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Ecology and Epidemiology

Use of Fluorescent Antibodies to Study the Survival of Phytophthora megasperma and P. cinnamomi Zoospores in Soil. J. D. MacDonald, Assistant, Department of Plant Pathology, University of California, Davis, 95616; J. M. Duniway, associate professor, Department of Plant Pathology, University of California, Davis, 95616. Phytopathology 69:436-441. Accepted for publication 17 October, 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-436.

Zoospore cysts of Phytophthora megasperma and P. cinnamomi were added to nonsterile soil and its matric potential was adjusted to predetermined values. The infested soils were held under laboratory and field conditions and periodically sampled to determine cyst viability and soil water potential. During sampling, soil containing cysts was suspended in water and aliquots were placed on a selective agar medium to allow germination of viable cysts. After germination, the cysts were stained by an immunofluorescence detection technique and counted. Under laboratory conditions, zoospore cysts of P. megasperma survived no longer than 3 wk at water potentials ranging from 0 to 15 bars, and under field conditions they survived no longer than 2 wk. Zoospore cysts of P. cinnamomi survived no more than 3 wk in soil at water potentials of 0 to 1 bar under either field or laboratory conditions. However, at water potentials of 5 or 15 bars, zoospore cysts of P. cinnamomi survived up to 6 wk in the laboratory. In a nonirrigated field plot, in which soil water potentials ranged from 7 to less than 100 bars, cysts of P. cinnamomi survived for 810 wk. Under more controlled humidity conditions, zoospore cysts of P. cinnamomi proved relatively tolerant of desiccation; many survived for 1 wk in soils that dried to water potentials as low as 75 bars. Compared to P. cinnamomi, zoospore cysts of P. megasperma were much more sensitive to desiccation; most were killed within 1 wk in soil dried to water potentials of 20 bars or less.