The Effect of Temperature on the Growth of the Fireblight Pathogen, Erwinia amylovora

S ummary . Growth rates of Erwinia amylovora in yeast extract–peptone broth were assessed, by colony counts and turbidity measurements, at c. 3° intervals over the range 6.5–36.0°. An Arrhenius plot showed a linear relationship between doubling rate and temperatures between 9 and 18°. The slope of this line was comparable to that obtained for Escherichia coli by Ingraham (1958) between c. 12 and 30°. At 18° there was a sharp change in growth rate; between 18 and 28° the doubling time decreased only from 2.1 to 1.3 h (Q 10 = 1.8) but between 8 and 18° it increased from 2.1 to 14.0 h (Q 10 = 6.7). This apparently critical temperature is of special interest because maximum air temperatures > 18° appear necessary for epidemic blossom blight in North America.