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Interaction of the asc Locus in F8 Paired Lines of Tomato with Alternaria alternata f. sp. lycopersici and AAL-Toxin. S. D. Clouse, Department of Plant Pathology, University of California, Davis 95616, Present address: Plant Biology Laboratory, Salk Institute, P.O. Box 85800, San Diego, CA 92138; D. G. Gilchrist, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 77:80-82. Accepted for publication 25 April 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-80.

Purified AAL-toxin and single conidial isolates of Alternaria alternata f. sp. lycopersici were used to analyze F8 paired lines of tomato for their respective interaction with the asc locus. Reaction to the pathogen was inherited as a single locus dominant for resistance in a segregating F9 population of 2,064 plants derived by selfing progeny tested F8 asc+/asc plants obtained by intercrossing F7 asc+ / asc+ and asc / asc full-sibs. Reaction to the AAL-toxin and the pathogen, assessed simultaneously on 390 F9 progeny from a single F8 asc+ / asc plant, showed no independent assortment for the two reactions. The parental (asc+ and asc), F1 (asc+ / asc). F9 (asc+ and asc), and F8 (asc+ / asc) plants revealed three significantly different levels of toxin sensitivity, which were inherited as an incomplete dominant and corresponded to the genotype at the asc locus.