mac key: induced mutation in crop improvement 337 



the progressive value of induced mutation if proper precautions are 

 taken. If we now believe in a more balanced, more subtly differenti- 

 ated, and a more dynamic evolution, such proofs will, however, be 

 insufficient to rate mutation experiments as an ingredient in plant 

 breeding. The meagre data available on induced mutation in quanti- 

 tative traits and on the combining ability of induced mutations make 

 it very difficult completely to understand the evolutionary implica- 

 tion of artificial mutation. The very promising results obtained in 

 the sparse experiments along these two lines (2, 3, 17, 33, 34, 37, 76, 

 81, 91, 92, 104, 106), however, seem to justify more optimism. 



Our deficient knowledge of how to utilize mutation in crop 

 improvement must be borne in mind when we try to evaluate muta- 

 tion experiments as a technique in plant breeding. It seems very 

 likely that mutation work in the future will be more completely in- 

 terwoven with the so-called conventional methods, with which it now 

 too often is set in opposition. We have also to recall that most of the 

 mutation experiments done so far have been biased by theoretical 

 considerations and not planned as strict breeding projects. 



In addition, our knowledge of the relation between genotype 

 and the possibility of inducing progressive mutations is most meagre. 

 Nearly all our efforts have been concentrated on methods to increase 

 mutation rate and to find mutagens with a specific and effective mode 

 of action. For a plant breeder, it seems just as important to explore 

 the specific response of genotype to mutation, since the careful choice 

 of parental material is perhaps the most decisive part of the program. 

 Not even the most clever and observant handling can compensate 

 for unsuitable material. 



Table 1 lists some of the more important factors influencing the 

 genotypic response to progressive mutation. Available information is 

 too scant on many points to allow me to present more than self- 

 evident items of knowledge in this paper, and some of the problems 

 will be taken up by other participants in this symposium. For these 

 reasons, I will discuss only some factors related to the choice of 

 parental material which may be important for progressive mutation. 



From this special point of view, inherent mutagenic resistance 

 with respect to survival is only indirectly important as long as it influ- 

 ences the total yield of mutations. Drastic interspecific differences in 

 radio-resistance have been demonstrated in connection with both 



