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Histology of Infection of Wheat by Tilletia indica, the Karnal Bunt Pathogen. Blair J. Goates, Agricultural Research Service, U.S. Department of Agriculture, Crops Research Laboratory, Utah State University, Logan 84322-6300, Present address: Agricultural Research Service, U.S. Department of Agriculture, Small Grains and Potato Germplasm Research, University of Idaho Research and Extension Center, P.O. Box AA, Aberdeen, Idaho 83210; Phytopathology 78:1434-1441. Accepted for publication 29 June 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/Phyto-78-1434.

Infection of wheat by Tilletia indica was investigated using scanning electron microscopy and light microscopy. Recently emerged spikes were inoculated by placing them beneath inverted petri dish cultures that were discharging secondary sporidia. Apparent hyphal anastomosis was observed rarely on the glume surface. Germ tubes arising from secondary sporidia penetrated through stomatal openings of the glume, lemma, and/or palea. Growth of germ tubes toward stomata was common. Approximately 90% of germ tubes that penetrated beyond the stomatal ledges did not pass between the guard cells and failed to enter the substomatal chamber. During the early stages of infection, intercellular hyphae were present among parenchyma and chlorenchyma cells in the distal to midportions but not basal portions of the glume, lemma, and palea and were absent from the ovary, subovarian tissue, rachilla, and rachis. Later, hyphae had grown intercellularly toward the floret base to the subovarian tissue and had entered the pericarp of the ovary through the funiculus. Hyphae were found in the rachis only during the later stages of infection. The epidermis of the ovary was not penetrated, even after prolonged contact with germinating secondary sporidia.