The aggressive and non-aggressive strains of Ceratocystis ulmi have different temperature optima for growth

Abstract

The aggressive and non-aggressive strains of Ceratocystis ulmi exhibit markedly different temperature-growth responses in vitro . The optimum temperature of the aggressive strain (both EAN and NAN races) was 20–22°C and that of the non-aggressive strain was c. 30°. The upper limit for growth of the EAN aggressive was c. 32% of the NAN aggressive c. 33°, and of the non-aggressive strain c. 35° Two temperatures, 20 and 33°, are now recommended for separating the strains on the basis of growth-rate. The ranking order of the strains at 20° is the reverse of that at 33° and this provides a qualitative method for routine strain identification. The significance of the different temperature-growth responses of the two strains is discussed.