Table 1 .-Influence of time on germination of aeciospores at cool, 

 moderate, and warm temperatures 



Germination Mean germ tube length 



Time Temperature (degrees C.) Temperature (degrees C.) 



(hours) ~8 18 28 8 18 28 



Percent Microns 



3 85 66 0.0 50 140 



6 78 66 0.0 126 278 



12 87 70 0.5 363 421 40 



24 94 72 1.0 451 495 95 



48 91 75 1.0 598 526 70 



Fresh urediniospores collected in July were 

 tested for their ability to germinate at various temper- 

 atures. Tests were run with spore samples from Cache 

 and Wasatch National Forests, and from greenhouse 

 plants that had been inoculated with Cache National 

 Forest spores. The techniques of collecting spores, 

 depositing them on test substrate, and analyzing 

 results were similar to those used in testing aecio- 

 spores. However, 2 percent water agar (about pH 6.7) 

 was used exclusively as the test substrate for uredinio- 

 spores. 



Germination of urediniospores was com- 

 monly by multiple germ tubes, one of which usually 

 became dominant (fig. 5), but single germ tubes were 

 frequent. Most viable urediniospores produced recog- 

 nizable germ tubes within the first 3 hours at favor- 

 able conditions, and germ tubes grew for more than 



Table 2.--Viability of aeciospores after exposure on coniandra shoots 



in a glasshouse 



Exposure time 

 (days) 



Germination^ 



Mean germ tube length^ 





Percent 



Microns 







34 



299 



5 



46 



300 



11 



20 



242 



21 



16 



209 



28 











^ Based on 200 spores. 



2 



Based on 10 germ tubes. 



became favorable for germination displayed no signs 

 of the rust. Comparison of measurements made with 

 thermocouples under similar conditions in Cache 

 National Forest suggests that leaf surfaces had com- 

 monly reached 25° to 35° C. at midday. This abiHty 

 of aeciospores to retain viability for even a few days 

 under severe summer field conditions certainly must 

 enhance spread of C. comandrae to comandra. 



UREDINIOSPORES 



Following infection, annual mycelium devel- 

 ops in leaves and stems of comandra. This soon gives 

 rise to uredinia, which rupture and expose hundreds 

 of yellowish elhpsoidal urediniospores. These spores 

 are disseminated by wind and function as secondary 

 inoculum for additional infection of comandra. This 

 spore stage can quickly intensify the rust in comandra 

 over distances of several miles. 



5 



