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Elongation of Secondary Hyphae and Transfer of ³⁵S from Barley to Erysiphe graminis f. sp. hordei during Primary Infection. Su- Chan Hsu, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823; Albert H. Ellingboe, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823. Phytopathology 62:876-882. Accepted for publication 14 February 1972. DOI: 10.1094/Phyto-62-876.

Over 70% of spores of Erysiphe graminis f. sp. hordei inoculated onto barley leaves develop secondary hyphae longer than 5 µ by 30 hr after inoculation with compatible parasite/host genotypes. The percentage is reduced with incompatible parasite/host genotypes, the actual percentage being dependent on the particular gene pair that specifies incompatibility. ³⁵S transfer from host to parasite also has been studied with compatible and incompatible parasite/host genotypes. The compatible parasite/host genotypes which had a high efficiency of infection also had high rates of ³⁵S transfer from host to parasite. The incompatible parasite/host genotypes which had low efficiencies of infection also had reduced rates of ³⁵S transfer from host to parasite. The three parasite/host genotypes in the quadratic check that specify compatibility by the criterion of final infection type show similar kinetics of ³⁵S transfer from host to parasite during primary infection.