/v), detached leaves were infected with P. infestans, and the lesions were evaluated by trypan blue staining. To investigate the biostimulant capacity, CFF (0.25% w/v) was applied on potato plants by soil drench, and defense-hormones were evaluated by LC-MS/MS. CCF showed an antimicrobial capacity in vitro, by inhibiting sporangia germination and mycelium development, and the protein fraction seems to be the responsible for this activity. The same effect was noted in potato leaves sprayed with CCF, the treatment reduced the late blight severity about 40% respect to the control. For the biostimulant capacity, the plants irrigated with CCF showed an increase in the synthesis of the defense hormone (salicylic acid), suggesting the potential application to stimulate resistance towards P. infestans. In conclusion, the tests performed could be used to select the best strategy for applying CCF, or the single fractions, before attempting field trials.