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Histopathology and Ultrastructure of Vascular Responses in Peas Resistant or Susceptible to Fusarium oxysporum f. sp. pisi. B. J. Tessier, Department of Plant Sciences, University of Rhode Island, Kingston, RI 02881; W. C. Mueller, and A. T. Morgham. Department of Plant Sciences, University of Rhode Island, Kingston, RI 02881. Phytopathology 80:756-764. Accepted for publication 7 February 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-756.

A histopathological and ultrastructural examination of resistant and susceptible host-pathogen interactions was conducted in the garden pea cultivar Thomas Laxton following inoculation with race 1 and race 2 of Fusarium oxysporum f. sp. pisi. Responses were characterized and compared with healthy controls at 0.5, 1, 2, 3, 4, 6, 8, 10, and 12 days after inoculation. Vascular plugs, vessel coatings, callose deposits and phenolic compounds that accumulated as host responses were histochemically characterized. No qualitative differences were found to explain resistance or susceptibility. No anatomical or ultrastructural differences in response were observed between resistant or susceptible suscept-pathogen interactions up to 4 days after infection. After 4 days in susceptible interactions the pathogen grew laterally from initially infected vessels into adjacent vessels and parenchyma cells until the vascular bundle was completely colonized, while in resistant interactions the pathogen was confined to vessels initially infected. An increase in cytoplasmic activity of vascular parenchyma cells was detected in both resistant and susceptible interactions.