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The aerobiology of the aecial state of the commandra blister rust, Cronartium comandrae Peck, in Alberta. Powell , John Martin


Cronartium comandrae Peck is a heteroecious native rust which is damaging to several Pinus species in North America. It grows perennially in the living bark of hard pines producing pycniospores and aeciospores, and develops annually on species of Comandra and Geocaulon producing urediospores, teliospores and basidiospores. Studies were carried out to determine the effect of various meteorological and biological environmental factors on the aeciospore aerobiological phase of the rust. The main aspects considered included the factors affecting aeciospore production and release; and the factors affecting aeciospore transport, dispersion, deposition, germination and viability. Aeciospore production occurred from mid May to late August, with the peak period between late May and mid June. An average aecium produced spores for 35-50 days, and individual cankers produced spores for up to 95 days. Much variation occurred from year to year and between trees. Aecial production was interfered with by the activity of rodents, insects and other fungi on the canker and through resinosis, which probably accounted for a 50-55% reduction of the potential aeciospore production in any year. Fresh rodent damage was recorded on 40-52% of the cankers at about 20 locations in the years I966 to I968, insect damage on 39-46%, Tuberculina and Cladosporium infection on 17-33%, and resinosis on 67-71%. Rodent damage was mainly caused by squirrels. Some 64 micro-floral organisms were isolated from the cankers and spores. Tuberculina maxima was mainly responsible for killing the infected canker bark and greatly reduced the production of aeciospores. Penicillium spp. and an undescribed Cladosporium were also prominent on the cankers but played a lesser role in reducing production. One hundred and seventeen species of insects, mites and spiders were associated with the rust canker. Epuraea obliquus, an unidentified cecidomyiidae and Paracacoxenus guttatus were true mycetobionts. Various other species caused damage to the canker, including Dioryctria, Pissodes schwarzi and Cylindrocopturus deleoni. Daily aeciospore periodicity showed spores to be normally dispersed between 0800 and 1900 hours, with some evidence of a double peak between 1000 and 1600 hours, and little dispersal between 2000 and 0700 hours. Turbulent atmospheric conditions were associated with all peak aeciospore concentrations. Heavy rains initially increased spore concentrations, but no dispersal occurred during long humid cool periods. Spore deposition concentrations were very steep close to source, and showed a typical hollow curve deposition gradient. Spore concentrations from artificial release points were similarly reduced with distance from source, largely by diffusion. Aeciospores had an average velocity of 3.23 cm/sec in calm air. Rapid depletion of spore concentration occurred under the forest canopy, mainly by sedimentation, although aeciospores had good impaction efficiency. Aeciospores germinated on water agar over the temperature range 1-30°C, with optimum for germination and germ tube growth close to 15°C. Most aeciospores germinated within 4-5 hours, with a reduction in rate of germ tube elongation after 8 hours and little increase after 24 hours. Free water was necessary for germination; all spores swelled prior to germination. Aeciospores germinated equally well in the dark and light, and germinated over the pH range 4.5-8. Germination response on sugar media was better than on some other media, but addition of alternate host material to media did not improve germination. Daily aeciospore collections gave high germination percentages for 2-4 weeks, but much lower percentages during later sporulation period. Aeciospore germination was lower from exposed than protected aecia, and wet spores germinated poorly. Viability was reduced by contamination from associated fungi. Aeciospores lost viability very rapidly when exposed to temperatures above 25°C; temperatures close to 0°C were most favourable. High humidity affected viability, but ultra dry conditions were also adverse. Direct sunlight reduced viability rapidly. Generally, daily conditions favouring dispersal were least favourable for germination and viability retention.

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