Resistance of Micropropagated Eucalyptus marginata to Phytophthora cinnamomi. D. M. Cahill, School of Biological and Environmental Sciences, Murdoch University, Perth, Western Australia 6150. I. J. Bennett, and J. A. McComb. School of Biological and Environmental Sciences, Murdoch University, Perth, Western Australia 6150. Plant Dis. 76:630-632. Accepted for publication 24 January 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0630.

Eighty-eight percent of primary roots of a “resistant” micropropagated line of Eucalyptus marginata were able to restrict and confine colonization by Phytophthora cinnamomi. In contrast, no roots of susceptible seedling E. marginata restricted the pathogen. Lesions in roots of the field-resistant E. calophylla, the clonal line of E. marginata, and the unselected seedlings of E. marginata were 35 ± 11 mm, 51 ± 23 mm, and 125 ± 13 mm, respectively, 7 days after inoculation with P. cinnamomi. There was a highly significant (P < 0.01) difference between mean lesion length in roots of the clonal E. marginata and lesion length in roots of the unselected seedlings and a significant difference (P = 0.05) between clonal E. marginata and E. calophylla root lesion lengths. Screening seedling populations of E. marginata for resistance to P. cinnamomi followed by selection and micropropagation of “resistant” individuals may be a very useful strategy for developing resistance in an otherwise susceptible species.