238 MUTATION AND PLANT BREEDING 



Conclusions 



It has been shown that the induction of mutations offers a new 

 tool which is potentially able to make progress in plant breeding 

 similar to that obtained with conventional methods. Mutants can be 

 used directly to establish a new variety ("mutation breeding"). They 

 can also be used in cross-breeding and for special aims. Generally, the 

 use of mutants is time-saving as compared with the traditional 

 methods. 



However, the rate of progressive mutations and, hence, the 

 efficiency of mutation breeding has been low until now. At present, I 

 doubt, therefore, if generally this method is as useful and more eco- 

 nomical than cross-breeding when a given aim is to be reached. 



At present, the uses of mutants in cross-breeding seems to be 

 more promising than mutation breeding. In cross-breeding, mutants 

 may complement the natural gene resources. Particular interest 

 attaches to the possibility of removing the undesired pleiotropic 

 effects of a mutation in a new genetic background. 



To summarize, the significance and importance of mutations in 

 practical breeding now lies in their complementary use to the well- 

 established breeding methods. Increasing the efficiency of the muta- 

 tion technique can lead to a greater use of mutations in conjunction 

 with the conventional methods. 



It should be emphasized that any evaluation of mutation breed- 

 ing is speculative at the present time. Crucial evidence on compara- 

 tive efficiency of traditional cross-breeding versus breeding with muta- 

 tions is almost completely lacking. Strict utilization of mutations in 

 practical breeding programs has scarcely been attempted until very 

 recently. 



In appraising the efficiency of and in defense of breeding with 

 mutations one could challenge the followers of the traditional meth- 

 ods with the view that the efficacy of cross-breeding is not extremely 

 great either. Thus, Vettel (125), one of the most successful practical 

 breeders in Germany, recently reviewed 30 years of his experience in 

 cross-breeding with cereals. He gave a statistic of all crosses he has 

 made in wheat, barley, and oats, analyzing 5,045 different cross- 

 progenies. Only 0.3 per cent from these 5,045 F 2 populations resulted 

 in commercially used varieties. In an evaluation of this figure, one 

 has to realize that very much work of further selection and breeding 



