Phytotoxic activity of Cercospora brachiata culture filtrate on seeds and aerial part of Amaranthus viridis

Slender amaranth (Amaranthus spp.) is considered a weedy species of difficult management and of great importance for agriculture. The objective of this work was to evaluate the phytotoxic activity of a extract filtrate produced by Cercospora brachiata, a foliar pathogen of A. viridis, on seed germination and development of slender amaranth, sorghum and cucumber plants. The fungus was cultivated in liquid culture media and the fungus extract obtained from the ethyl acetate extraction was concentrated and tested for phytotoxic activity on slender amaranth, sorghum and cucumber seeds and plants. For the seed test, 20 seeds of each species were transferred to Petri dishes containing germination paper soaked with 3 mL of each treatment: T1 (extract fungus + dimethylsulfoxide (CH₃) ₂SO), T2 (dimethylsulfoxide (CH₃) ₂SO) (white) and T3 (sterile water). For the plant experiment the same treatments described above were used, plus 0.05% Tween 80 (m v -1). Each plot contained one plant of each species per pot, five replicates and different phenological stages (2, 4 and 6 leaves). At each stage 3 applications of 3 mL planta-1 were made at 3 days intervals. The fungal extract of C. brachiata totally inhibited the germination of A. viridis seeds. Metabolites of C. brachiata show pronounced inhibitory activity on the growth of A. viridis plants and did not affect any physiological parameters for both cucumber and sorghum. Long chain acids and fatty acid esters were identified from the culture filtrate of C. brachiata.