Secondary metabolites in black pepper (Piper nigrum) and their effect on the foot-rot pathogen Phytophthora capsici

Abstract

Most selection of black pepper are susceptible to the Phytophthora foot rot caused by Phytophthora capsici. Studies were undertaken to quantify the amount of secondary metabolites – piperine and oleoresins – in the vegetative plant parts of the susceptible selection KS27 tolerant selection P24 (both P.nigrum) and the resistant Piper species, P. colubrinum and to study if they had any effect on the vegetative growth of the pathogen in vitro. The P. nigrum selections KS27 and P24 especially the latter had higher concentrations of piperine in the roots than the leaves or stems. Synthetic piperine was found to inhibit the vegetative growth of P.capsici in vitro , at concentration of 0.4% and above. The oleoresin concentration was highest in the leaves, followed by the roots and least in the stem : the trend was the same in all three Piper plants with P. colubrinum recording the highest values. A significant inhibition in the growth of P.capsici was recorded when oleoresin from roots was incorporated in the media less so in that containing leaf oleoresin and an increase in growth in the presence of stem oleoresins. As the trend was the same in all three plants. No correlation could be drawn between inhibition of growth and susceptibility/tolerances resistance to P.capsici.