gaul: induced mutants in seed-propagated species 223 



progressive mutants. The final output of mutants for plant breed- 

 ing depends on both the methods of original induction and of selec- 

 tion. According to the arrangement of Table 4, I have recently 



Table 4. — Possibilities of Obtaining a Higher Yield of Mutants for use in 



Plant Breeding. 



A. Control of induction 



1 . Through raising of mutation rate per surviving Mi plants 



2. Through alteration of the proportion of chromosome mutations vs. factor mutations 



3. Through alteration of the mutation spectrum 



B. Control of selection 



1. Through knowledge of chimera formation and diplontic selection in Mj plants 



2. Through improved screening methods of mutants 



reviewed the progress in obtaining more efficient production meth- 

 ods of mutants (28). The arrangement of Table 4 will also be the 

 basis of the following considerations. 



Induction of Mutations 



There is no need to review the subject of a control of mutation 

 induction again in detail, though in the meantime some remarkable 

 results have been obtained (13, 46, 67, 75, 76, 77). Such a limited 

 control appears to be possible through the different actions of the 

 great number of known physical and chemical mutagens that can 

 be used either alone or in combination with various secondary 

 factors. Also the stage of the plant development and the parts of the 

 plant being treated are important. 



Mutation research is in a stage of rapid development, and the 

 theoretical progress is fascinating in the fields outlined under Al 

 to A3 of Table 4. Yet, its practical application relative to "recipes" 

 for useful techniques in plant breeding is still limited. With regard 

 to the theoretical progress, I am, however, inclined to suppose that 

 methods to obtain a greater total mutation frequency (Table 4, Al) 

 will be available for everybody in the near future. I also would like 

 to speculate that techniques for a certain control of the relative fre- 

 quency of chromosome mutations vs. factor mutations (Table 4, 

 A2) will be developed in, say, the next 5 to 15 years. Alteration of 

 the mutation spectrum (Table 4, A3) is most apart from being 

 used in practical plant breeding. Up to date, conclusive evidence in 

 this field has only been obtained with chlorophyll mutations (cf. 28). 



