Comparing Intraspecific Aggressiveness in Phytophthora cinnamomi Isolates

Phytophthora cinnamomi is a major plant destructive pathogen with a wide range of hosts and is considered one of the main causes of Quercus spp. decline in the Southwest of the Iberian Peninsula. This study compares two inoculation tests, using simple and fast methodologies, in order to select the most aggressive isolate to use in future Quercus suber inoculation experiments. To evaluate P. cinnamomi intraspecific variability, cork oak excised shoots were inoculated with five isolates, obtained from Q. suber, Quercus rotundifolia and Castanea sativa stands. These isolates were used for in vitro inoculation of a Trifolium subterraneum cultivar available in Portugal in order to assess its usefulness as a "model plant" in rapid screening tests. This study revealed intraspecific variability of P. cinnamomi isolates to cause lesions in Q. suber excised shoots and in the number of T. subterraneum developing lesions on stem and leaves. However, there was no correspondence between the aggressiveness of the isolates in subterranean clover and in the cork oak. Only one isolate showed consistency in aggressiveness regardless of the host species. In conclusion, T. subterraneum is not a good "model plant" for the evaluation of P. cinnamomi isolates aggressiveness.