Biocontrol of Rhizoctonia solani by water extracts from Chlorella sp. and Halopithys sp.

Water extracts from the green microalga Chlorella sp. and from the red macroalga Halopithys sp. were evaluated for their biostimulant effects and activity against the soil-borne pathogen Rhizoctonia solani on tomato. Extracts were applied on seed at 2.5, 5.0, 10.0 and 20.0 mg of dry biomass per mL of water. Both extracts increased seedling emergence by an average of 5.8%. Chlorella sp. extract increased seedling dry weight at all concentrations, particularly at 2.5 mg/mL (19.2%). Extract from Halopithys sp. increased dry weight only at 10.0 mg/mL (15.8%). Root rot disease caused by R. solani was reduced by Chlorella sp. extract at all concentrations, while the extract from Halopithys sp. reduced the disease at 10 mg/mL only. Both extracts did not reduce fungal colony growth; however, they caused abundant presence of hyphal cytoplasm coagulation.