Neemazal, a product of neem (Azadirachta indica), induces resistance in pea (Pisum sativum) against Erysiphe pisi

The efficacy of neemazal, a natural product from neem (Azadirachta indica Juss.), against pea (Pisum sativum L.) powdery mildew (Erysiphe Pisi DC.) was studied in detached leaf and intact plant experiments. Neemazal significantly retarded several growth parameters of the pathogen, viz. multiple germ tube formation, numbers of germ tubes, branches and haustoria, and colony size on pea leaves. Neemazal induced hypersensitive reaction (HR), as evidenced by browning of host cells associated with appressoria. Furthermore, increase in protein concentration of intercellular fluids followed treatment with neemazal. Heat-shock of neemazal treated leaves reduced HR. Preinoculation treatment with neemazal was more effective in controlling disease development than post-inoculation application. The effect of the compound on the disease development was correlated with increased phenylalanine ammonia lyase (PAL) activity in pea leaves following treatment with neemazal. (C) 1997 Academic Press Limited.