Evaluation and genetic analysis of semi-dwarf mutants of wheat

Large numbers of semi-dwarf (reduced height) mutants have been recovered over the 20 years we have been inducing mutations. Because of our need to emphasize practical breeding goals, few of the mutants have yet been subjected to genetic analyses. Efforts to modify and improve some of the mutant semi-dwarf plant types for use in breeding are continuing, as are experiments to induce new reduced height mutants in advanced breeding lines. Radiation induced mutant, Burt M 937 (CI 15076) carries a recessive reduced height gene designated rht4. Gene rht4 is independent of Rht1 and Rht2 of spontaneous origin. EMS mutant Marfed M 1 (CI 13988) carries a partially dominant gene designated Rht5. The spontaneous recessive gene rht6 present in the 'short standard' cultivar Burt (CI 12696) was designated to clarify the genetics of height control in the Burt background relative to a taller form (Itana). Gene Rht7 has been designated from studies by others. The relation of rht4, Rht5, rht6 and Rht7 is yet unknown. Our recent research indicates that a single partially dominant reduced height gene in mutant Magnif 41 M 1 (CI 17689), and the possibly completely dominant reduced height gene present in mutant Karcag 522 M 7K merit early identification in the wheat genome because of their promise for breeding. These mutant genes represent a significant addition to the previously known germ plasm resources for reduced height in wheats. A coordinated, international effort is needed to expedite genetic analyses, identification and breeding evaluation of the large numbers of reduced height mutants even now available. Cooperative interchange of potentially useful stocks and information about them will stimulate breeders to employ promising induced mutants to complement or supplement spontaneous reduced height gene sources, thus reducing genetic vulnerability of wheat, the world's most important cereal crop. (author)