GAUL: INDUCED MUTANTS IN SEED-PROPAGATED SPECIES 229 



selected, at least in the beginning, by eye inspection. With small muta- 

 tions, the basic phenotype is often not changed; and under these 

 conditions it is hard, if not impossible, to detect, for instance, an 

 increase in the yield potential of 5 to 10 per cent by simple eye 

 inspection. There is a need to develop mass selection methods, and 

 these will be different for different purposes and plants. This demand 

 is shared with conventional breeding methods, and indeed many of 

 the known selection methods can be applied to mutants in a more 

 or less modified way. There are, however, some basic differences 

 between conventional breeding and breeding with mutations, and 

 these will often require a different approach and special selection 

 techniques. It is not possible to go into more detail here on this 

 problem. 



For the selection of useful mutants, particularly of higher yield- 

 ing mutants, it might be possible to utilize the pleiotropic gene action 

 which seems to be connected with every (or nearly every) mutation. 

 I have suggested that one looks for "indicator characters" (25, 28). 

 These should be mutations which are relatively easy to detect, either 

 in a "normal" environment or under extremely changed (laboratory) 

 conditions. They are characterized by morphological or physiological 

 deviations which do not necessarily have breeding value. As a conse- 

 quence of the pleiotropy, a certain proportion of these mutants may 

 possess progressive features, i.e., they may have a greater yielding 

 potential. 



Selection of Mutants — Special Results 



We have started preliminary studies along this line in our labo- 

 ratory. Among various such indicator mutations we have considered, 

 the earliness character appears to be suggestive. Because earliness is a 

 polyfactorial character, the probability of a mutation-event is relative- 

 ly great; and earliness mutations have been frequently met with in all 

 species. Moreover, it is possible to recognize even small differences 

 with regard to the beginning of flowering. In cereals, the date of head- 

 ing is a character that can be recorded fairly precisely and small 

 differences become evident. In order to recognize small genetic differ- 

 ences, it is however necessary (a) to have a great number of plants, 

 (b) to work with replications, (c) to observe the material at least once 

 a day during the heading time, and (d) to observe the material for 

 several years. 



