The mediun lethal dose (LD50) and growth reduction (GR50) are measurements used to select appropriate irradiation doses to induce mutations in plant breeding programs. The objective of this study was to determine the LD50 and GR50 in blue grama (Bouteloua gracilis), sideoats grama (Bouteloua curtipendula), Buffel grass (Pennisetum ciliare) and weeping lovegrass (Eragrostis curvula). For that, seven irradiation doses over the seed were evaluated and included 0 (T-0), 100, 200, 300, 450, 600 and 900 Gray (Gy). The variables evaluated were germination percentage (% GE), germination rate index (GRI), plumule length (PL) and radicle length (RL). Data were analyzed using the GLM procedure available in the SAS software through trend analysis and comparison of means with the Dunnett's test. The % GE, GRI, PL and RL of sideoats grama, weeping lovegrass and buffel grass decreased (P <0.05) as the radiation dose increased. However, GE %, GRI and LP of blue grama showed an increase (P <0.05) at doses of 100, 200 and 300 Gy. In weeping lovegrass LD50 was estimated to be at 565 Gy, while the GR50 ranged from 490 to 867 Gy. In buffel grass LD50 was found to be 625 Gy and GR50 varied between 542 and 985 Gy. The LD50 in sideoats grama was found at 443 Gy, while its GR50 fluctuated between 406 and 1248 Gy. In blue grama LD50 was obtained at 398 Gy and GR50 ranged from 323 to 447 Gy. In these species, the doses between 100 and 300 Gy of gamma radiation can stimulate the capacity and speed of germination and plumule development.
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