Effect of temperature, osmotic potential and pH on the growth of the turf pathogens Gaeumannomyces wongoonoo and Magnaporthe griffinii

Abstract

<p>The effects of temperature, osmotic potential and pH on the linear growth rates of two isolates of <i>Gaeumannomyces wongoonoo</i> and three isolates of <i>Magnaporthe griffinii</i> were studied. <i>G. wongoonoo</i> and <i>M. griffinii</i> grew maximally at 20-25°C and 25-30°C, respectively, which may explain their disease activity in the field from late spring to mid-autumn. The growth rate of <i>G. wongoonoo</i> was more than halved at about 15°C, and growth ceased at 10°C. Growth of <i>M. griffinii</i> was negligible at 15°C and ceased at 10°C. There was negligible growth of both fungi at 35°C. In response to osmotic potential, <i>G. wongoonoo</i> grew maximally at an osmotic potential of -0.12 MPa, while <i>M. griffinii</i> grew fastest at -1.0 to -2.0 MPa depending on the isolate. The growth rates of both fungi decreased linearly as the osmotic potential decreased, that of <i>G. wongoonoo</i> and one isolate of <i>M. griffinii</i> being minimal at -5.0 MPa, while the other two isolates of <i>M. griffinii</i> were capable of growth at -6.0 MPa, albeit very slowly. In response to pH, <i>G. wongoonoo</i> grew maximally at a pH 6.5-7.0, and the growth rate was halved at pH 5.0. In contrast, all three isolates of <i>M. griffinii</i> grew maximally at pH 5.0 and their growth rates were more than halved in the alkaline range (pH 7.0-8.0). These in vitro results provide a basis for more research into the activity of these fungal pathogens in field situations.</p>