Ultrastructure of the host-pathogen interface of Peronospora viciae in cultivars of pea which show different susceptibilities

The ultrastructure of interactions of pea downy mildew ( Peronospora viciae ) on the leaves and petioles of two cultivars of pea, Superb and Maro, was examined. Tissue fixed at the time of sporulation (10 days after inoculation) revealed that many of the intercellular hyphae in Maro were showing evidence of partial or complete autolysis. The penetration matrices were enclosed in a thicker layer of callose-like material than in Superb, and many of the haustoria had collapsed, distorted profiles. Analysis of organelles lying close to the extra haustorial membrane revealed fewer associations with endoplasmic reticulum in Superb.