Pathogenicity of Pythium spiculum and P. sterilum on feeder roots of Quercus rotundifolia

摘要

Pathogenicity tests were conducted on 4-year-old Q. rotundifolia [Q. ilex] plants in Spain and Portugal inoculated with 9 isolates of Pythium spiculum, one isolate of Pythium sterilum, and one isolate of Phytophthora cinnamomi. One month after inoculation, the inoculated plants showed symptoms of root necrosis that resulted in foliar wilting followed occasionally by defoliation. Root damage severity exhibited significant differences relative to the control plants for all the isolates tested, with Phytophthora cinnamomi being the most pathogenic (average root necrosis value of 2.8). Isolates PE154, PA053, PA054, PA055, PE137, PE138 and PE144 of Pythium spiculum recorded root necrosis values (2.2) similar to isolate PE101 of Pythium sterilum (2.1), but significantly higher than isolates PE155 and PE156 of Pythium spiculum (1.6). This is thought to be the first report of Pythium spiculum causing root rot on Quercus in Spain and Portugal.