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Techniques

Tan Spot of Winter Wheat: Procedures to Determine Host Response. P. J. Raymond, Former graduate student and research assistant, Department of Plant Pathology, Kansas State University, Manhattan 66506; W. W. Bockus(2), and B. L. Norman(3). (2)(3)Associate professor, and research assistant, respectively, Department of Plant Pathology, Kansas State University, Manhattan 66506. Phytopathology 75:686-690. Accepted for publication 15 January 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-686.

Techniques are described to quantify winter wheat cultivar reaction to tan spot under greenhouse and field conditions. A greenhouse seedling assay, which includes an improved technique for in vitro sporulation of Drechslera tritici-repentis, produced results which were highly correlated (r = 0.91) with those of field trials. The assay involves applying a conidial suspension (2 ? 10³/ml) to four-leaf seedlings in flats, exposing the inoculated plants to a 48 hr dew period in a mist chamber, and rating disease severity 7?10 days later. Preparation and use of inoculum for field experiments and a disease severity rating scale are described. When these techniques were employed under field conditions, a cultivar showing resistance in the greenhouse sustained 7.2% yield loss from tan spot compared to 27.7% for a cultivar identified as susceptible in the greenhouse. Under field conditions, ascospores were the only infecting propagules observed on leaves until 1 May when conidia were first detected and by 13 May only conidia were observed.