Secretion in the Parasitic Phase of Rust Fungi

Rust fungi have a complex life cycle (see Littlefield 1981) and produce different spore forms. The basidiospores, aeciospores and uredospores develop highly specialized infection structures in order to penetrate into the leaf. The germ tune of the dikaryotic uredospore follows the array of wax crystals on the cuticle in a typical way and grows towards a stoma (Fig la). When the tip of the germ tube contacts the lip of the stomatal opening (see Hoch and Staples 1987) appressorium formation begins. From the lower surface of the appressorium, aninfection peg develops and penetrates into the substomatal cavity of the leaf where the substomatal vesicle with the infection hypha develops. After close contact with the parenchymatous host cells, a haustorial mother cell develops which, in turn, differentiates a haustorium in the host cell (Staples et al 1985). --