The growth kinetics of the estuarine fungus Phytophthora polymorphica were examined in static liquid culture and on agar at four seawater salinities, 3, 15, 35 and 60 g sea salt l−1. In liquid culture accumulation of dry weight followed sigmoidal characteristics and an attempt was made to fit logistic equations to the growth curves. A highly significant fit of calculated curves was obtained for the measured growth data at 15, 35 and 60 g l−1, but not for 3 g l−1salinity. The maximum rate of dry weight production (0·37 mg h−1) and the highest specific growth rate (0·18 h−1) of mycelium were obtained at 15 g l−1salinity while both these growth parameters were significantly depressed at 3 g l−1(0·15 mg h−1; 0·11 h−1) and 60 g l−1salinity (0·16 mg h−1; 0·11 h−1). Possible reasons for this growth response are discussed. A calcium supplement was found to significantly reduce the growth inhibition caused by the lowest salinity treatment of 3 g sea salt l−1. Maximum radial growth rates occurred at 35 g l−1salinity (138 μm h−1) while radial growth rates were lowest at 3 and 15 g l−1salinity (42 and 63 μm h−1). P. polymorphica thus tolerates a wide range of sea-water salinities but biomass production and hyphal extension may be favoured by different salinity regimes. It is speculated that this may be an adaptation to the estuarine habitat of the fungus. © 1993, British Mycological Society. All rights reserved.
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