74 U.S. DEPT. OF AGRICULTURE MISC. PUB. 939 



The nonalternating race (Peridermium pint) has repeating aecia. 

 There may be some very small morphological differences between the 

 aecia of the host-alternating and those of the nonalternating race. 

 But even if there are slight differences, they are too small to serve as 

 distinctions between the two races. In Norway and Sweden, at any 

 rate, the nonalternating race is by far the most common. 



Resistance. — As to resistance, there is a considerable difference be- 

 tween individuals of Scots pine. The resistance has been proved to be 

 inheritable. 



Importance. — In Europe and Northern Asia Cronartium flaccidum 

 is one of the most important pathogens on two-needled pines, especially 

 Scots pine. Stands with a high percentage of killed or spike-topped 

 trees, as a result of attacks by this blister rust fungus, are not in- 

 frequent. 



Control. — Control measures are — 



1. Eradication of the alternate hosts 



2. Removal of infected trees 



3. Use of seed from resistant trees 



Potential threat. — We do not know which of the two-needled 

 pines may prove susceptible, but one or more of important American 

 species may be damaged if the host- alternating or the nonalternating 

 race should be spread to America. 



Range : Nearly all of Europe. Northern Asia to the Far East, Korea, 



and Japan. 

 Hosts: Pinaceae (section Diploxylon). Aecial hosts — 



Finns densiflora Sieb. & Zucc. 



P. halepensis Mill. 



P. mugo Turra. 



P. nigra Arn. 



P. pinaster Sol 



P. sylvestris L. (most important host) 

 Uredo and teleuto on many dicotyledonous genera in widely dif- 

 ferent families — 



Acanthaceae: Ruellia 



Asclepiadaceae : Asclepias, Cynanchum 



Balsaminaceae : Impatiens 



Gentianaceae : Gehtiana 



Loasaceae: Grammatocarpus, Loasa 



Ranunculaceae : Paeonia 



Solanaceae : Schizanthus 



Scrophulariaceae : Euphrasia, Melampyrum, Nemesia, Pedicularis 



Tropaeolaceae : Tropaeolum 



Verbenaceae: Verbena 

 Literature : 

 Gaumann, E. Die Rostpilze Mitteleuropas : 81-84. Bern. 1959. 

 Kuprevicz, V. T.. and Tranzschel, V. H. Flora plantarum crypto- 



gamarum USSR Vol. IV. Fungi (1). Uredinales. Fasc. 1. 



Familia Melampsoraceae : 261-265. Moscow, Leningrad. 1957. 



