Fungicidal activity of pipernonaline, a piperidine alkaloid derived from long pepper, Piper longum L., against phytopathogenic fungi

Fungicidal activity of Piper longum L. fruit-derived materials toward six phytopathogenic fungi, Pyricularia oryzae, Rhizoctonia solani, Botrytis cineria, Phytophthora infestans, Puccinia recondita, and Erysiphe graminis, was tested using a whole Plant method in vivo. It was compared with synthetic fungicides (chlorothalonil, dichlofluanid and mancozeb) and four commercially available compounds (eugenol, piperine, piperlongumine, and piperettine) derived from P. longum. The response varied with the plant pathogen tested. At 1 mg ml^-1, the hexane extract of P. longum showed fungicidal activities against P. oryzae, B. cineria, P. infestans, and P. recondita with the control values of 33, 15, 40, and 100%, respectively. A piperidine alkaloid, pipernonaline, was isolated from the hexane fraction using chromatographical techniques and showed a potent fungicidal activity against P. recondita with 91 and 80% control values at the concentration of 0.5 and 0.25 mg ml^-1, respectively. Structural elucidation of pipernonaline was by means of MS, ¹H-NMR and ¹³C-NMR. In the test with commercially available components derived from P. longum, piperettine exhibited weak activity against E. graminis, but no activity was observed from treatments with eugenol, piperine, and piperlongumine. In comparison, potent fungicidal activity showed with chlorothalonil against P. infestans at 50 μg ml^-1, dichlofluanid against B. cinerea at 50 μg ml^-1 and mancozeb against P. recondite at 5 μg ml^-1. These results may be an indication of at least one of the fungicidal actions of pipernonaline derived from P. longum L. fruit.