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Abstract SField experiments was: conducted a t Sakha A gr iculture Research Station Farm a t Xafr El-Sheikh to study the effect of gamm-reys and ethyl methanesulphonate (Eim) each single and in combinations on M1, Id2 snd %generations (1975, 1976 and 1977) of two v a r i e t i e s of soybean, Clark and Hampton. The doses 0, 2.5, 5, 10, 15, 20 and 25 KR of gamma-rays were given, then the irradiated seeds were soaked in different concentretions of EM$, 0, 0.04, 0.06, 0.08 and 0.10%~ of EMS wexe used. A 1 1 possible combinations of gamma-ray doses and EXS concen fxations were employed, except the doses 20 and 25 KR of gamma-rays, which were used separately . The results could be summarized as follov~s :- 1- Plant height as well as number of pods, seeds and seed yield per plant in MI reduced consistently with the increase of both mutagen doses and combination levels, in both v a r i e t i e s . 2- Stirnulatory effect was ~pparently a t low doses of gamma-rays , EiMS and low levels of their combinat ions, where an increase over the controls of such characters was observed, in both varieties . 3- The number of branches ptr plant wrs s l i g h t l y affec~ ted by single or combined txectments in Clark, but a significantly decrerse than the control of H,mpton vms recorded a t high nutagen doses (20, 25 KR of gamrile-rays and 0.06, 0.08% of EIG) and af a l l levels of combination. :!loreover, an additive effect was found a t high levels of conbination, (15 KR+O.O6% and 15 KR+O. 10%) , 4- Concerning to 100-seed weizht , a signif icent increase was reported at higher doses of garnm-rays (20 and 25 KR) in both v a r i e t i e s , and a t high concentrations of both mutagens (15 ~R+0.08% and 15 KR+O.10%) in Hzmpton. 5- M1-fertility was highly signif icsnt decresse with increasing gamma-ray doses, E14S concentretions and the combinations of both, in two studied mrieties, In addition, EMS gave more stronger effect than gammarays and Hampton was more sensitive than Clzrk i n t h i s aspect . |