Use of extracts from Prosopis nigra in the control of Cercospora kikuchii and Septoria glycines

Abstract

The antifungal activity of organic extracts from leaves, bark and hearthwood of the timber tree Prosopis nigra was investigated against fungi responsible for soybean late season diseases. Nine extracts were assayed by the disc diffusion test toward Septoria glycines and Cercospora kikuchii. The methanol extract of leaves was the most active with the lowest inhibitory dose of 200 μg disc−1 on both fungi and diameters of growth inhibition zones of 18.5 mm (C. kikuchii) and 20.5 mm (S. glycines). Tryptamine was the main antifungal constituent of the extract. The methanol extract and tryptamine synergized the effect of difenoconazole. Tryptamine also inhibited cercosporin produced by C. kikuchii in 36–96 % when applied at 25−100 μg and 70 % when provided in mixture with the fungicide. Preventive applications of the extract and the mixture on soybean plants strongly reduced disease severity produced by both fungal pathogens. Our results indicate that the leaf methanol extract of P. nigra deserves further research as an additive of azole fungicides applied for the control of C. kikuchii and S. glycines.