TESTING VARIABILITY IN PATHOGENICITY OF PHYTOPHTHORA-CINNAMOMI

Forty eight isolates of Phytophthora cinnamomi from various host plant s in France (35 isolates) and in other countries were tested for patho genicity. Seedlings of chestnut, northern red oak, pine and eucalyptus were infected by soil contamination. Taproots, stems and bark strips of plants of chestnut and different oak species were inoculated with m ycelium agar disks. Results of the different experiments were in good agreement. All isolates appeared pathogenic to all the different test species but with variable levels of virulence. Isolates with consisten t low or high level of virulence, which could be used as standards in further studies, were identified. Interaction between P. cinnamomi iso lates and host plant species was significant in terms of lesion length s. These interactions could not be related to host from which P. cinna momi was isolated. Consistent with this, in Quercus rubra, the isolate -provenance interaction was not significant. This feature is encouragi ng for provenance screening for resistance to P. cinnamomi in this spe cies. The variation in virulence was not related to other isolate char acteristics (mating type, electrophoretic type, age).