Ultrastructure of the host–parasite interface in the fern rusts Milesia, Uredinopsis, and Hyalopsora (Pucciniastraceae, Uredinales)

Abstract

Species of the genera Milesia, Uredinopsis, and Hyalopsora possessed D-haustoria the necks of which were sheathed by an extension of the extrahaustorial matrix. Haustoria of the investigated species of Milesia and Uredinopsis were botryose with a haustorial body that formed wormlike protuberances. The Hyalopsora spp. were characterized by a vesicular haustorium. In the species of Milesia and associated Uredo spp. the haustorial neck was frequently differentiated into areas of variable electron density and structure; in Milesia blechni, Milesia miyabei, and Uredo RB 2537 a second neckband was formed in many haustoria. The penetration channels were usually characterized by short, perpendicularly oriented fibrillar elements that extended into the surrounding host cell wall. The haustoria of Uredinopsis filicina, Hyalopsora polypodii, and Hyalopsora aspidiotus were different from those of the investigated species of Milesia and Uredo. Their necks were accompanied by short extensions of the extrahaustorial matrix and the neck walls stained more or less homogeneously proximal to the neckband. Key words: Milesia, Uredinopsis, Hyalopsora, D-haustoria, ultrastructure, systematics.