38 



WILLIAM Q. LOEGERING 



FLOOR DISCUSSION 



BINGHAM: Dr. Loegering, why can we not identify a race in blister 

 rust by simply passing it back through the ribes and continue a genetic 

 analysis thereafter? 



LOEGERING: The answer to your question involves a definition for 

 the word race. Races are identified on specificities and colonal propa- 

 gation of host and pathogen or non-segregating populations are necessary. 

 Now, if you can produce a non-segregating line--for instance if your 

 pathogen is homothallic as has been suggested here, and by some of your 

 work, then this homothallism can be used in this respect. Also, you 

 could demonstrate specific races by grafting or with tissue cultures by 

 using them for inoculum since they are clones. You must be able to 

 inoculate two different plants with the same sporidium somehow or another. 

 If your pathogen is homozygous then you have no segregation and this can 

 be used as you suggest. There are several men who are working on the 

 smuts here today. Their concept of a race in smuts is so different from 

 that for the cereal rusts that it is hard for us to communicate. The 

 point that I would make, however, in all of this is that in blister rust 

 forget about races and use the genes instead of the race concept. I 

 would jump the race bridge. I wouldn't monkey with it. 



GERHOLD: 

 no infection? 



Dr. Loegering, in your model does low infection includ< 



LOEGERING: No, because an aegricorpus is what you use to determine 

 these things and if you have no infection you have no aegricorpus. 



GERHOLD: Can the condition of no infection be incorporated in the 

 concept then? 



LOEGERING: No, because you have no disease if you don't have a 

 pathogen. If we have a pine tree growing out here and there are no ribes 

 and no sporidia around then you should not include this in the disease 

 concept. Escape, which you are dealing with here, is another thing. It 

 has nothing to do with the gene-for-gene relationship. 



GERHOLD: I didn't want to include escape here but I did want to 

 refer to a possibility of a gene whicn would confer immunity. How do 

 we deal with this? 



LOEGERING: I, first of all, would ask you to define what you mean 

 by immunity because I do not believe that such a thing exists. 



PERSON: May I interrupt here? 



LOEGERING: Go ahead. 



PERSON: I think the question concerned a gene that conferred resis- 

 tance because it prevented the fungus from infecting the host. 



LOEGERING: Then you are dealing with something like klenducity, for 

 example escape, because the pine trees have wax on the needles or some- 

 thing of tnis type. This might be the result of a single gene but this 

 would be universal and I am quite sure I would include it under non- 

 specificity. Dr. Zadoks, would you want to comment on the separation 

 here of ideas on general resistance? 



