BASIDIOSPORES 



Basidiospores of rust fungi require a suitable 

 environment during dissemination to maintain via- 

 bility. Basidiospores of other conifer rusts have been 

 shown to be adversely influenced by high temper- 

 atures, low humidity, and sunlight (MacLachlan 

 1935, Hirt 1935, and Spaulding and Rathbun-Gravatt 

 1926). The influence of these factors was studied in 

 C. comandrae basidiospores. 



20 30 40 50 

 TIME IN HOURS 



Figure 10. -Germination of teliospores, based on 

 cumulative numbers of basidiospores 

 cast from telia in light and darkness. The 

 upper two graphs represent trials run in 

 the growth chamber. In the first, the 

 "light" group of telia was exposed con- 

 stantly at the 1,000-foot-candle level. In 

 the second, the "light" group was ex- 

 posed at regular intervals as shown. The 

 lowest graph represents the trial run in a 

 glasshouse, where the "Ught" group was 

 exposed to natural intervals of light and 

 darkness. Temperatures were held 

 constant in the growth chamber and 

 fluctuated somewhat in the glasshouse, 

 as shown by the dotted lines. 



Freshly formed basidiospores were collected 

 on glass slides and on 2 percent water agar. For col- 

 lection, glass and agar were exposed for 1 hour 

 beneath germinating teUa in moist chambers at 15° to 

 22° C. The basidiospores were immediately exposed 

 outdoors. During exposure, surface temperatures of 

 the glass and agar were measured with thermo- 

 couples. After exposure, the basidiospores were 

 incubated on 2 percent water agar at 18° C. for 24 

 hours. Viability was then measured by percent germi- 

 nation. 



Basidiospores were sensitive to exposure, but 

 survived sunlight well for at least 2 hours when kept 

 in contact with a moist substrate (table 7). Viability 

 dechned more quickly in basidiospores exposed 

 directly on glass, even when the slides were shaded by 

 lodgepole pine. 



The influence of relative humidity on reten- 

 tion of viability of basidiospores was studied. Basidio- 

 spores were obtained by exposing glass slides beneath 

 telia germinating at 18° C. in dark moist chambers. 

 After 1 hour of deposition, the slides were transferred 

 inside a mist chamber to dark chambers in which rela- 

 tive humidity was controlled by glycerol solutions as 

 described by Scharpf (1964). Following exposures of 

 2, 4, and 20 hours at controlled humidities, 

 basidiospores were transferred inside a mist chamber 

 to 2 percent water agar, and were incubated 24 hours 

 at 18° C. Spore viability was evaluated by percent 

 germination based on at least 200 spores. 



Relative humidity had a pronounced effect 

 on survival of basidiospores. Survival diminished with 

 increasing exposure time in less-than-saturated atmos- 

 phere (fig. 11) and decreased most rapidly at lower 

 humidities. It was only slightly better at 10° than at 

 20° C. Thus it would seem that only basidiospores 

 disseminated during damp weather would be viable. 



The influence of temperature on germi- 

 nation of freshly cast basidiospores was studied. 

 Spores were incubated in unlighted chambers in 

 which temperatures were controlled to an accuracy of 

 ±0.5° C. After incubation (24 hours except in time 

 tests), further germination was inhibited by appli- 

 cation of 1 percent chlorine. Percent germination, 

 based on at least 200 spores, and mean length of 20 

 germ tubes were then determined. 



The percentage of spores that germinated 

 increased for more than 24 hours at 8° and 28° C, 

 but reached its maximum in 6 hours at 18° C. (table 



10 



