352 



MUTATION AND PLANT BREEDING 



7T\ 



Figure 1. — X-ray-induced shift to sexuality i)i Poa pratensis. After Grazi, 

 et al. (32). 



in our efforts to improve our cultivated plants. An evolutionary sys- 

 tem based on mere addition of mutations under different selective 

 pressure would be a rigid and uneconomical mechanism of adjust- 

 ment to environment. Mutation breeding must be considered as one 

 method of approach, sometimes practically impossible, sometimes 

 inferior, sometimes insufficient but definitely promoting, and some- 

 times superior or the only solution. Its ability to furnish basic vari- 

 ability should not be considered as a substitute, but rather as a 

 complement to our world collections and other sources of natural 

 variation (47). 



Our skepticism and hesitation today can partly be referred to 

 the novelty of the method and to the feeling that nature should first 

 be exhausted of its resources, but partly also to our incomplete genet- 

 ic knowledge in relation to our specific breeding objects. The work 

 on maize and barley shows doubtless that a more profound knowledge 

 and a more systematic accumulation of gene and chromosome mark- 

 ers will greatly improve our chance to use mutation experiments in 

 plant breeding. In the collection of all these data and marker types, 



