INFECTION 



Comandra, jack pine, ponderosa pine, and 

 lodgepole pine have previously been infected with 

 comandra rust in experimental trials (Adams 1919, 

 Anderson 1960, Andrews et al. 1963, and Hedgcock 

 and Long 1915). However, virtually nothing is 

 reported about the processes of infection or the influ- 

 ence of moisture, temperature, or host phenology on 

 infection. Some information on these factors was 

 obtained in the following trials. 



COMANDRA 



of infection spots (evidenced by yellow color, swell- 

 ing, and uredinia) on test shoots were counted. 



Infection of comandra occurred over a wide 

 range of temperatures with both aeciospore and 

 urediniospore inoculum (table 9). Although infection 

 spots increased with longer mist periods, 12 to 24 

 hours was sufficient for abundant infection at mod- 

 erate temperatures. In foUowup trials, infection 

 occurred in as Uttle as 5 hours in a mist chamber at 

 about 20° C. 



Penetration of comandra was observed with 

 an incident light microscope and with a normal Ught 

 microscope when leaves were cleared by the 

 lactophenol-chloral hydrate technique (Riker and 

 Riker 1936) and stained with aniline blue. Both 

 aeciospores and urediniospores germinated well on 

 leaf surfaces. Appressoria formed when germ tubes 

 contacted stomates (fig. 13), and infection pegs could 

 be seen penetrating between the guard cells of 

 stomates. This was the only type of penetration seen 

 in comandra. 



The influence of temperature during inocu- 

 lation of comandra was studied under controlled con- 

 ditions. Comandra that had been growing in flats in 

 Logan for at least a year were used as test plants. At 

 the time of inoculation, shoots were about 2 months 

 old. Inoculum consisted of fresh aeciospores and 

 urediniospores originating in Cache National Forest. 

 Approximately equal numbers of spores were depos- 

 ited on test shoots by the settling tower method 

 described earher for aeciospore germination tests. The 

 flats were then placed in controlled temperature (±1° 

 C.) chambers in darkness. Distilled water was atom- 

 ized intermittently in the chambers and small water 

 droplets remained on leaves throughout the inocu- 

 lation. After specified times in the mist chambers, the 

 flats were moved to shaded portions of a well- 

 ventilated greenhouse until moisture on the shoots 

 dried (5 to 20 minutes). The flats were then placed 

 on greenhouse benches and shoots were examined 

 periodically for the presence of uredinia. A few days 

 after the emergence of the first uredinia, the numbers 



In other experimental inoculations, it was 

 easy to infect comandra shoots in a juvenile stage (1 

 week after emergence, when the purple shoots were 

 only a few centimeters tall), through maturity, and 

 until normal leaf abscission. Thus it appears that 

 comandra is highly susceptible at any stage of devel- 

 opment during the growing season. 



At greenhouse conditions of about 13° to 

 24° C, 10 to 15 days generally passed from the 



Figure 13.-Appressorium, at end of aeciospore 

 germ tube, attached to stomate of a 

 comandra leaf (X 850). 



13 



