BLISTER RUST RESISTANCE OF EASTERN KHITE PINE IN EUROPE 247 



Scholz (1960) stated that in fact a number of grafted plants had 

 died as the result of attack of the rootstock by C. ribicota. 



Scholz (I960) also reported on wound inoculations with aecidiospores 

 executed in June 1954, the spore material originating from three different 

 localities, Chorin, Colbitz and Waldsieversdorf . In February 1956 a 

 considerable amount of "old aecidia" were noticed. However, it is impor- 

 tant to mention that Scholz himself is not quite sure whether the results 

 were due to his inoculations or to "Fremdinfektionen" . Boyer (1964) 

 subsequently has reported his failure to secure inoculation of P. strobus 

 by viable aeciospores , with or without wounding. 



Meyer (1954) reported on 32 healthy P. strobus of about 40 years 

 age selected in the Odenwald Forest. These trees were carefully checked 

 for the presence of the rust by examination of the crown and side 

 branches. Scions were taken from these "healthy" trees in 1950/1951. 

 By spring 1954, it was demonstrated that 4 clones were susceptible to the 

 rust, whereas 2 other clones seemed suspicious. Meyer believes that, in 

 the near future, many more clones will prove to be non-resistant. 



In Denmark P. strobus and crosses between P. strobus and P. peuoe 

 Griseb. were tested for resistance to blister rust. The results of this 

 work will be reported in a separate paper to be given at this symposium 

 by Dr. B. S0egaard. 



Now and then incidental observations with regard to "resistance" in 

 older stands of eastern white pine have been made in various parts of 

 Europe. Schwend (1949), for example, reported on the occurrence of 

 healthy 7. stro'cy^ stands in the environs of KrakoV (Sanok and Lesko) , 

 a region from which the pathogen is well-known. 



DISCUSSION 



In view of further work to be done with regard to resistance research 

 in eastern white pine against the blister rust fungus, particularly when 

 applying grafting techniques, I would like to draw attention to the 

 importance of healthy rootstocks. Hhen using rootstocks from unknown 

 origin, a risk is taken that these already may be infected by the rust; 

 subsequently this may cause considerable confusion when estimating the 

 degree of resistance of the grafts, since infection of the rootstock may 

 lead to a die-back of the whole plant. Therefore rust-free rootstocks 

 are of basic importance. 



Another problem in developing resistant white pines is our present 

 lack of knowledge on the existence of physiological races of the fungus. 

 Much more detailed information on this subject is needed to supplement 

 the scanty information given by Anderson and French (1955) . 



In comparison with the abundant information on Melampsora rusts of 

 poplars (van Vloten, 1949) , data on possible races in the fungus C. 

 ribicola are just becoming available (see Hoff and McDonald, these 

 proceedings) . 



Further research by inoculation of Rices spp . leaves by various 

 rust provenances might be helpful in this work, using the leaf disc method 

 in petri-dishes developed during study of the Marssonina leaf blotch 

 disease in poplar (Gremmen, 1964). Moreoever, we need to study the 



