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Cytology and Histology

Papilla Formation: Timing and Significance during Penetration of Barley Coleoptiles by Erysiphe graminis hordei. James R. Aist, Assistant Professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; Herbert W. Israel, Senior Research Associate, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 67:455-461. Accepted for publication 3 September 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-455.

Because Erysiphe graminis penetration pegs sometimes fail to penetrate host papillae, it has been suggested that the papillae can prevent haustoria from forming. We sought evidence for this suggestion by using interference contrast microscopy to monitor timing of papilla formation in relation to growth of E. graminis hordei penetration pegs into living barley (Hordeum vulgare) coleoptile cells. Papillae were formed at 85% of the 151 encounter sites studied. A substantial proportion (34%) of the papillae was formed long after pegs were initiated and was correlated with a high (84%) parasite penetration efficiency. Relatively few (12%) of the papillae were formed well in advance of pegs and these were correlated with a low (27%) penetration efficiency; this suggests that papilla formation is a disease-resistance mechanism. However, the papillae that formed before pegs did not delay development of the pegs or haustoria which subsequently formed. Furthermore, some penetration attempts failed even in the absence of papilla deposition, which suggests that other failures, associated with papillae, may also have occurred for reasons unrelated to papilla formation. Further experiments are required to show whether penetration failures are caused by papillae or by a deficiency in the potential of the fungus to complete penetration.