kramer: discussion of session v 489 



of it. Evidence of recent origin for such specificity with respect to 

 response to mutagenic agents might have been anticipated and fur- 

 ther examples are bound to be forthcoming. This what still encour- 

 ages the hope and fosters the belief that a degree of control over the 

 type of locus which can be induced to mutate may yet be achieved. 

 This, in turn, should influence the type of variability that can accu- 

 mulate in populations. 



Doctor Gregory has emphasized the idea that the spectrum 

 of diversity of induced mutants which can be immediately recov- 

 ered from a given organism is a property of the organism itself 

 rather than a property of the mutagen used, and that this spectrum, 

 in turn, is governed by the evolutionary history of the organism. 

 Initial experience with induced mutations with a variety of organ- 

 isms certainly confirms this view but has led in some instances to 

 questions about the efficacy of mutation induction as a tool in plant 

 breeding. 



On the other hand, this view must necessarily be a temporary 

 one if the idea is accepted that the purpose of mutation induction 

 is to accelerate change. Under such accelerated change, accumu- 

 lated variability might, in turn, be expected to widen the bound- 

 aries or raise the ceiling for new variability in an ever-accelerated 

 cycle in which genetic variability must inevitably eventually become 

 divorced from evolutionary history. The tools are available for such 

 an approach. 



Herein, it would seem, lies the importance of the work report- 

 ed by Nilan and Konzak and by Caldecott on increasing the dose 

 tolerances and induced mutation yield, and by Caldecott on the 

 effect of recurrent treatments. It seems reasonable to expect that 

 the coincident quantitative variation so effectively demonstrated by 

 Gregory and his students and coworkers would naturally increase 

 along with the more easily measured yield of qualitative mutants. 



Attempts to decide whether "mutation breeding" (perhaps 

 unfortunately coined) is or is not applicable to a given species are 

 too often colored by the immediately foreseeable and sometimes 

 limited objectives of a breeding program. Who can say what breed- 

 ing objectives for a specific crop will be 50 years hence? Plant 

 breeders are often so restricted by prejudices that hinder accept- 

 ance of new products that they must operate within relatively nar- 



