REPORT OF THE DEPARTMENT OF BOTANY. 



DOES CRONARTIUM RIBICOLA OVER- WINTER 



ON THE CURRANT?* 



F. C. STEWART and W. H. RANKIN. 



SUMMARY. 



Currant felt-rust and white pine blister-rust are caused by the 

 same fungus, Cronartium ribicola, in different stages of its life 

 cycle. On account of repeated outbreaks of felt-rust on currants 

 at Geneva unaccompanied, apparently, by the occurrence of blister- 

 rust on pines in the vicinity, it was suspected that, contrary to 

 accepted belief, the fungus may over-winter on currants. It is 

 important to know if this be true, because of its bearing on the 

 control of blister-rust. If true, the distribution of affected currant 

 plants must be prohibited; if not true, there is no necessity for 

 such restriction. 



An attempt was made to solve the problem by transplanting 

 diseased currant plants (after the leaves had fallen) into green- 

 houses and forcing them into growth during the winter. Through 

 the cooperation of four other plant pathologists it has been possible 

 to have such tests made in six greenhouses in as many widely 

 separated localities. In four of the greenhouses there were made, 

 also, attempts at inoculation by means of diseased currant leaves 

 which had been wintered out-of-doors. 



Although the total number of plants used in these experiments 

 was about 500 and every one of them had been severely attacked 

 by the felt-rust the previous autumn, no trace of Cronartium appeared 

 on the new leaves. This leads to the conclusion that C. ribicola 

 rarely, if ever, over-winters on currants. Hence, it is unnecessary 

 to quarantine currants affected with felt-rust. 



The recent discovery of two white pine trees affected with blister- 

 rust makes it possible, now, to account for the outbreaks of currant 

 felt-rust at Geneva without assuming that the fungus over-winters 

 on currants. 



*Reprint of Bulletin No. 374, February; for Popular Edition see p. 906. 



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