STEPHENS: RESUME OF THE SYMPOSIUM 509 



in conventional breeding;. Recombination between nonhomologous 

 genomes becomes practically feasible when irradiation is combined 

 with conventional cytogenetic techniques, as Sears has shown. It 

 may be possible to break cross-incompatibility barriers by gamete 

 irradiation as suggested by MacKey. These and other possibilities 

 share the requirement that an experience with mutagenic tech- 

 niques be combined with a knowledge of the cytogenetics and 

 breeding potential of the material under investigation. 



From these, still early, indications it would appear likely that 

 a distinction between mutation breeding and conventional breed- 

 ing is only a transitory phase in the development of both. In my 

 opinion their delayed incorporation is in large part due to the fact 

 that mutation breeding has developed as a by-product of "muta- 

 genic exercises". These tend to concentrate on the immediate pro- 

 duction of novel morphological deviants and to neglect the possi- 

 bilities of recombination among apparently normal segregates in 

 subsequent generations. Yet the successful manipulation of recom- 

 bination is a keystone in practical breeding. 



