nybom: vegetativelv propagated species 283 



The genotypical background might in such cases consist of losses of 

 large chromosome sections or other gross cytological changes, leading 

 to profound changes of skin properties, for example. This is probably 

 not a very rare example of variety improvement that would not easily, 

 or not at all, be attainable by ordinary cross breeding but only by 

 means of mutations, delimited to a special tissue of the plant. There 

 are thornless blackberry varieties, for example, which seem to give 

 rise to crippled dwarfs when tissue-homogeneous (26), and there are 

 variegated Pelargonium types which, under the same conditions, 

 either are practically lethal or not able to form any flowers (8). 



One could also well imagine that many ectochimaeric mutations 

 with retained acceptable characteristics of the deeper lying tissue 

 might not be usable as tissue-homogeneous clones because thev would 

 impair fruit quality, flesh color, and other properties. Again, the use 

 of somatic mutations offers quite unique possibilities perhaps some- 

 what hypothetical but indeed not unlikely. I might refer, for exam- 

 ple, to the negative correlation often found between quality and 

 disease resistance (21, 60). 



Use of Mutations in Relation to Other Breeding Methods 



After his review on radiation in the production of useful muta- 

 tions, Smith (104) arrives at the conclusion, "The crux of the problem 

 is — is it economically feasible to use radiations in plant improve- 

 ment? There is no one answer. . . the answers will be different depend- 

 ing on the material, objectives, and circumstances". 



I agree with this statement in all its details. The sometimes con- 

 tradictory and sweeping statements about the value of the mutation 

 method, or the irradiation method, must come from those who have 

 not understood that the mutation method, like any other single 

 method or tool in plant breeding, cannot possibly alone give us all 

 the completely new and improved varieties that we need and that 

 we are aiming at. The mutation method should be regarded as a 

 complement not an alternative to other plant breeding methods, 

 varietal crosses, species crosses, inbreeding, polyploidization, etc. 



We may observe that in some cases the mutation method has 

 indeed been "economically feasible". It has led to the production of 

 varieties that are paying for themselves. That it has indeed been an 

 "economical failure" in other cases is also evident. In addition to 



