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Cytology and Histology

Effect of the Systemic Fungicide 4-n-butyl-1,2,4-triazole on the Development of Puccinia recondita f. sp. tritici in Wheat. J. E. Watkins, Former Graduate Student, Plant Pathology, North Dakota State University, Fargo, ND 58102, (present address: Assistant Professor, Department of Plant Pathology, University of Nebraska, Lincoln, NB 68583); L. J. Littlefield(2), and G. D. Statler(3). (2)(3)Professor and Associate Professor, respectively, Plant Pathology, North Dakota State University, Fargo, ND 58102. Phytopathology 67:985-989. Accepted for publication 4 March 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-985.

The systemic fungicide 4-n-butyl-1,2,4-triazole (Indar; RH-124) applied as a seed treatment on wheat was taken up by the seeds and inhibited development of leaf rust caused by Puccinia recondita Rob. ex. Desm. f. sp. tritici Eriks. Treated seedlings of the near-isogenic wheat line Lr2 exhibited no macroscopic evidence of leaf rust 10 days after inoculation. Urediospore germination and subsequent stomatal penetration were not affected by the seed treatment. Plants from treated seed had fewer and shorter infection hyphae and fewer haustoria per infection site by 12 hr after inoculation than did the controls, but the differences were not significant until 36 hr after inoculation. The antifungal activity of Indar also was exhibited by swollen, distorted hyphae in leaves of treated plants. Beyond 36 hr, fungal development was almost completely inhibited. Indar appeared to restrict continued development of existing infection structures as well as the formation of new structures. The inhibitory effect of the test compound was not accompanied by necrosis in either the host or the pathogen, suggesting that the mechanism of this control differs from the hypersensitive form of rust resistance.