TEMPERATURE EFFECTS ON BASIDIOSPORE GERMINATION AND ON INFECTION OF SLASH PINE-SEEDLINGS BY CRONARTIUM-QUERCUUM F SP FUSIFORME

In vitro germination of basidiospores of 10 isolates of Cronartium que rcuum f. sp. fusiforme occurred within 24 h at temperatures of 8-32 C. At 32 C, only very short germ tubes developed. Germination was freque nt at temperatures of 12-28 C, and 90% of the maximum germination occu rred at 14.6-29.6 C. On the basis of second-degree polynomial regressi ons, the optimum temperatures during 24 h of moist incubation for the infection of pines were 17.7 and 19 C in two experiments. Moist incuba tion for 24 h at 11.6-23.4 C resulted in greater than or equal to 90% of the maximum infection rate for susceptible slash pine seedlings. Ba sidiospores were able to initiate infections over a broad temperature range of 8-28 C during a 24-h period of moist incubation. The shape an d height of curves for germination of each rust isolate or infection o f each pine family did not differ significantly, indicating neither fa ctor interacted with temperature.