VIEW ARTICLE

Aggregation of Host Cytoplasm and the Formation of Papillae and Haustoria in Powdery Mildew of Barley. William R. Bushnell, Research Plant Physiologist, Cereal Rust Laboratory, Agricultural Research Service, U.S. Department of Agriculture, University of Minnesota, St. Paul 55108; Susan E. Bergquist, Former Technician, Cereal Rust Laboratory, Agricultural Research Service, U.S. Department of Agriculture, University of Minnesota, St. Paul 55108. Phytopathology 65:310-318. Accepted for publication 2 October 1974. DOI: 10.1094/Phyto-65-310.

Living host cells in epidermal tissue partially isolated from barley coleoptiles were observed during penetration by Erysiphe graminis. The first visible response to the fungus was a well-defined aggregate of host cytoplasm which gathered beneath the appressorial tip of the fungus at 11.2 hours after inoculation. The aggregate contained rapidly-moving cytoplasmic organelles and persisted until 14.7 hours after inoculation. A papilla was produced at the center of many of the aggregates within 12.5-14.1 hours after inoculation. Haustoria were first seen 13.0 hours after inoculation, when aggregates were still present and when papillae were forming. Of a total of 251 appressoria from 10 host-parasite combinations, 94% produced cytoplasmic aggregates, 54% produced papillae, and 67% produced haustoria. Of the appressoria that failed to produce haustoria, 39-100% induced a papilla, depending on the host-parasite combination. Papillae and young haustoria were formed before the specific incompatibility conditioned by single genes in host and parasite was visibly expressed in three host-parasite combinations. The results suggest that the cytoplasmic aggregate has a role in the deposition of the papilla, and that the papilla is a significant component of generalized host resistance to powdery mildew fungi.