BREEDING POPLARS RESISTANT TO DISEASE 607 



in your Table 1 which is individual culling level. Now, it seems to me 

 that you still could follow this approach of having three different 

 replications of the same full -sib family, one of which you expose at say 

 age 2 or 3. I leave that to the foresters. But somewhere along the line 

 you have to expose them. Then, in another group you expose the families 

 to the weevils at whatever age it is most tender. Then one can pick out 

 the various ones and mate them together. I am not sure if full-sib 

 mating will work out too well, but it does seem to me your individual 

 culling levels are the best scheme I have heard here. I'd have to look 

 at some data. I don't believe you have too much of this, do you? 



GERHOLD: No, not pertaining to weevil resistance. 



BECKER: Ke are trying to generate some for blister rust resistance 

 which you heard yesterday. It's not very easy. 



KRIEBEL: If you have extremely low frequencies of blister rust 

 resistant trees, 1 in 10,000 has been suggested and if the level of weevil 

 resistance was also 1 in 10,000, the number of individuals containing 

 both traits would be 1 in a hundred million. And when growth is added, 

 your chances of finding a tree that combined all of these traits is 

 infinitely small . 



