566 HANS H. HATTEMER 



FLOOR DISCUSSION 



BINGHAM: May I try to reply, Hans, although I don't think I have 

 any sort of complete answer. Are your questions aimed at field testing 

 of the types that are there, and whether or not a different level of 

 resistance persists? 



HATTEMER: There was some talk about the difference in the general 

 level of resistance between unselected and selected material, and there 

 exists also some information upon the decrease of vulnerability with 

 increasing age. Starting with the percentages we were told about 

 yesterday afternoon, what further losses do you expect if you outplant 

 this material into the field? I suppose the general level achieved so 

 far is really close to the goal of the first step in selection for 

 resistance before you take account of other characters. 



BINGHAM: I would answer by saying that in the particular experiment 

 at which we looked the level of inoculation there imposed was low. Perhaps 

 it was more equivalent to field conditions than some experiments that 

 were more heavily inoculated, for instance, those on the table that I 

 handed out the other day. However, the only evidence we have that is of 

 any consequence is that in our initial experiments, we outplanted trees 

 directly to field plots. After 3 to 5 years on the field plots, trees 

 surviving 1 or 2 artificial inoculations, plus 3 to 5 years exposure to 

 fairly heavy natural inoculation from planted Ribes , were selected and 

 potted. These trees were all run back through the artificial inoculation 

 chambers before they went to the breeding arboretum where we store our 

 long-range breeding materials. While we did manage to inoculate a certain 

 proportion of these selected trees, most of them also survived artificial 

 inoculation at ages 5-7. Also we gained back another increment of 

 resistance, usually in bark types, which had not had a chance to express 

 themselves previously. So it would seem that we can maintain this 25 to 

 30% level through 7 years at least. We simply haven't been able to 

 manufacture enough of the Fi's to get them out for real field testing; 

 however, they are in the nursery and the first planting will go in next 

 year. 



BLAIR: You mentioned something about inbreeding. I would like to 

 ask if you or Dr. Stern would express any concern about going to a very 

 small number of clones in an orchard, say four or five clones, as an 

 intermediate measure in trying to get disease-resistant planting stock 

 into the field. Would this, you feel, be an unwise step, assuming that 

 we could get some resistance going this way? 



HATTEMER; I was not thinking of a seed orchard but of controlled 

 breeding work. In a seed orchard, you are never sure what really 

 happens. 



BLAIR: You must accept some of the inbreeding in the case where 

 you have a small number of clones in a seed orchard, even though you 

 don't know how much you are getting. Would you be concerned about it? 



HATTEMER: I was referring to the particular situation that the 

 project leaders are in. Parts of the distribution range were lost. So 

 one has to do something, and inbreeding will occur anyway in nature, if 

 man does not start planned breeding work. 



