Table 9.-Influence of temperature and time on infection of comandra in mist-chamber inoculation tests 



Inoculum and 

 time in mist 



chamber 



(hours) 



Mean number infections per leaf 



Temperature (degrees C.) 



13 



23 



28 



33 



Aeciospores: 















(Control)* 



























12 







5 



0,2 



6 



8 



Shoots died^ 



24 



0.1 



7 



7 



9 



8 





48 







8 



8 



26 



8 





/Z 



u 



o 



y 



Q 



y 



T ^ 



Zj 



Q 



o 





Urediniospores: 















(Control)* 



























12 



1 



4 



6 



9 



7 



Shoots died^ 



24 



2 



8 



7 



9 



10 





48 



3 



8 



11 



10 



10 





72 



5 



7 



11 



11 



10 





corresponding control group was set aside for each temperature series for each type of spore. 

 ^Apparently killed by environmental factors associated with the warm mist treatment and subsequent drying. 



beginning of an inoculation until uredinia emerged 

 through leaf surfaces, although the uredinia were 

 sometimes visible beneath the epidermis after only 6 

 or 7 days. Telia generally emerged 20 to 30 days after 

 inoculation, but in one instance they developed after 

 only 10 days had elapsed. Sometimes, especially late 

 in the growing season, the uredinial stage is bypassed 

 and only telia form. Artificial inoculations we made 

 in Cache National Forest in spring generally resulted 

 in uredinia in 2 to 3 weeks and teUa in 4 to 6 weeks. 



PINE 



All reported experimental infection of pines 

 has been with telial inoculum that had presumably 

 passed through the basidiospore stage before the 

 infection. Meinecke's (1929) attempts to inoculate 

 pines with aeciospores by his wounding and spore- 

 showering techniques, which were successful with 

 Peridermium harknessii, weie unsuccessful with C. 

 comandrae, as might have been anticipated with this 

 heteroecious rust fungus. 



The possibihty of mycelial transfer by 

 rodents and insects has also been investigated. More 

 than 1 00 attempts in the field to transfer the rust by 

 bark inserts and bark patch grafts (means used suc- 



cessfully by Hedgcock and Hunt 1920 and Patton 

 1962 with other conifer stem rusts) have failed for C. 

 comandrae. This might indicate that the odds are 

 against successful myceUal transfer by insects or 

 rodents, particularly under natural conditions that 

 would probably be harsher than those in the trials. 

 Therefore it seems reasonable that pine infection in 

 the field results only from infection by basidiospores. 



My attempts to detect penetration by means 

 of tissue clearing and incident-light microscopy have 

 failed, so the process of infection remains a mystery. 

 However, successful inoculations of seedlings give 

 clues to the influence of temperature and moisture on 

 infection and to the tissues that are susceptible. 



Method.-Lodgepole pines midway through 

 their third growing season were inoculated in a mist 

 chamber within a growth chamber. Temperatures 

 were controlled within the mist chamber ±1° C. and 

 the chamber was dark except in one experiment using 

 a programmed temperature cycle. ^ Inoculum from 

 Cache National Forest consisted of fresh comandra 

 shoots with viable telia, placed over the test pines. 



Seedlings were exposed to a cycle of 12 hours of 

 darkness at 5° C, followed by 12 hours of light (about 1,000 

 foot-candles) at 15° C. The test began with 3 hours of light. 



14 



