510 H. R. POWERS. JR, 



about gall formation or lack of gall formation. Dr. Dwinell who is here 

 with me from Athens, Georgia, has done some very interesting work with 

 the differences between C. querouum and C. fusi forme , especially on the 

 infection type on the oak alternate host, and it may be that we are 

 getting to the point you are making; something comparable with the wheat 

 rust infection types. Maybe we should look on the oak side of the picture. 



KAIS: I would like to make a comment here. I have studied isolates 

 of Cronartium fusiforme collected from different geographic areas and have 

 concluded that pathogenic variability occurs between geographic sources of 

 the fungus. We have detected these differences on a single progeny of 

 slash pine. 



COWLING: I'd like to ask both of the speakers about a suggestion Dr. 

 Callaham made during the coffee break. He suggested that a central 

 facility be formed to evaluate the progenies and selections of all of the 

 tree improvement programs of the south. Supposing that facility were 

 created, what would be your recommendations so far as inoculum is concerned? 

 Would you use both Cronartium fusiforme and C. querouum or would you use 

 mixed inoculum or what would be your recommendation? 



POWERS: I would suggest a specific known culture of C. fusiforme. 

 And if necessary let Dr. Dwinell check it out with his black oak response 

 to make sure you had what you thought you had, and use that to screen 

 routinely. We will undoubtedly continue to screen not on a mass basis, 

 but on a limited research basis with other specific isolates. For overall 

 screening, I think I'd select one known isolate of C. fusiforme 3 because 

 the C. querouum really isn't the problem that C. fusiforme is. 



KAIS: I agree. For economic reasons, we should use C. fusiforme 

 since C. querouum is relatively unimportant. 



CALLAHAM: Dr. Powers, you may be in conflict with what Kais just 

 said. Did you suggest using only a single isolate or a single geographic 

 source when he already has evidence of geographic variation in the species 

 and in its responses? Should we not start considering the interactions 

 among provenances of parasite and provenances of host? 



POWERS: Naturally, if you have two different races within C. 

 fusiforme, you need to screen with both. 



CALLAHAM: Do you have evidence of races of the rust within the 

 south, for example? 



KAIS: We have, yes, and it will be published. 



COWLING: Why don't you use a mixed inoculum? 



POWERS: I imagine you might cover up some possible sources of 

 resistance. 



COWLING: Would you not also avoid the mistake of having certain 

 progenies that are actually susceptible to fusiform rust appear to be 

 resistant? 



