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Inhibition of Tobacco Mosaic Virus by 8-azaguanine and 2-thiouracil in Diploid and Tetraploid Physalis floridana. D. E. Harder, Former Research Assistant, Department of Plant Pathology, Washington State University, Pullman 99163, Senior authorís current address: Department of Plant Science, University of Manitoba, Winnipeg 19, Canada; H. C. Kirkpatrick, Research Pathologist, Crops Research Branch, ARS, USDA, Tree Fruit Research Center, Washington Agricultural Experiment Station, Wenatchee, Washington 98801. Phytopathology 60:1255-1258. Accepted for publication 21 March 1970. DOI: 10.1094/Phyto-60-1255.

A tetraploid line of Physalis floridana was obtained by treating diploid P. floridana seed with colchicine. The 4N and 2N plants were used to test tobacco mosaic virus (TMV) multiplication and infectivity and the effectiveness of 8-azaguanine (8-AG) and 2-thiouracil (2-TU) as TMV inhibitors. Under greenhouse, laboratory, and growth chamber conditions, the 4N:2N TMV titer ratios were 2.05, 3.12, and 1.34, respectively. There was no difference in the specific infectivity of TMV from the 4N and 2N sources. Treatment with 8-AG and 2-TU inhibited TMV multiplication and reduced the specific infectivity of the recovered TMV in both 4N and 2N P. floridana. The inhibition of TMV multiplication by 8-AG ranged from 48 to 96% in 2N plants, and from 30 to 95% in 4N plants, depending on the method of application and concn of 8-AG. At 26 and 30 C, a single application of 8-AG stimulated TMV infectivity. At lower temp or with repeated applications, 8-AG reduced TMV infectivity. Under conditions providing a continuous supply of 8-AG to the infected leaves, specific infectivity was reduced 43.3% in 2N plants, and 48.6% in 4N plants.