26 JOHN W. DUFFIELD 



FLOOR DISCUSSION 



BINGHAM: Dr. Duffield, while you were discussing monocultures and 

 their problems, it occurred to me that there are several blister rust 

 resistance breeders in the audience who are faced with one sort of mono- 

 culture problem at this moment. Gerald Barnes who is working in the 

 Forest Service, Region 6, white pine blister rust resistance program at 

 Cottage Grove, Oregon, and Dr. Bohun Kinloch and Gaylord Parks who are 

 cooperating in a similar Region 5 program in northern California have 

 recently, tentatively identified single (dominant) , major resistance 

 genes in Oregon Pinus montieola and Pinus lambertiana Dougl . (Region 6) 

 and California P. lambertiana (Region 5) . I would like to hear some 

 remarks by these men on how they intend to use this single dominant gene, 

 avoiding "monoculture" problems of the type associated with such single, 

 immunity-imparting genes. 



DUFFIELD: I suspect the question will carom off the panel; at least 

 I hope it will. 



KINLOCH: The finding Mr. Bingham mentions is recent. We're pretty 

 sure the mechanism of inheritance is simple but still don't consider our 

 findings conclusive. As far as the utility of this gene (or other genes 

 that express the same phenotype) is concerned in relation to different 

 pathogenic races of Cvonartium vibicola, I think the critical need now 

 is to test them in different regions which may harbor different pathogenic 

 races. This should be done repeatedly and over a period of time. The 

 gene or genes should be tested in different combinations, within the 

 species P. lambertiana and perhaps also with other species such as P. 

 stvobus to see if their behavior is the same as what we have observed 

 under natural infection in California, or what Mr. Barnes and coworkers 

 have observed under artificial inoculation in Oregon. The origin of this 

 gene is of some interest. It just sort of showed up and I think we were 

 all quite surprised. Perhaps as Dr. Borlaug and I were discussing yes- 

 terday it is a sort of a fossil gene, lingering in some parts of the host 

 population. This relates to Dr. Duffield 's remarks just a few minutes 

 ago. Perhaps some of the North American white pines carried with them 

 some major genes for resistance when they migrated from Asia. That's 

 just one speculation. Now, whether there are races of the pathogen 

 presently existing that are also carrying genes for virulence against 

 these, is just a question that we have to answer by repeated tests over 

 a range of geographic locations that may possibly harbor such races. 



LOEGERING: The use of the expression major genes is not good. When 

 we deal with major genes we find that some of these don't survive in 

 cereal crops. A good example was Bowie wheat. On the other hand, if we 

 go to barley, we have a major gene for resistance to Puooinia graminis 

 f.sp. tritici that has survived as long as it has been known, which is 30 

 to 40 years. There is no evidence that the pathogen has picked up the 

 virulence for this gene. Thus a major gene should not be discarded 

 because there is potential for it to go out next week, but neither should 

 it be accepted as something that is going to live with us forever. There's 

 another side to this. Many of you know that I have been involved in the 

 International Rust Nursery program, and I have a little experience that 

 may be of value here. Say Dr. Pope introduced a variety of wheat that 

 is resistant; it is resistant here in Idaho and we can't deny this. And 

 yet that same variety taken across the mountains may be susceptible--the 

 gene for virulence might be there. On the other hand this variety may 

 be resistant throughout North America, or you may find that no place in 



