Effects of Water Stress on the Development of Cambial Lesions Caused by Cryphonectria cubensis on Eucalyptus grandis. W. J. Swart, Department of Plant Pathology, University of the Orange Free State, Bloemfontein 9300, South Africa. E. Conradie, M. J. Wingfield, and W. B. Venter. Department of Plant Pathology, Department of Microbiology and Biochemistry, and Department of Pasture Science, University of the Orange Free State, Bloemfontein 9300, South Africa. Plant Dis. 76:744-746. Accepted for publication 2 January 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0744.

The restriction of Cryphonectria cubensis to high-rainfall areas in South Africa has led to speculation regarding the influence of soil moisture on disease severity. A study was, therefore, conducted to determine whether a relationship exists between the development of Cryphonectria canker and water stress. Techniques involving axenic culture of the pathogen and artificial inoculation of 1-yr-old potted Eucalyptus grandis plants were employed. In culture, a significant negative correlation (r = 0.993; P < 0.01) was found between the growth of C. cubensis and osmotic stress induced by KCl. Pressure bomb assessment of the water potentials of inoculated plants indicated that drought-stressed plants (–2.5 MPa) developed smaller cambial lesions than nonstressed plants (–1.0 MPa). These results are in contrast with numerous reports on other canker pathogens in which drought stress is associated with increased growth of the pathogen.