216 MUTATION AND PLANT BREEDING 



significance of small mutations should be tested. The experience 

 with large mutations has shown that, besides their relative rarity, 

 only a very small fraction exerts a positive influence on yield. 



The chance of producing more or less large mutations with 

 higher yield is, however, a matter of fact which cannot be over- 

 looked. In Table 3 some examples are given in barley. There is no 



Table 3. — Some Examples of Barley Mutants with Well-established 



Higher Yielding Capacity. * 



Author 



HOFFMANN (57) 

 FROIER (24) 

 FROIER (24) 



SCHOLZ, pers. com., also (93, 96) 

 SCHOLZ, pers. com., also (93, 96) 

 SCHOLZ, pers. com., also (93, 96) 

 SCHOLZ, pers. com., also (93, 96) 

 SCHOLZ, pers. com., also (93, 96) 

 Early, W 3 4 107 GAUL 



Winter Barley 

 Early, 506 5 114 SCHOLZ pers. com., also (93) 



Early, 481 8 107 SCHOLZ pers. com., also (93) 



* Kernel yield of the mother line is taken as 100. 



doubt that the higher yield is well established because these figures 

 are based on drill tests with several replicates over a period of at 

 least 4 years. It should be noticed, however, that in these examples, 

 the higher yielding power is proved only for one location. 



The objection often raised as to why such mutants have not 

 been released as varieties is not valid. Under the conditions in 

 which they were produced, the total expenditure in cross-breeding 

 as compared with "mutation-breeding", may have been of the order 

 of 50:1, or even 500:1. It is not surprising that by the time the supe- 

 riority of these mutants was established, through conventional breed- 

 ing methods, new lines were developed which were superior even 

 to these "yield-mutants". Moreover, a great deal of those progres- 

 sive mutants reported in the past were just derived as a by-product 



