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Etiolated Apple Hypocotyls: a Useful Host Tissue in Apple Scab Research. R. L. Nicholson, Departments of Botany and Plant Pathology and Biochemistry, Purdue University, Lafayette, Indiana 47907; S. Van Scoyoc(2), E. B. Williams(3), and J. Kuc(4). (2)(3)(4)Departments of Botany and Plant Pathology and Biochemistry, Purdue University, Lafayette, Indiana 47907. Phytopathology 63:363-366. Accepted for publication 20 June 1972. DOI: 10.1094/Phyto-63-363.

A technique using etiolated apple hypocotyls was developed to observe developmental changes in the living apple-Venturia inaequalis interaction. These changes cannot be observed in living leaves because of tissue thickness and presence of pigments. Fungal growth and symptom expression of susceptible and hypersensitive interactions corresponded to those of green leaves. Microscopic symptoms in the hypersensitive interaction appeared as early as 30 hr before macroscopic symptoms. Cytoplasmic granulation and the accumulation of yellow-orange globules preceded extensive discoloration and death of host cells. As seedlings age, the extent of cell browning in the hypersensitive response is lessened and is often absent although stromatic growth of the fungus is inhibited. This suggests that inhibition of fungal growth cannot be completely accounted for by the oxidation of phenols.