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Cuticle Layer as a Determining Factor for the Formation of Mature Appressoria of Erysiphe graminis on Wheat and Barley. S. L. Yang, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823, Present address of senior author: Department of Physics, Mt. Sinai Hospital, New York 10029; A. H. Ellingboe, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823. Phytopathology 62:708-714. Accepted for publication 19 January 1972. DOI: 10.1094/Phyto-62-708.

Conidia of Erysiphe graminis produced high percentages of normal-appearing, mature appressoria on host leaves, the upper surface of epidermal strips, and on the upper surface of enzymatically isolated cuticles. Few normal-appearing, mature appressoria, or none, were formed when spores germinated on the lower surface of epidermal strips, on the lower surface of isolated cuticles, on reconstructed wax layers, or on a number of different artificial surfaces. Malformed appressoria were observed on plants that possessed eceriferum (cer) mutations which affect chemical components and the physical structure of wax layers. The Ml and Pm genes in barley and wheat, respectively, did not appear to interact with the corresponding P genes in the parasites to affect the morphological development of mature appressoria.