84 EVA FUCHS 



Zadoks, J. C. 1963. A case of race differentiation of brown rust on 

 mature plants of wheat. Neth. J. Plant Pathol. 69: 145-147. 



FLOOR DISCUSSION 



PERSON: Dr. Fuchs' talk made it clear that the identification of 

 races and the whole business of dealing with their variability in cereal 

 rusts is quite a big subject. It may be a blessing with the work that 

 you are about to undertake with the white pine blister rust if you find 

 it impossible to buy the idea of establishing physiological races. Are 

 there any questions for Dr. Fuchs? 



ZUFA: Should we try to continue to identify races of blister rust 

 on the basis of ribes and what would be the importance of such work in 

 our breeding of resistance to white pine bliter rust? 



FUCHS: I think that's one of the questions I can't answer. I 

 really don't know what you should do. Zadoks recommended something else, 

 so perhaps you stay as happy as you are now. But of course, with the 

 adaptability of the rusts, I think one day you will have to deal with 

 races. They will come up; however, that's more judgment than knowledge. 



ZADOKS. I will try to add a little bit. Your question was whether 

 one should start identifying races using ribes. I think that identifying 

 races using ribes would be completely feasible and that you would find 

 them if you looked for them. On the other hand, I'm not sure that looking 

 for races on ribes i s really relevant to your problem. We have some 

 information on this in annual crops. Let me cite a few. In oat crown 

 rust, there are two types of physiological specialization. One on the 

 pycnial host Rhamnus , and another one on the grain host. There are two 

 froms of physiologic specialization which are somewhat linked but not 

 completely. Another example is the Poa-Ranunculus complex which has been 

 analyzed by Gauman in a completely different approach from ours. There 

 are a great number of so-called micro-species of Uromyaes poae Rabh. 

 which cannot be distinguished on Poa, but which can be distinguished only 

 because their pycnial stage appears on the different species of Ramunoulus. 

 Now, whether this is micro-species or physiological races is a matter 

 of semantics, and what is important is that you get physiological 

 specialization on the pycnial host. This is possible, with little 

 physiologic specialization on a uredial host. So, there are a few 

 examples in the literature which indicate that there are two different 

 systems of physiologic specialization—one on the uredial host, and one 

 on the pycnial host, which may or may not be related. Usually they are 

 not . 



PAWUK: I think a few years ago there was a publication out of 

 Minnesota indicating physiological specialization on ribes from three 

 or four isolates of Cronartium vibiaola collected around the country. I 

 don't remember the details on it , I just remember reading it. But, I 

 think that they had tested a few species of ribes an d found that there 

 were some differences in symptoms. 



LOEGERING: Why don't you call on Harry Powers to say something 

 about that? * 



