The scenario suggested here may explain the pattern of teliospore production obtained by 

 Clinton and McCormick (1924). They made several hundred aeciospore and urediospore inoculations 

 over 3 years on detached leaves of many different ribes species. Their cultures were grown in 

 a greenhouse, so they were not able to exercise much control over temperature. Over years 

 they attempted 131 inoculations v\fith aeciospores (not single spores) during April, May, and 

 June and obtained 83 infections (63 percent success). Of the 83 infections, 2 (2 percent) 

 produced teliospores within 3 weeks (their cultures apparently did not live much beyond 3 

 weeks although they did not explicitly state any average age). In addition, they obtained 

 about 47 infections from urediospores . Of these, 34 were inoculated between September 13 and 

 17, 1918, of which 22 (65 percent) produced teliospores. Of 49 infections obtained from 

 urediospore inoculation during April, May, June, July, and August, only 14 percent produced 

 teliospores. If we assume that their cultures lasted an average of 21 days and that only the 

 September 13 to 17, 1918 period was cool enough, our results could be interpreted as being in 

 total agreement with theirs. 



New attempts at isolation of single aeciospores should be conducted at a cool temperature, 

 55 F (13 C) . Time required to complete the life cycle in isolation can be reduced by reinocu- 

 lating with urediospores as soon as they are produced. Also, early teliospore production by 

 certain single aeciospore-derived infections may indicate the existence of yet another 

 C. ribicola marker gene as well as having possible important significance to the epidemiolo- 

 gical relationships of C. ribicola. Other rust species may have responded in a like manner 

 (Savile 1953) in their adaptation to short seasons. Genetic control of a trait such as 

 teliospore production by infections arising from different spore stages as well as variation 

 among individual spores could indicate the operation of a fundamental adaptive device that 

 might have its ultimate expression in the formation of microcyclic races. 



PUBLICATIONS CITED 



Clinton, G. P., and F. A. McCormick. 



1924. Rust infection of leaves in Petri dishes. Conn. Agr. Exp. Sta. Bull. 260, p. 475- 

 501. New Haven, Conn. 

 McDonald, G. I. 



1978. Segregation of "red" and "yellow" needle lesion types among monoaeciospore lines of 

 Cronartium ribicola. Can. J. Genet. Cytol . 20:313-324. 

 McDonald, G, I., and D. S. Andrews. 



In preparation. Variation patterns of single aeciospore cultures of Cronartium ribicola 

 (J. C. Fisher en Rabenh) . 

 Riker, A. J., T. F. Kauba, and B. W. Henry. 



1947. Tlie influence of temperature and humidity on the development of white pine blister 

 rust on Ribes leaves. Abs. Phytopath. 37:19. 

 Savile, D. B. 0. 



1953. Short-season adaptation in the rust fungi. Mycologia 45:75-87. 

 Snedecor, G. W. 



1956. Statistical methods applied to experiments in agriculture and biology. Laura State 

 Press, Ames. 

 Spaulding, P. 



1922. Investigations of the white-pine-blister rust. USDA Bull. 957. 

 Van Arsdel, E. P., A. J. Riker, and R. F. Patton. 



1956. The effects of temperature and moisture on the spread of white pine blister rust. 

 Phytopath. 46:307-318. 



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