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Effects of Wheat Genotype, Time After Inoculation, and Leaf Age on Conidia Production by Drechslera tritici-repentis. M. Riaz, Graduate student, Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506-5502, Present address: Agricultural Research Institute, Dera Ismail Khan NWFP, Pakistan; W. W. Bockus, and M. A. Davis. Professor, and research assistant, Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506-5502. Phytopathology 81:1298-1302. Accepted for publication 18 June 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-1298.

Regression analysis of the number of spores per leaf versus days after inoculation indicated a significantly higher slope (292.7) for a susceptible wheat cultivar (TAM 105) than for an intermediate cultivar (Triumph [93.5]) and two resistant cultivars (Karl [95.6] and Auburn [72.8]). When leaf age, expressed as position, was introduced as a variable, younger leaves produced spores less rapidly than older leaves for the resistant cultivar Auburn. Based on these results, cultivars that are resistant to Drechslera tritici-repentis will produce fewer conidia than susceptible cultivars, which should slow the secondary spread of the pathogen. Additionally, a procedure is described to quantify sporulation of D. tritici-repentis on wheat leaves. Leaves were harvested at various times after inoculation, placed on moist filter paper in petri dishes and exposed to alternating periods of 12 h light (35 ?mol m2 s1, 25 1 C) and 12 h dark (16 1 C) for 5 or 6 days. The number of spores produced per leaf then was determined.

Additional keywords: Pyrenophora tritici-repentis, yellow leaf spot.