. Cronartium comandrae in the Rocky Mountain States. Cronartium comandrae Rocky Mountains Region; Fungi Rocky Mountains Region. in plant communities near rust-infected lodgepole pine for long periods even though heavily infected by comandra rust almost every year. The combination of susceptible comandra shoots and general rainfall during the period aeciospores are being shed makes conditions suitable for primary infection, as the rust is usually common by mid-July on comandra near infected pine stands. The capability of aeciospores to germinate weU at prevailing cool temperatures also enhances
. Cronartium comandrae in the Rocky Mountain States. Cronartium comandrae Rocky Mountains Region; Fungi Rocky Mountains Region. in plant communities near rust-infected lodgepole pine for long periods even though heavily infected by comandra rust almost every year. The combination of susceptible comandra shoots and general rainfall during the period aeciospores are being shed makes conditions suitable for primary infection, as the rust is usually common by mid-July on comandra near infected pine stands. The capability of aeciospores to germinate weU at prevailing cool temperatures also enhances primary infection of comandra. By mid- July, aeciospores are reinforced by urediniospores as a source of inoculum. By this time, thundershowers generally prevail and spread becomes more hap- hazard. Because infection of comandra shoots takes only a short time, thundershowers usually result in some secondary spread. In most years infected comandra can commonly be found a few miles from infected pines, but in 1966, which was drier than normal in July and August, the rust in comandra was rare beyond a few hundred yards from infected pines. Apparently little secondary spread occurred in that year. Although telia are present from late July until hard frosts in autumn, basidiospores are cast only rarely. Not only were basidiospores rarely. JULY AUGUST Figure 21.~A successful suction trapping of basidiospores; and the corresponding weather data in Beaver Mountain plot 1966. trapped, but also visual observations indicated that basidiospore production had seldom occurred. Low temperatures prevent any appreciable cast at night during radiation dew periods even though relative humidity near comandra commonly reaches 100 per- cent for 4 to 6 hours. Moisture from thundershowers usually does not last long enough to initiate basidio- spore casting, but when it does, drying on succeeding sunny days greatly reduces chances of pine infection. By such action the potential of the inoculum may be
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