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Effects of Wetting Period on Resistance to Leaf Spotting of Wheat, Barley, and Rye by Leptosphaeria herpotrichoides. R. M. Hosford, Jr., Professor, Department of Plant Pathology, North Dakota State University, Fargo, ND 58102; Phytopathology 68:591-594. Accepted for publication 19 September 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-591.

Leptosphaeria herpotrichoides was tested on plants of all of the following cultivars in all of the following sunlit wet periods. It caused no leaf spotting on any cultivar following postinoculation wet (mist) periods of 24 and 36 hr. Following wet periods of 48 hr it caused severe leaf spotting on Waldron, Red River 68, ND 495, and Marquis spring wheats and on Larker barley and Caribou rye. Chris spring wheat was less severely spotted and Leeds durum was slightly spotted. After 72-hr wet periods Chris and Leeds were severely spotted and Hercules durum was moderately spotted. Following 96-hr wet periods Hercules was still only moderately spotted. After 121-hr wet periods Hercules, Wells durum, and C306 spring wheat were severely spotted; Lodi oats was not spotted. This appears to be the first report of leaf spotting caused by L. herpotrichoides. The fungus requires a long postinoculation wet period to cause spotting. Expression of varietal resistance to leaf spotting was associated with the duration of the wet period. This phenomenon of varietal resistance, which is related to the duration of the postinoculation wet period, has now been detected with six leaf spotting fungal pathogens of wheat.

Additional keywords: synonyms: Phaeosphaeria herpotrichoides, (de Not.) L. Holm, Leptosphaeria culmifraga (Fries) Cesati & de Notaris.