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Interaction of Wet Period and Temperature on Pyrenophora tritici-repentis Infection and Development in Wheats of Differing Resistance. R. M. Hosford, Jr., Professor, Department of Plant Pathology, North Dakota State University (NDSU) Fargo 58105; C. R. Larez(2), and J. J. Hammond(3). (2)Associate professor, Departamento de Agronomia, Universidad de Oriente, Jusepin-Monagas, Venezuela; (3)Professor, Department of Agronomy, NDSU. Phytopathology 77:1021-1027. Accepted for publication 30 December 1986. 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, 1987. DOI: 10.1094/Phyto-77-1021.

Increasing postinoculation wet period and/or temperature increased infection and disease development, but disease development in the resistant wheat was always less than in the susceptible. Infections (penetrations) were few, and lesions did not grow to visible size after 6 hr wetting at 10 C. Infections and visible lesions were few after 6 hr wetting at 20 and 30 C. Number and size of lesions increased and became abundant with lengthening wet period (12, 24, and 48 hr) at 10, 20, and 30 C. On tan spot resistant BH1146 and susceptible ND495 wheats in all wet periods and temperatures, conidia of Pyrenophora tritici-repentis produced similar numbers of germ tubes, appressoria, penetrations, and lesions. Germ tube growth and appressoria production increased with increasing wet period and temperature and stopped with termination of the wet period. As the wet period increased, papilla formation became twice as numerous in BH1146 as in ND495 but not enough to significantly affect the number of penetrations or lesions. Compared with ND495, resistance in BH1146 kept hyphal growth in the lesions, lesion growth, and growth in leaf area damage to approximately one-half and growth in lesion length to two thirds, with lengthening wet period and rising temperature. Resistance in BH1146 stopped lesion growth with rising temperature between 20 and 30 C. This resistance appeared to operate on a level smaller than organelle (molecular) in the leaf cells. Similar lesion spread beyond the mycelium in both wheats indicated a diffusible toxin from the mycelium that was not affected by lesion restricting resistance.

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