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Cytology and Histology

Contact with Membrane Grooves Induces Wheat Stem Rust Uredospore Germlings to Differentiate Appressoria But Not Vesicles. Richard C. Staples, Boyce Thompson Institute for Plant Research, Ithaca, NY 14853, USA; Hans-J. Grambow(2), Harvey C. Hoch(3), and Willard K. Wynn(4). (2)Institut für Biologie III, RWTH Aachen, D-5100 Aachen, B.R.D.; (3)New York State Agricultural Experiment Station, Cornell University, Geneva 14456, USA; (4)Department of Plant Pathology, University of Georgia, Athens 30602, USA. Phytopathology 73:1436-1439. Accepted for publication 11 April 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1436.

The capacity of uredospores of the wheat stem rust fungus, Puccinia graminis f. sp. tritici (races 32 and 56), to develop infection structures in response to contact stimuli was reexamined. Uredospores were germinated on a variety of membranes that were scratched by rubbing them with steel wool or carborundum, and examined for nuclear division and differentiation. These responses were compared with those obtained on the membranes after a heat shock or stimulation with acrolein. The results showed that germlings underwent one round of nuclear division (four nuclei) and formed appressoria abundantly in the grooves on scratched sheets of polystyrene, polyethylene, or aluminum foil. The infection structures did not develop further. Differentiation of appressoria also occurred on scratched glass and cellulose, but the frequency of response was low. Complete infection structures (appressorium, peg, vesicle, and infection hypha) developed when the germlings were stimulated by heat shock or by acrolein (1.5 x 10^-9 M), but the appressoria were located randomly on the surfaces. These structures had at least eight nuclei. We concluded that contact stimuli serve to position appressoria over stomata, but development of the vesicle may require other factors, apparently from the host.