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Factors Limiting the Transmission of a Xylem-Inhabiting Bacterium Clavibacter xyli subsp. cynodontis to Grasses by Insects. Raymond V. Barbehenn, Department of Entomological Sciences, University of California, Berkeley 94720, Current address: Department of Biology, University of Michigan, Ann Arbor 48109-1048; Alexander H. Purcell, Department of Entomological Sciences, University of California, Berkeley 94720. Phytopathology 83:859-863. Accepted for publication 21 April 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-859.

We investigated the potential of phytophagous insects to transmit Clavibacter xyli subsp. cynodontis to bermudagrass and maize. Neither leaf-chewing nor xylem-sucking insects transmitted the bacterium after feeding on colonized plants. C. x. cynodontis was readily transmitted to bermudagrass and maize by mechanical inoculation of their stems, and Schistocerca nitens (Orthoptera: Acrididae) transmitted the bacterium to bermudagrass when concentrated cell suspensions were applied to their mouthparts and feeding was restricted to stems. The factors limiting the transmission of C. x. cynodontis by chewing insects under natural feeding conditions include the low susceptibility of leaves (vis--vis stems) to C. x. cynodontis colonization, the small numbers of the bacterium acquired by insects fed colonized foliage, and the retention of relatively few viable bacteria on the mandibles of insects.

Additional keywords: Cynodon dactylon, Homoptera, Lepidoptera, Zea mays.