Grain legume cultivars derived from induced mutations, and mutations affecting nodulation

Abstract

Two hundred and sixty-five grain legume cultivars developed usinginduced mutations have been released in 32 countries. A maximum numberof cultivars have been released in soybean (58), followed by commonbean (50), groundnut (44), pea (32) and mungbean (14). Gamma or x-ray exposures of seeds led to the direct development of 111 cultivars,while neutron and chemical mutagen treatments resulted in 8 and 36cultivars respectively. One hundred and three cultivars have been developedusing mutants in cross breeding. Attempts have been made to estimatethe successful dose range for gamma and x-rays, defined as the doserange, which led to the development, registration and release of a maximumnumber of mutant cultivars. Exposures to seeds ranging between 100-200 Gy in all grain legumes, except faba bean, resulted in 49 out of 111cultivars being developed as direct mutants. Successful doses reportedfor faba bean are lower than 100 Gy. Modified crop plant characters arelisted. Besides the development of new cultivars, a large number ofinduced mutants that show altered nodulation pattern have been isolatedin grain legumes. Such mutants have made a significant contribution inbasic studies on host-symbiont interactions and towards cloning of plantgenes related to symbiosis and nitrogen fixation. Their exploitation inbreeding programs for enhancing nitrogen fixation, is just beginning. Available information on nodulation mutants in grain legume crops issummarised. Mainly, four types of nodulation mutants have been isolated. They show either: no nodulation (nod -), few nodules (nod +/-), ineffectivenodulation (Fix-), hypernodulation (nod ++) or hypernodulation even inthe presence of otherwise inhibitory nitrate levels (nts). Hypernodulatingand nts mutants are of great interest. A soybean cultivar incorporating ntstrait has been released in Australia.