BREEDING RUST RESISTANT TREES : MODERATOR'S SUMMARY 629 



Carl Heimburger (these proceedings) has given an excellent summary 

 of his many years of work on intercrossing the American species Pinus 



- <-3 } P. monticola, P. lambertiana Dougl . , P. albicaulis Engelm. , and 

 P. flexilis James with the Asiatic species Pinus wallichiana^ P. parviflora 

 (including pentaphylld) , P. armandii, P. koraiensis and P. s-vbivica and 

 the European species Pinus peuce and P. cembra. Although he has reported 

 partial sterility, manifested by a lower cone set and lower set of full 

 seed per cone than in intraspecific crosses, he has nevertheless success- 

 fully made many new interspecific crosses which definitely open the door 

 to the diversification and enrichment of the gene pool for resistance to 

 the blister rust pathogen. 



In the course of these studies, he has also made two other dis- 

 coveries of great potential value to forest genetics. These include 

 (1) the discovery of a gene (or genes) in P. peuce for early flowering, 

 and (2) the discovery of a gene (or genes) in P. peuce for resistance 

 to the white pine weevil, Pissodes strobi Peck, one of the principal 

 enemies of P. stvobus. Both of these discoveries are of profound 

 potential importance to future pine breeding programs. 



The dominant gene for early flowering has been transferred to several 

 other species in crosses and generally reduced the period required for 

 abundant flowering from 25 years, the normal for P. strobus , to from 

 5 to 7 years in the hybrids. This great saving in time removes one of 

 the principal barriers that has confronted forest geneticists in the 

 past. J urge you to use such genes imaginatively and aggressively with- 

 out fear that early flowering automatically means early senescense. 

 Moreover, it is inevitable that we will be utilizing shorter cutting 

 cycles for all species in the future than we have in the past. Ke will 

 be less concerned about the growth rate of P. strdbus , P. monticola and 

 P. lambertiana beyond 80 years, for most cutting cycles with these 

 species will probably be of 60 to 80 years. 



Henry Gerhold now has the interesting challenge of producing an 

 improved P. stvobus with resistance to both weevil and blister rust. 

 He has the opportunity to first combine the weevil resistance of P. 

 peuce with that which is apparently already present in P. strobus , and 

 either simultaneously or subsequently combining the weevil resistance 

 with rust resistance. To achieve this objective close cooperation will 

 be required between entomologists, pathologists, and breeders. Effective 

 methods will be needed for screening large numbers of seedlings for 

 resistance to both weevil and rust. Whether an attempt is made to 

 develop lines which from the outset combine resistance to both pests, or 

 to develop lines with resistance to rust and others with resistance to 

 weevils and subsequently combine them through convergent crosses, will 

 probably depend largely upon whether or not there are lines of P. strobus 

 available now with a good usable level of rust resistance. If such lines 

 are not available then the latter approach is the only feasible one. 



