Survival of Phytophthora lateralis in infected roots of Port Orford cedar

Short-term and long-term survival of Phytophthora lateralis in infected Port Orford cedar rootlets in soil was tested under a variety of conditions. Survival was measured by baiting infected rootlets with cedar foliage baits or by planting cedar seedlings into the infested soil. On the temperature gradient plate, recovery after 7 and 18 days at 10 degrees C was near 100%, but reisolation was sharply reduced from moist soil at 20 and 30 degrees C, and there was no recovery at 40 degrees C. In soil allowed to air-dry at the various temperatures, there was no recovery at 20 degrees C or above. Outdoors, the fungus survived at least 7 days in rootlets buried 10 cm deep in dry soil, and in rootlets on the soil surface, if shaded. There was no recovery from rootlets exposed to the sun. Temperatures did not exceed 25 degrees C in any treatment where the fungus was recovered. Long-term survival of P. lateralis in infected cedar roots was tested in litter bags buried in forest and cold frame conditions, and in intact root systems of cedar trees killed by I! lateralis. Direct isolation onto selective medium was attempted from forest trees killed at different times in the past. P. lateralis was not isolated from any tree dead for more than 2 years. The fungus was recovered by baiting from litter bags after 5 years but not after 6 years, and from root systems in buried pots through the 7 years of the test. Rate of recovery was sharply reduced in the last year in both cases.