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Deleterious Effects of Tobacco Smoke on Germination and Infectivity of Spores of Puccinia graminis tritici and on Germination of Spores of Puccinia striiformis, Pyricularia oryzae, and an Alternaria species. J. Stanley Melching, Research Plant Pathologist, Plant Disease Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Frederick, Maryland 21701; J. R. Stanton(2), and D. L. Koogle(3). (2)(3)Technical Assistant, and Technical Assistant, respectively, Plant Disease Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Frederick, Maryland 21701. Phytopathology 64:1143-1147. Accepted for publication 25 March 1974. DOI: 10.1094/Phyto-64-1143.

Uredospores of Puccinia graminis tritici and P. striiformis and conidia of Pyricularia oryzae and an Alternaria sp. were unable to germinate on 1.25% H₂O agar when 6,000 µliters of cigarette smoke/liter of air was in the incubation chamber. In control chambers without cigarette smoke the germination percentages for these organisms on agar plates ranged from 42 to 91. Decreased concns of smoke down to about 300 µliters inhibited germination; the magnitude of this effect varied with spore lot and with species. An additional incubation period in smoke-free air, following the smoke exposure, resulted in higher germination percentages if the original exposure to smoke was not greater than about 3,000 µliters. Exposure of agar to smoke before seeding with spores and incubation in a smoke-free atmosphere also inhibited or prevented germination, depending on the concn of smoke and the duration of exposure. Smoke from cigar and pipe tobacco had essentially the same effect as that described above. With P. graminis tritici, decreased germination at inhibitory smoke concns was because the rates of germ tube emergence and elongation during the first 2 h of incubation were greatly reduced. When the incubation period was increased from 2 h (the time usually sufficient for uninhibited spores to achieve maximum germination) to 6 h, mildly inhibited spores caught up with the no-smoke control spores in percentage germination values, but the average length of their germ tubes was one-half that of the control spores. Exposure of dry uredospores to 6,000 µliters of cigarette smoke/liter of air did not affect their subsequent germination on agar or their ability to infect wheat seedlings when used as inoculum. However, when agar plates were seeded and wheat was inoculated with spores of proven infectivity and incubated in dew chambers in 3,000 µliters of smoke/liter of air, germination was decreased and essentially no infection occurred.