Structural resistance of cashew (Anacardium occidentale) against powdery mildew (Oidium anacardii)

Abstract

Studies were conducted in the laboratory at Wye College, University of London, to investigate some aspects of pre-infection structural resistance on cashew leaf and flower surfaces. Using the scanning, Transmission Electron Microscopes and the light microscope, cashew leaf surfaces were found to be covered by a layer of epicuticular wax, which  appeared to develop with age. Flower surfaces were found to be covered by hairs of varying shape and length which appeared to help trap tiny mildew spores. This appears to explain why flower organs are extremely susceptible to mildew infection. Using artificial inoculation, mildew infection was possible on young leaves, but infection did not occur on older leaves. Epicuticular wax layer observed on cashew leaf surface, as a pre-infection resistance factor, appeared to be responsible for inhibition of germination and development of O. anacardii on older leaves.

Keywords: structural resistance, cashew, Anacardium occidentale, powdery mildew, Oidium anacardii, Tanzania

Tanzania J. Agri. Sc.(1999) Vol.2 No.1, 115-125