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Centrifugation Studies Help to Clarify the Role of Papilla Formation in Compatible Barley Powdery Mildew Interactions. Margaret A. Waterman, Graduate Research Assistant, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; James R. Aist(2), and Herbert W. Israel(3). (2)(3)Assistant Professor, and Senior Research Associate, respectively, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 68:797-802. Accepted for publication 24 October 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-797.

In compatible interactions between barley and Erysiphe graminis hordei, failures of fungal penetration are commonly associated with host papillae. To determine if papillae are responsible for these failures, and if enhanced papilla formation increases the percentage of failures, papilla deposition was experimentally altered in host cells. During attempted penetrations of coleoptile cells from fungal appressoria, the living coleoptiles were centrifuged sufficiently to produce two distinct zones [cytoplasm-rich (CR) and cytoplasm-poor (CP)] within individual host cells. Papilla deposition occurred at interaction sites in CR zones but not in CP zones. Using interference contrast microscopy, we observed the outcomes of penetration attempts from appressoria at pairs of interaction sites, one member of each pair located over each zone. Comparisons among the zones and noncentrifuged coleoptiles were made of two parameters: (i) the percentage of successful penetrations (penetration efficiency, PE); and (ii) the percentage of appressoria with pegs that failed to produce haustoria. In CP zones (where papillae did not occur) and noncentrifuged coleoptiles these parameters did not differ significantly. Therefore, we inferred that papillae do not cause the penetration failures that occur normally in this host-pathogen combination. Further data are needed to substantiate this inference. In CR zones, PE was only one third that in either the CP zones or in the noncentrifuged controls. Further, it appeared that in CR zones the only penetration attempts that were affected by the resistance response were by those appressoria that induced papillae. Thus, it appears that a centrifugally enhanced papilla (or some mechanism linked to papilla formation) has the potential to prevent fungal ingress.

Additional keywords: primary penetration, resistance, wall appositions, cytology, host-pathogen interactions.