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Growth of Haploid Tilletia Strains in Planta and Genetic Analysis of a Cross of Tilletia caries ? T. controversa. Frances Trail, Former graduate student, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902, Present address: Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY 14456; Dallice Mills, professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902. Phytopathology 80:367-370. Accepted for publication 2 November 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-367.

The growth of wild-type and genetically marked haploid strains of Tilletia caries and T. controversa was examined in susceptible and resistant wheat cultivars. Plants in the flag-leaf stage were inoculated by hypodermic injection of haploid strains of each fungus into the region of the developing head. Mutant and wild-type strains subsequently were recovered from wheat heads 3?6 wk after inoculation. Strains of compatible mating types of both fungi were crossed in planta and in wheat head organ culture, and the interspecific hybrid progeny were analyzed for segregation of mating type alleles and cycloheximide resistance. Drug resistance assorted independently of mating type among 101 F1 progeny, which is consistent with Mendelian assortment of unlinked genes. In the interspecific hybrid, the optimum temperature for teliospore germination was controlled by one or more dominant genes from the strain of T. controversa. The onset of germination was intermediate relative to T. caries and T. controversa and may be controlled by genes that are expressing incomplete dominance or that interact additively. These findings indicate that further genetic analyses will be very informative for ascertaining the genetic relatedness and species designation for these and other related bunt fungi.