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Cytology and Histology

Invasion of Phloem and Xylem of Woody Stems and Roots of Eucalyptus marginata and Pinus radiata by Phytophthora cinnamomi. E. M. Davison, Department of Conservation and Land Management, Como, Western Australia 6152; M. J. C. Stukely, C. E. Crane, and F. C. S. Tay. Department of Conservation and Land Management, Como, Western Australia 6152. Phytopathology 84:335-340. Accepted for publication 7 December 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-335.

Woody stems and roots of field-grown Pinus radiata (pine) and Eucalyptus marginata (jarrah) were inoculated with Phytophthora cinnamomi, and the progress of invasion was investigated by sampling wood and bark 1, 3, 6, and, in some cases, 12 wk after inoculation. P. cinnamomi rapidly invaded phloem and xylem of both species, and a hemibiotrophic infection developed in the phloem. In jarrah and in some pine stem and root samples, an inapparent infection was established in the xylem, but in other pine samples, invaded wood became dry and/or resin soaked. This fungus persisted longer in and was more frequently isolated from wood than from bark. In jarrah, xylem invasion was confined to a narrow band adjacent to the cambium, whereas in pine wood radial invasion was more extensive. In some pine stems, a segment of nonconducting wood formed adjacent to the inoculation point; this did not occur in jarrah. Tissue invasion in both species was less extensive after inoculation during autumn than during spring. In all experiments, invasion was restricted by host responses to infection.