The Efficacy of Mutation Breeding 1 



WALTON C. GREGORY 



North Carolina Agricultural Experiment Station, Raleigh, N. C. 



It is the purpose of this paper to discuss some of the factors 

 expected to affect the efficacy of mutation breeding and to bring 

 forward data from which comparisons of efficacy may be drawn 

 between hybridization and mutation as methods of generating 

 genetic variance for purposes of selection. The paper will not be 

 concerned with the efficacy of various selection and screening pro- 

 cedures, it being considered that these, important as they are, are 

 by no means restricted to mutation breeding and, if improved, 

 would benefit any method of breeding. The discussion has mean- 

 ing in man's effort to create plant breeding capital in contrast to 

 the accepted methods of liquidating natural mutational assets 

 accumulated over evolutionary time. 



The basic questions are (a) whether the power of present known 

 mutagens is such as to produce the kinds of changes which natural 

 mutation and selection have provided us, and (b) given this power, 

 with what efficacy can it be used with plants of various breeding 

 structure? 



The Power of Mutagens 



There is reason to believe that despite the different frequen- 

 cies of similar mutations obtained with different mutagens (15, 

 14, 54), 2 the chief limiting factor in mutation production and 

 mutant recovery is the genie constitution of the experimental organ- 

 ism and not the type of mutagen used. Thus, for the plant breeder, 

 a knowledge of what might be called mutant expectation in his 

 material may be more important than a resolution of the mechanism 

 of mutational change at the submicroscopic level. 



Contribution from the Field Crops Department, North Carolina Agr. Exp. Sta., 

 Raleigh, N. C Published with the approval of the Director of Research as Paper No. 

 1253 of the Journal Series. This work was supported by the U. S. Atomic Energy Com- 

 mission as part of Contract AT-(40-l)-1747. 



2 See References, page 482. 



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