VIEW ARTICLE

Limiting Influence of Low Water Potential on the Formation of Sporangia by Phytophthora drechsleri in Soil. J. M. Duniway, Department of Plant Pathology, University of California, Davis 95616; Phytopathology 65:1089-1093. Accepted for publication 26 April 1975. DOI: 10.1094/Phyto-65-1089.

The formation of sporangia by Phytophthora drechsleri was examined in soil at water potentials (ψ) between 0 and –150 bars. Soil and mycelial disks were air-dried separately to the desired ψ values and placed together in the chambers of thermocouple psychrometers. The psychrometers were subsequently used to measure and maintain ψ at nearly constant values. Crocks of soil equipped with thermocouple psychrometers were also dried to various ψ values before mycelia were buried in the soil. Sporangia were counted 4-12 days after mycelial disks were placed in soil. Large numbers of sporangia formed at ψ values between –0.3 and –4 bars, whereas few or no sporangia formed at ψ *0 or at ψ values lower than –4 bars. Variation in the period of time mycelial disks were in soil or the use of sterilized as opposed to unsterilized soil did not alter the influence of ψ on the formation of sporangia. Exposure of mycelial disks to ψ values less than –8 bars in soil inhibited subsequent formation of sporangia in water. P. drechsleri remained viable in soil at all ψ values down to –40 bars.