gall: induced mutants in seed-propagated species 215 



of one of the multiple genes concerned. Indeed the results obtained 

 in Drosophila (63, 97, 120) and peanuts (39, 41, 42) suggest that 

 the frequency of small mutations is considerably higher than that of 

 large mutations. 



Methods of Breeding with Mutations 



Mutants can be utilized in various ways in plant breeding 

 and the most important methods are reviewed in Table 2. The term 

 "mutation breeding" is often loosely used. In the classification of 

 Table 2, it is suggested that the term mutation breeding be used 

 only when a new variety results from the direct propagation of 

 the mutant. Extensive use of mutants can be made in the various 

 methods of cross-breeding. Besides, there are a number of special 

 aims for which mutagens may prove valuable, and these are outlined 

 in Table 2. 



Table 2. — Methods of Breeding with Mutations and Use of Mutagenic Agent 



in Seed-propagated Species. 



A. Self-pollinating species mainly 



1. Immediate use of mutants: Mutation breeding proper 



2. Use of mutants in cross-breeding 



a. Within the same variety 



b. With foreign varieties 



c. In hybrid populations, as an additional source of variability 



d. In heterosis-breeding (including cross-pollinating species) 



B. Cress-pollinating species 



3. Induction of mutations in cross-pollinating populations 



C. Self- and cross-pollinating species 



4. Mutagenic agents as a tool for special purposes 



a. Induction of translocations for interspecific or intergeneric transfer of desired char- 

 acters 



b. Diploidization of artificially produced polyploids 



c. Use of translocations (with localized breakage points) for "directed" duplications 



d. Use of radiation to induce transitory sexuality in apomicts 



e. Use of radiation to produce haploids 



f. Use of radiation to break incompatibility in distant crosses 



Mutation Breeding 



The direct use of mutants offers theoretically the greatest 

 advantage in utilizing mutations in plant breeding. As compared 

 with cross-breeding, it may save nearly half of the time necessary 

 to create a new variety. Evidently here lies the field in which the 



