Roles of Matric and Osmotic Components of Water Potential and Their Interaction with Temperature in the Growth ofFusarium oxysporumin Synthetic Media and Soil

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Abstract
Interactions of water potential, both matric and osmotic, and temperature as they affect radial growth of F. oxysporum were studied. Water potential (.phi.) was adjusted osmotically with KCl and MgCl2 and matrically in sterile and nonsterile field soil and with polyethylene glycol (PGE) 6000, a suspended matricum. High temperatures were more inhibitory to growth in matrically adjusted than in osmotically adjusted media. Growth decreased steadily with decreases in soil matric .phi.; however, growth in osmotica was stimulated as .phi., declined from -8 to -15 bars. At osmotic potentials < -20 bars, MgCl2 as a solute was more inhibitory than KCl. PGE, for which a method of radial growth determinations is described, affected growth < -10 bars similarly to the osmotica. The effects of temperature and .phi. on growth in sterile and nonsterile soil were similar. Growth responses obtained on any of the synthetic media tested, adjusted either osmotically or matrically, did not adequately represent those obtained in soil. Inferences concerning the role of soil .phi. in fungal ecology cannot be drawn from studies in which .phi. is adjusted osmotically or by the use of a suspended radial growth as a function of matric .phi. in sterile and nonsterile soil.

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