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Colonization of Wheat Seedlings by Cephalosporium gramineum in Relation to Symptom Development. M. V. Wiese, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823; Phytopathology 62:1013-1018. Accepted for publication 15 March 1972. DOI: 10.1094/Phyto-62-1013.

Wheat seedlings (Triticum aestivum L., ‘Genesee’) inoculated with a conidial suspension of Cephalosporium gramineum were systemically invaded by the fungus as early as 3 days after inoculation. The development of chlorotic leaf stripe symptoms followed fungal invasion of leaf blades and sheaths by 5 to 7 days. The fungus, predominantly in conidial form, invaded only the proto-and metaxylem vessels of occasional vascular bundles. In such vessels, conidial germination and blastogenous reproduction were common, and acropetal movement of the fungus occurred. Leaf striping was initiated around the fungus-containing xylem vessels, and laterally encompassed numerous layers of fungus-free cells including several adjacent uninfected vascular bundles. Prior to and in the early stages of leaf striping, the causal fungus was sparsely present in xylem vessels, and vascular occlusion was not apparent. During this time, healthy and diseased leaves showed equivalent capacities to conduct and accumulate dye solutions in their vascular bundles, but the lateral and intervenous transport of dye in diseased leaves was markedly impaired. The infected xylem vessels of prominently striped leaves frequently were occluded by conidial masses, and such leaves showed impaired conduction and accumulation of dye solutions. Thus, in Cephalosporium-infected wheat seedlings an initial interruption of lateral transport about infected vessels may contribute to leaf stripe formation. This dysfunction is distinct from the occlusion of the invaded xylem vessels which occurs later apparently as the result of fungus proliferation.