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Cytology and Histology

Histopathology of Syngonium podophyllum Artificially Inoculated with Xanthomonas campestris pv. syngonii. Cathy H. Zumoff, Research technician, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; Robert S. Dickey, Professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 77:1263-1268. Accepted for publication 20 March 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1263.

A histological study was made of Syngonium podophyllum ‘White Butterfly’ after inoculation with Xanthomonas campestris pv. syngonii to determine the development and effect of the pathogen in leaf, petiole, and stem tissues. The pathogen entered through the stomata of leaves sprayed with an aqueous suspension of the bacteria. The pathogen initially colonized substomatal and intercellular spaces of the spongy mesophyll and caused no apparent effects on surrounding cells even when initial water soaking was evident. As water soaking progressed, disruption of mesophyll cells occurred: Palisade and spongy parenchyma cells were surrounded by bacteria, followed by thinning and disruption of the cell walls. As the numbers of bacteria increased, they sometimes filled either large areas in the mesophyll or areas previously occupied by palisade cells. Bacteria did not occur in the vascular bundles of veins or rib veins. As inoculated leaves yellowed, dried, and shriveled, the tissues were compressed and became completely indistinguishable, and bacteria were not identifiable by light microscopy. X. c. pv. syngonii occasionally entered an uninjured petiole via stomata with subsequent development limited to substomatal and adjacent intercellular spaces. Petioles inoculated by needle-puncture with bacterial cells remained symptomless although the pathogen multiplied and eventually spread the length of the petiole and into the leaf but not the stem. The bacteria predominantly occurred in the intercellular and substomatal spaces at the periphery of the needle-punctured side; however, invasion and disruption of xylem tracheary elements occurred after needle inoculation. Evidence suggested that some of the damage to leaf and petiole tissues was mechanically produced by the bacterium. The pathogen was not isolated from or observed in stems of either leaf- or petiole-inoculated plants.