VIEW ARTICLE

Physiology and Biochemistry

Cell Death and Membrane Leakage Not Associated with the Induction of Disease Resistance in Peas by Chitosan or Fusarium solani f. sp. phaseoli. David F. Kendra, Graduate student, Department of Plant Pathology, Washington State University, Pullman 99164-6430; Lee A. Hadwiger, Professor, Department of Plant Pathology, Washington State University, Pullman 99164-6430. Phytopathology 77:100-106. Accepted for publication 24 June 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-100.

No correlation was found between disease resistance and host cell death and membrane leakage in the interactions between pea endocarp tissue and Fusarium solani f. sp. pisi (compatible) or F. s. f. sp. phaseoli (incompatible). Initially, the pea endocarp tissue responds to both the compatible and incompatible pathogens. After inoculation, both fungi germinated, but their growth was suppressed within 5 hr. However, within 24 hr, the compatible, but not the incompatible, pathogen resumed active growth. Host cell viability as measured by the vital stains, fluorescein diacetate (FDA) and phenosafranin, was still apparent in the incompatible interaction beyond 17 hr postinoculation. At this time, some host cells were also beginning to develop into a hypersensitive response, and cell viability was absent in cells near multiple conidial attachment sites. Viability was reduced more rapidly in the compatible interaction. Fungal cell viability in the presence of chitosan was related to both the chitosan concentration and the length of the exposure. The initial growth inhibitory effect of chitosan is probably not due to a reduction in fungal cell viability since the fungal tissue retained the ability for regrowth and remained FDA fluorescent following exposure to growth suppressing levels of chitosan. Changes in conductivity due to release of electrolytes from damaged plant tissue after fungal inoculation or chitosan treatment did not correlate with disease resistance. However, a sharp increase in electrolyte leakage was observed after 48 hr in the compatible interaction. Chitosan also failed to enhance the release of electrolytes from formae speciales of F. solani at concentrations which suppress their germination and growth.