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Hexagonal Tubular Structures in Sieve Tubes of Apple Leaves. M. Weintraub, Research Station, Agriculture Canada, 6660 N.W. Marine Drive, Vancouver, British Columbia, V6T 1X2; R. Stace-Smith(2), and Bea Schroeder(3). (2)(3)Research Station, Agriculture Canada, 6660 N.W. Marine Drive, Vancouver, British Columbia, V6T 1X2. Phytopathology 65:660-663. DOI: 10.1094/Phyto-65-660.

Long, slightly curved tubular structures with a hexagonal cross-section and grouped into honeycomb arrangements were found in the sieve tubes of leaves from eight cultivars of apple trees. They were present in healthy control trees that had been indexed for, and found to be free from, known apple viruses, in trees infected with chlorotic leaf spot virus, and in trees that showed some witches’-broom symptoms of the foliage. The structures appear to be a normal component of apple leaf sieve tubes, and are not characteristic of apple trees suffering from proliferation disease.