Infiltration of Fungal and Bacterial Propagules into Soil

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Abstract
Phytophthora megasperma zoospores and cysts and Serratia marcescens cells were infiltered during the establishment of a gradient of matric potential in horizontally positioned columns of soil. Tensiometers placed in the soil columns were used to record matric potentials (in situ). In columns wetted a distance of 65 cm, zoospores moved 35 cm behind the wetting front in sand, 44 cm in sandy clay loam, 48 cm in loam, and failed to move in silt loam soil. In the sand, sandy clay loam, and loam soils, matric potentials of −14.5, −18.4, and −16.2 mbars, respectively, were calculated for soil at the boundary between infested and noninfested soils. Zoospore cysts moved one‐half the distance zoospores did in each soil, respectively. The matric potentials associated with their boundary were −13.2, −13.4, and −12.0 mbars. Serratia marcescens cells were recovered close behind the wetting front in the first three soils but 48 cm behind in the silt loam. The matric potential 48 cm behind the wetting front was −33.5 mbars. Attempts were made to develop a predictive model for infiltration of biological propagules based on propagule size and soil moisture characteristic curves. Results indicated that infiltration of propagules occurred after soil pores with radii considerably larger than a priori estimates of the limiting pore radii were filled with water.