VIEW ARTICLE

Inheritance of Tolerance to Carboxin and Benomyl in Ustilago hordei. Y. Ben- Yephet, Graduate Assistant, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel; Y. Henis(2) and A. Dinoor(3). (2)(3)Professor, and Associate Professor, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel. Phytopathology 65:563-567. Accepted for publication 10 December 1974. DOI: 10.1094/Phyto-65-563.

In Ustilago hordei, carboxin tolerance is controlled by polygenes, resulting in transgressive segregation for level of tolerance. Tolerance appeared to be monogenically or polygenically controlled, depending on the evaluation method: a single fungicide concentration revealed a 1:1 ratio, while a series of concentrations exposed transgressive segregation. Analysis of tolerance to benomyl was complicated by gamete inviability in crosses involving the benomyl-tolerant strain. On fungicide-free medium teliospores produced promycelia, but only 14% formed sporidia. The benomyl-tolerant strain had disturbances in meiosis with no effect on mitosis. Variation among offspring in their response to benomyl indicated polygenic control of benomyl tolerance. Teliospore germination in crosses involving carboxin-tolerant strains was normal, but on carboxin medium was lower than on complete media. Sporidia grew equally well on both media. In a mixed inoculation experiment, the benomyl-tolerant strain had a stronger sexual affinity for a compatible wild type than the carboxin-tolerant one. The benomyl-tolerant strain, competed successfully and eliminated the carboxin-tolerant strain, but was self-eliminating at teliospore germination. Biotype survival clearly depends on successful transmission through the sexual stage.