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FLOOR DISCUSSION 



KINLOCH: There seems to be one problem with induced mutations; that 

 of distinguishing between true mutations and an abnormal physiological 

 response to radiation or whatever mutagen you are using. True mutation 

 can't be proved until you are able to get flowering, seed, and subsequent 

 segregation ratios in the offspring. Another approach that has been used 

 very successfully in some plants, notably Arabidopsis thaliana Schur, is 

 inducing by chemical mutagens, mutations in the apical meristem of a 

 plant, and incorporating this mutation in subsequent divisions until it 

 gets into the germ line of flowers. This gives a valid basis for really 

 detecting whether you have a genetic mutation or just a physiologic 

 response. Do you have any comment on that? 



KEDHARNATH: I have no disagreement on what you have said, but I 

 would like to approach it in a different way. When you use pollen for 

 irradiation, you are dealing with a single cell in a sense, and you are 

 widening plant selection and also cutting down the genetics and time from 

 irradiation to scoring time. So, in pine breeding, pollen irradiation 

 has a particular advantage compared to seed irradiation. True, in a 

 cross-pollinated species there is no precise way of saying you have 

 created the variation. The only thing we can do is to compare this initial 

 population with the new population, and see whether we have increased the 

 variability. 



BLAIR: In your paper you state that most pines are open pollinated. 

 In almost every instance, we have hardly begun to realize how much varia- 

 tion we have, let alone begin to tap it. I don't see how we could 

 seriously consider using induced mutation in a situation like this until 

 we have gotten much farther along in trying to tap what variability we 

 do have. 



KEDHARNATH: My suggestion is only that this is an additional approach. 

 After selecting your plus trees, say you had 40 or 50 trees that you're 

 working with there is a certain amount of variability available within 

 those 50 trees. After general combining ability and all such experiments, 



