PATHOGENIC VARIABILITY WITHIN FUSIFORM AND EASTERN GALL RUST 511 



DINUS: The nature of the data of which Kais is speaking is avail- 

 able in the recent Southern Conference on Forest Tree Improvement. Also, 

 I would like to make a plea that a much more detailed investigation of 

 this phenomenon be undertaken before any real suggestion is made as to 

 what to do about it, or before anybody actually makes a move toward trying 

 to set up a central testing facility. 



KINLOCH: It seems to me that you have got two distinct problems 

 here. If your objective is screening for production of resistant stock 

 to plant over a wide range of the host, then it seems desirable to 

 screen against the maximum genetic variation of the rust that you're 

 likely to encounter. Now, if you get host resistance after that you're 

 in pretty good shape for production. It does not answer whether racial 

 variation is present, however, when you're putting all the potential races 

 in an area into one inoculation. If you want to detect and prove the 

 existence of races you've got to start with genetically uniform inoculum. 

 If you're looking just for resistance in the host to any and all poten- 

 tial races then you get as many sources of inoculum together as you can. 

 The two problems are separate. 



POWERS: Dr. Kinloch, this gets back to Dr. Cowling's question. I 

 think you could do it either way, depending on your objective. I still 

 do not think, however, that I would mix C. quercuum and C. fusiform.e. 

 I think I'd stay with C. fusiforme. 



COWLING: I meant a mixed source of inoculum of C. fusiforme. 



POKERS: Oh, yes, possibly so. In any event I think I would not, 

 at this stage, bother with C. quercuum. 



CAMP AN A: I have the impression that C. fusi forme is much more 

 devastating in speed of killing the stem than is C. quercuum and I would 

 like to ask either one of the two speakers if this is an accurate impres- 

 sion, and if so, is this difference in pathogenicity related to the nature 

 of the gall, and any histological difference between tissues in the gall. 



POWERS: I think this is quite true. C. fusiforme is a much more 

 lethal rust. If you're going to get into the anatomy, could I refer you 

 to Dr. Frederick Jewell? He has done a great deal of work on the subject. 



JEWELL: The main tissue differences that show up are in the phloem. 

 With C. fusiforme , the phloem is much more disrupted and you don't get as 

 many sieve cells formed. With C. quercuum, you have a normal complement. 

 They are bent out of shape, true, but the transpiration stream is not 

 broken as it is in the slash pine with C. fusiforme. It's really disturbed 

 because they get all mixed up with parenchyma cells. While I'm here, I 

 would like to bring out another point. The question as to the specificity 

 of these two fungi has been raised many times. In other words, do we have 

 two separate species of fungi here or do we have one and a variation of 

 one? Dr. Powers' data showed they infect the same trees, and I was just 

 wondering if possibly we do have a race of C. quercuum and that happens 

 to be C. fusiforme. Bat that around for awhile. 



POWERS: We could spend half the day on that, I think, Dr. Jewell. 

 Arthur, in his manual of the rusts, did lump all of these pine-oak rusts 

 together, and this thing has been batted back and forth many times. We'd 

 have to have a discussion session on this alone. 



