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Genetically Based Resistance of Eucalyptus marginata to Phytophthora cinnamomi. M. J. C. Stukely, Department of Conservation and Land Management, 50 Hayman Road, Como, Western Australia 6152; C. E. Crane, Department of Conservation and Land Management, 50 Hayman Road, Como, Western Australia 6152. Phytopathology 84:650-656. Accepted for publication 24 March 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-650.

Sixteen half-sib families of jarrah (Eucalyptus marginata) seedlings were screened for resistance to Phytophthora cinnamomi using soil inoculation and stem inoculation in pot experiments, and soil inoculation in a P. cinnamomi-infested field site. Low mortality following soil inoculation and short lesion lengths following stem inoculation were used as indicators of P. cinnamomi resistance. Resistance levels varied continuously across families from high to low values in all experiments, but family rankings were consistent among experiments. The narrow-sense heritability of the resistance character was high at both family (0.740.85) and individual-tree (0.43) levels. The resistance of jarrah to P. cinnamomi is under strong genetic control. Selection of lines with high levels of resistance is feasible, and such lines can be used in rehabilitation plantings of jarrah forest sites. Selection of resistant parent trees in the forest based on a single assessment of crown health met with little success. Seedlings of five healthy parent trees in diseased forest exhibited a wide range of resistance levels and were only marginally more resistant than seedlings of trees with symptoms of root rot. Stem-inoculation of jarrah seedlings at least 9 mo old is recommended as the standard screening test to be used in selecting families and individuals resistant to P. cinnamomi, based on lesion size.