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Disease Control and Pest Management

Tolerance to Dodine in Venturia inaequalis . K. S. Yoder, Former Graduate Assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824, Present address of senior author: Biochemicals Department, E. I. duPont de Nemours and Company, Wilmington, Delaware 19898; E. J. Klos, Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 66:918-923. Accepted for publication 16 January 1976. DOI: 10.1094/Phyto-66-918.

Monoconidial isolates of Venturia inaequalis from Michigan were about half as tolerant to dodine as the least-sensitive New York isolate as determined by zone inhibition, germination in water solutions, and growth inhibition in broth. The most tolerant isolate crossed with normal isolates produced tetratype asci having four levels of tolerance suggesting additive action of at least two major independent genes for dodine tolerance. Testing of progeny from crosses of a green color mutant with isolates representing intermediate and high levels of tolerance indicated no close linkage between the genes for dodine tolerance and the green color gene of a known V. inaequalis linkage group. Inoculation experiments showed that isolate tolerance was a factor in scab control on trees treated with dodine at 4 µg/ml but not at 10 µg/ml. An ascospore abortion factor arising from the most tolerant isolates was not caused by the genes that conditioned higher levels of tolerance to dodine.