Comparative ultrastructure of the haustoria in uredial and pycnial infections of Puccinia coronata avenae

Abstract

The haustorial apparatus in uredial infections of P. coronata in Avena sativa was essentially similar to that reported elsewhere for the cereal rusts. Further evidence was obtained that membranes of some host cytoplasmic vesicles were continuous with the invaginated host plasmalemma. The intracellular structure in pycnial infections of P. coronata in Rhamnus cathartica remained confined to and established a long-term relationship with the host cell, thus qualifying it as a haustorium (designated P haustorium). The P haustoria were less specialized than uredial haustoria and differed from them in the following ways: the P haustorium mother cell did not appear to be attached to the host cell, and there was no localized thickening of the fungal wall at the penetration site; there was no specialized penetration peg; an ingrowth of host wall-like material formed in advance of the penetrating fungus and the remnants of the ingrowth later formed a collar around a necklike portion of the P haustorium; there was no well differentiated neck and no neck ring; the P haustoria were very irregular in shape with sharply contoured outlines and were occasionally septate; the P haustorial protoplasts were more densely staining and contained large amounts of lipid and glycogen storage material; there was an irregularly occurring sheath around the P haustoria; and the host vascular tissue was invaded by intercellular and intracellular growth in pycnial infections.