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Challenge Appressoria of Erysiphe graminis Fail to Breach Preformed Papillae of a Compatible Barley Cultivar. James R. Aist, Associate professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; Hitoshi Kunoh(2), and Herbert W. Israel(3). (2)(3)Visiting associate professor, and senior research associate, respectively, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 69:1245-1250. Accepted for publication 16 May 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-1245.

To investigate the potential role of papillae in resisting fungal ingress, we tested the ability of Erysiphe graminis f. sp. hordei to form haustoria in host cells of a compatible barley cultivar at sites of preformed papillae. Oversize, preformed papillae were obtained by incubating inoculated coleoptiles on a Ca(H2PO4)2 solution from 924 hr after inoculation. These papillae had a heterogeneous ultrastructural appearance which differed substantially from that of normal papillae in barley coleoptiles. After the induction of preformed papillae, the fungus was removed from the epidermis, and a second (challenge) inoculum was applied. In two separate experiments, challenge appressoria located over papilla-free host wall areas had a normal percentage of haustoria, 72 or 52%; those over preformed papillae on the same two sets of coleoptiles had only 24 or 0%, respectively. The preformed papillae appeared to permit few or none of the appressoria located over them to form haustoria, depending on the experimental design. Appressoria located near, but not over, preformed papillae had an intermediate level of haustorium formation that may have been caused by substances diffusing from the papillae or by the papilla margins that were, presumably, too thin to be visualized by interference-contrast light microscopy. The results suggested that preformed papillae can prevent appressoria from producing haustoria in cells of a compatible host plant.

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