450 



MUTATION AND PLANT BREEDING 



Table 3. — Comparison of Mutation Spectra Induced by Diethyl Sulfate 



and Gamma Radiation. 



to chemical treatment has been obtained from the experiments of 

 Westergaard and his associates with back mutations with Xeuro- 

 spora (40). 



Investigations Related to Appearance, Detection, 

 and Selection of Induced Mutations 



Several other approaches to greater efficiency and to increased 

 economic feasibility of artificial mutagenesis in plant breeding 

 should be explored more intensely. These include (a) the use 6f 

 pollen, zygotes, and embryos in mutation induction; (b) diploid- 

 ization of loci in polyploids by mutagen treatment; (c) alteration 

 of reproductive mechanisms, especially self-incompatibility and 

 apomixis, by mutagen treatment; and (d) development of efficient 

 recurrent mutagen treatment techniques. Most of these are con- 

 cerned with the appearance, detection, and selection of mutations 

 rather than with the induction of mutations per se. However, they 

 will be considered briefly here since progress along these lines can 

 extend the usefulness of mutagen techniques. 



Irradiation of Pollen, Zygotes, and Embryos 



Most mutation breeding experiments have been initiated either 

 with seeds of sexually propagated crops or with buds of cuttings in 

 vegetatively propagated plants. However, both seeds and buds are 

 multi-cellular, complex tissues presenting certain difficulties for 

 induced mutation detection and selection. These difficulties relate 



