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Cytology and Histology

Histopathology of Chrysanthemum Vascular Tissue Infected with Erwinia carotovora subsp. carotovora. Constance M. Smith, Graduate research assistant, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address of senior author: Biochemicals Department, E. I. du Pont de Nemours and Co., Wilmington, DE 19898; Robert S. Dickey, professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 71:148-151. Accepted for publication 25 July 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-148.

Chrysanthemum morifolium ‘White Marble’ plants were inoculated with Erwinia carotovora subsp. carotovora via the petiole of the first fully expanded leaf, whereas unrooted cuttings were inoculated via the petiole or at the base. All were placed under mist at 25 ± 5 C. Plants were also inoculated at the apex and grown in a greenhouse without mist at 23–30 C. Sections of vascular tissue of stems examined by light microscopy also were observed by scanning electron microscopy. Erwinia carotovora subsp. carotovora colonized but was restricted to, and caused limited or no degradation of, vascular tissue. Vascular infection did not lead to pith maceration although a host reaction of hypertrophic, hyperplastic parenchyma cells surrounding infected xylem was not evident. Individual bacteria were attached to vessel walls while masses of cells were present in some lumina. Unidentified material with a spongy appearance in scanning electron microscopy occurred within and between some infected vessels in the vicinity of pectic substances identified histochemically under light microscopy. The mechanism of tolerance of White Marble to E. carotovora subsp. carotovora is not clear. Whereas the hypertrophic, hyperplastic host response does not appear to be required in all cases, bacterial attachment to vessel walls and aggregation into masses surrounded by pectic material may be involved in confining the pathogen to vascular tissue.