Present aspects of induced mutations in plant breeding

The present status of the utilization of induced mutations in plant breeding is briefly reviewed. It is concluded that with induced mutations in principle successes can be expected similar to those with the conventional breeding methods. Owing to the relatively small yield of progressive mutations the efficiency of mutation breeding, however, is rather poor at present. Greater efficiency may be expected with increased knowledge of both control of original mutation production and of selection.Control of mutation production seems to be possible in at least three ways, (a) by raising the total mutation frequency (b) by changing the relative frequency of chromosome versus point mutations and (c) by altering the spectrum of point mutations. The possibilities of such control through the diverse action of different radiations given with or without modifying agents is reviewed and various mutagenic chemicals are mentioned.Control of mutation selection may be achieved in two ways, (a) by a better understanding of diplontic selection (intrasomatic selection) of mutated cells and (b) by developing appropriate screening methods. A working hypothesis concerning the diplontic selection is briefly outlined. The one initial cell theory means that the greatest efficiency of mutation production can be expected after radiation of primordia or young buds with only one or a few initial cells which will form the tissue of interest. It is hoped that by this the intercellular competition is restricted and a reduced elimination of mutated cells will result.Procedures for selection of mutants, at least in barley, can already start with M₁-spikes. It was shown that completely fertile M₁-spikes possess the same frequency of point mutations (chlorophyll mutations) as those with disturbed fertility. Selection of fertile M₁-spikes should, therefore, eliminate to a large extent the undesirable chromosome mutations and in this way increase the efficiency of screening for progressive mutations. Maximum mutation frequencies of fertile M₁-spikes can, however, only be achieved if the tillering is reduced.It is suggested that more emphasis be put on screening of small mutations, which may generally be expected to have a greater importance for practical purposes than drastic deviations. Usually screening of micro vital-mutations will be advisable in the M₃-generation. Indicator characters may be found through mass selection methods which by their pleiotropic gene action also effect properties eventually of breeding value.Samenvatting Na een kort overzicht van de perspectieven voor toepassing van kunstmatige mutatie bij de plantenveredeling wordt nader ingegaan op enige problemen die thans de aandacht hebben. Voor het beheersen van de kunstmatige mutaties is het van veel belang de frequentie van mutatie te kunnen vergroten en te kunnen bevorderen dat relatief minder chromosoom- en meer gen-mutaties tot stand komen. Vooral van de micromutaties verwacht schrijver vooruitzichten voor de plantenveredeling. Het is echter thans nog zeer moeilijk daarop te selecteren.(Lecture delivered at the organizational meeting of the section Mutation and Polyploidy of EUCARPIA in Lund and Svalöf, July 9–11, 1958).