NILAN AND KONZAK: MUTATION INDUCTION EFFICIENCY 459 



than yield? In other words, the emphasis would be on different mutants 

 rather than repeats of the same mutant. Possibly yield and spectrum 

 are closely correlated. 



Nilan: Yes, as we have discussed in the paper we are very much inter- 

 ested in finding ways of altering the mutation spectrum and of directing 

 the induced mutation process toward specific desired changes. How- 

 ever, we think that increasing yield of many mutations in a genotype 

 is also very important. I am afraid we do not have enough information 

 yet to determine the relationship, if any, of yield and spectrum. 



Brawn: Albinos may be due to a variety of causes ranging from point 

 mutations to deletions of some size. Beneficial mutations are not likely 

 the result of deletions and so may differ in environment-treatment 

 response. What is the likelihood that the treatments you have used 

 may be specific for inducing only those mutants (albinos, etc.) which 

 you used as the criteria for measuring mutation rate? Are beneficial 

 mutants induced to the same degree and in the same way? 



Grobman: Doctor Brawn's question has relevance in regard to resolution 

 limits in the evaluation of different mutagens as to their effects in pro- 

 ducing variable mutation spectra. I am particularly disturbed with the 

 presentation in this paper and the preceding ones of chlorophyll muta- 

 tion data to substantiate differences in mutation spectra due to different 

 mutagens. The synthesis of chlorophylls in chloroplast grana is a very 

 complex biochemical process, conditioned by at least 20 environmental 

 factors, and in barley by at least 200 to 300 different genes, as it appears 

 to be evidenced by Swedish mutation work (and Doctor MacKey may 

 check me on this point). Scoring of chlorophyll mutations would, there- 

 fore, be a gross and inefficient manner of defining the limits of particular 

 mutagen-induced mutation spectra. Characters conditioned in their 

 phenotypic experssion by few genes, if selected, would give a much 

 finer resolution of mutation spectra, in studies where differences between 

 different mutagens were of primary interest. 



Nilan: On the basis of the high chlorophyll mutation frequencies from 

 diethyl sulfate, we have looked for morphological mutants in mature M 2 

 barley plants. Last summer high frequencies of these mutants were found. 

 This indicates, I believe, that there is a good correlation between the 

 chlorophyll and morphological mutants in barley. 



