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Physiology and Biochemistry

Translocation in Phloem Necrosis-Diseased American Elm Seedlings. E. J. Braun, Graduate research assistant, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Current address of senior author: Department of Botany and Plant Pathology, Iowa State University, Ames, IA 50011; W. A. Sinclair, professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 68:1733-1737. Accepted for publication 17 July 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1733.

Seedlings of Ulmus americana in their second season of growth were exposed to ¹⁴CO₂ and allowed to transport assimilated materials for periods of 4 to 24 hr. At the end of the transport period, samples consisting of the treated leaf, serial stem segments, and the root system were extracted in boiling 80% ethanol; extracts were analyzed for ¹⁴C. Healthy-appearing leaves on seedlings previously graft inoculated with the agent of phloem necrosis (PN) exported assimilate less rapidly than did leaves on healthy trees. Also, transport of ¹⁴C in stems of infected seedlings was impaired significantly prior to development of histopathologic symptoms in the secondary phloem. Translocation occurred, although slowly, in secondary phloem exhibiting histologic aberrations. These results indicate that callose deposition and sieve tube collapse, which are early symptoms of PN, are not solely responsible for the impairment of translocation in PN-diseased elms.