244 J. GREMMEN 



Since these results were very disappointing, we hesitated to con- 

 tinue along these lines. Nevertheless, early in 1966 our Station commenced 

 work in assembling a collection of white pine materials that were perhaps 

 better identified in respect to their blister rust resistance. These 

 materials were received as scions. They were grafted on 4-year-old, potted 

 P. strobus rootstocks in spring 1966, and were transplanted to the nursery 

 in 1967. They are now under observation by persons in two of our Forest 

 Research Station Sections (Pathology and Resistance Research and Forest 

 Genetics of Conifers) at Wageningen. New materials now under observation 

 are outlined in Table 2. 



OTHER EUROPEAN RESEARCH 



The kind of work done by van Vloten (1939, 1941) was also tackled 

 in Germany by several research workers. 



Rohmeder (cf. Lehmann , 1950/1951) mentioned that about the year 

 1940 seed from P. strobus originating from various localities in North 

 America, partly collected from single mother trees, had been received. 

 The 2- and 3-year-old plants obtained from them were afterwards inocu- 

 lated several times with C. ribicola spores and then transplanted in two 

 different plots, one close to NUrnberg, the other near Mtlnchen. Some 

 years later it appeared that none of these plants showed a "complete 

 immunity", although differenes in resistance were observed. Some of 

 these provenances showed a 2 to 4% loss by the rust , others up to 36% 

 during the first 10 years of observation. 



Again Rohmeder (1954) reported that in 1952 his Institute received 

 "durchgezllchtetes blasenrostresistentes Strobensaatgut aus der gelenkten 

 Kreuzung resistenter Pfropflinge" by courtesy of Dr. A. J. Riker and 

 Professor Dr. R. F. Patton. 



Dr. Patton informed me 1 that the seed sent to Dr. Rohmeder were 

 progenies of P. strobus selections that had proved to be resistant, to 

 varying degrees, by their responses to both artificial and natural inocu- 

 lations. The following progenies, to be called phenotypically resistant, 

 were sent: Nos . 36 x 38; 191 x 38; 312 x 38; 312 x 129, and 314 x 18. 

 Nos. 18, 36, 129 and 312 were rated as highly resistant; 38, 191 and 314 

 as having a moderate degree of resistance. 



Rohmeder stated later 2 that these seedlings were exposed to a severe, 

 natural infection as well as to artificial inoculation by means of spores 

 of the Cronartium fungus in the Experimental Garden at Grafrath. Later 

 on it appeared that all plants became heavily infected by the rust and 

 consequently the experiment was terminated. 



It is interesting to note that three of these progenies (36 x 38, 

 312 x 38, and 314 x 18) suffered a similar fate at Wageningen. 



In spring 1960, Rohmeder 2 received a number of scions originating 

 from 8 resistant P. strobus trees through the intermediary of Drs . Riker 

 and Patton. After successful grafting at Grafrath, the whole plot was 

 exposed to artificial and natural infection, the rust spreading from 



1 Personal communication } June 20, 1969. 



2 Personal communication, February 1Z, 1969. 



