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Resistance

A Dominant Gene Conferring Disease Resistance to Tobacco Plants is Expressed in Tissue Cultures. J. P. Helgeson, Research Plant Physiologist, Agricultural Research Service, U.S. Department of Agriculture, Plant Disease Resistance Unit, Department of Plant Pathology, University of Wisconsin, Madison 53706; G. T. Haberlach(2), and C. D. Upper(3). (2)(3)Research Assistant Plant Physiologist and Research Chemist, respectively, Agricultural Research Service, U.S. Department of Agriculture, Plant Disease Resistance Unit, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 66:91-96. Accepted for publication 16 July 1975. DOI: 10.1094/Phyto-66-91.

Rooted cuttings and pith callus tissues from 185 tobacco plants were compared directly for their resistance to Phytophthora parasitica var. nicotianae, the causal agent of black shank of tobacco. Two plants, one homozygous resistant and the other homozygous susceptible, were used as parents. Plants tested were clonal cuttings from the resistant parent (resistant in 14 tests), clonal cuttings from the susceptible parent (susceptible in 14 tests), 13 progeny from the selfed susceptible parent (all susceptible), 19 progeny from the selfed resistant parent (all resistant), 42 F₁ progeny from a cross of the resistant and the susceptible parent (all resistant), 61 F₂ progeny from selfed F₁ individuals (45 resistant and 16 susceptible), 30 F₃ progeny from crosses of homozygous susceptible F₂ plants with heterozygous resistant F₂ plants (14 resistant and 16 susceptible), and 18 progeny from an outcross of an F₁ plant with susceptible Nicotiana tabacum ‘Wisconsin 38’ (11 resistant and 7 susceptible). In each case, plants that yielded resistant cuttings yielded only resistant callus, and plants that yielded susceptible cuttings yielded only susceptible callus. These results indicate that the single, dominant genetic factor which conferred disease resistance to intact tobacco plants was expressed in tobacco pith callus cultures. To our knowledge, our results constitute the first direct test of whether or not a gene for disease resistance in intact plants is also expressed in tissue cultures.