Studies of the infection of lupin leaves by Pleiochaeta setosa

Abstract

The penetration and establishment of Pleiochaeta setosa in lupin leaflets was studied with light microscope and scanning and transmission electron microscopes. Healthy lupin leaves were also studied at the ultrastructural level. Conidium germination, appressorium formation, and host penetration were found to take place non-synchronously, and the method of penetration of the pathogen through either the cuticle or stomata was determined by the method of inoculation. Disease symptoms were manifested 17 h after inoculation. The ultrastructure of stomatal penetration involved the formation of no specialized structures. Appressoria adhered to the host surface by means of adhesion blocks which penetrated the wax layer. Penetration through the cuticle was by a thin-walled infection peg that expanded below the cuticle to form a swollen infection hyphae from which hyphae ramified indiscriminately throughout the host. It is suggested that extracellular enzymes diffused in advance of the invading pathogen. The ultra-structure of the host reaction is described together with that of the invading fungus.