VIEW ARTICLE

Ecology and Epidemiology

Movement of Zoospores of Phytophthora cryptogea in Soils of Various Textures and Matric Potentials. J. M. Duniway, Department of Plant Pathology, University of California, Davis 95616; Phytopathology 66:877-882. Accepted for publication 29 January 1976. DOI: 10.1094/Phyto-66-877.

Active movement of Phytophthora cryptogea zoospores in soils was examined by placing susceptible safflower seedlings at various distances from a source of motile zoospores for 24 hours. The presence of P. cryptogea in seedlings was determined by symptom development and by isolation on a selective medium. Tension plates were used to control soil moisture at various matric potentials ( ψ _m). The bottom of soil samples 1.5-cm thick was the reference point for ψ _m values which are expressed in millibars (mb). Sporangia that formed in soil at ψ _m = –300 mb and were used to inoculate soils at higher ψ _m values only released zoospores at ψ _m ≥ –10 mb. When either sporangia or motile zoospores were used to inoculate soil, zoospores readily swam 25 to 35 mm in the surface water over flooded soils or through a coarse textured U.C.-type soil mix at ψ _m ≥ –1 mb. Active zoospore movement in the soil mix was reduced at ψ _m = –10 mb and was only detected over a distance of 5 mm at ψ _m = –50 mb. No detectable zoospore movement occurred at ψ _m ≤ –100 mb. Active zoospore movement in sieved and reconstituted silt loam and fine sandy loam soils was limited to a distance of 5 mm at ψ _m = –1 mb and was not detected at ψ _m = –10 mb. Zoospores moved a distance of 5 mm in a clay loam soil at ψ _m = –10 mb. Water flow down through 40 mm soil columns carried zoospores to depths of 8-12 mm in the loam soils and 40 mm in the coarse soil mix.