234 



BENT F. S0EGAARD 



INTRODUCTION 



Pinus strobus L. was the most important of the 11 native and intro- 

 duced 5-needled pine species tried in Europe. From its introduction 

 early in the 17th century until blister rust stopped it in the late 

 1800' s, this tree was valuable for European conditions. My purpose here 

 is to evaluate this tree and each of the 10 other native and introduced 

 species for their resistance to attack by the fungus Cronartium ribiaola 

 J.C. Fisch. ex Rabenh. The species will be divided into three groups: 

 Native white pines (European white pines) ; white pines introduced from 

 Asia; and white pines introduced from North America. 



NATIVE WHITE PINES (EUROPEAN WHITE PINES) 



PINUS CEMBRA L. 



Pinus cembra was the original host for C. ribiaola, which was 

 discovered in 1854 by Dietrich (1856) in Estonia on Ribes nigrum L. and 

 other Ribes species, and also on Pinus strobus. He named the fungus C. 

 ribicola without any description. In 1872, J. C. Fischer made a short 

 description of the fungus also using the name C. ribiaola. Klebahn 

 (1888) was the first to show the identification between Peridermium strobi 

 Kleb. and C. ribiaola. P. cembra is attacked in its native area in high 

 elevations in the Alps and the Carpathian Mountains. Pinus sibiriaa 

 Du Tour is attacked in its native area in western and central Siberia to 

 northern Mongolia with isolated occurrences on the Kola Peninsula. The 

 attack often is not conspicuous as the tree possesses a high degree of 

 resistance. In the Piedmont Alps in Italy with R. alpinum L. nearby, all 

 the trees were attacked; but these were only branch infections, so some 

 sort of resistance apparently was present. No trees were killed (Gremmen, 

 personal communication). In the Botanical Garden in Hann. MUnden, the 

 attack on P. cembra was small as compared with P. strobus, P. lambertiana 

 Dougl., P. flexilis James, P. monticola Dougl., and P. aembroid.es Zucc . , 

 whereas P. strobus x P. griffithii McClell. (P. griffithii McClell is 

 synonymous with P. wallichiana A.B. Jacks.), P. peuce Griseb. and P. 

 griffithii were not infected (Meyer, 1954) . In Denmark in the Forest 

 Botanical Garden, P. cembra has been grown since about 1890 and no infec- 

 tions have been observed. It is also recorded in Belgium, Finland, France, 

 Great Britain, Norway, Poland, and Sweden (Buchanan, 1964). 



PINUS PEUCE 



Native to Albania, Yugoslavia, Bulgaria, and northern Greece, P. 

 peuce possesses a high degree of resistance although it can be attacked 

 by the fungus. P. peuce was infected to the same extent as P. strobus 

 in an experimental area in Schleswig-Holstein (Schenck, 1939). Crosses 

 with P. strobus (S. 873-45) made in Denmark in 1945 show that P. peuce 

 transfers its resistance quality to its offspring. Open pollinated 

 (S. 874-45) offspring of the hybrid P. strobus x P. peuce shows the same 

 tendency. The graphs in Fig. 1 through 4 illustrate the mode of resis- 

 tance that is transferred to the offsprings. Figures 1 and 2 show the 

 course of infection for 16 years from two seed collections of P. strobus 

 (S. 867-45 and S. 863-45). No individuals are alive after 16 years. 



