Optimal dose of gamma irradiation with 60Co for mutagenesis induction in grasses

Abstract

In plant breeding programs, the lethal dose (LD₅₀) and the median growth reduction (GR₅₀) are parameters used to determine appropriate irradiation doses to induce effective mutations. The objectives were to determine the LD₅₀ and GR₅₀ on seeds irradiated with cobalt 60 (⁶⁰Co) of blue grama (Bouteloua gracilis), sideoats grama (Bouteloua curtipendula), buffel grass (Pennisetum ciliare) and weeping lovegrass (Eragrostis curvula), as well as determine a weighted average of the LD₅₀ and GR₅₀. Seeds of these species were irradiated with Co⁶⁰ at seven different doses were evaluated. Doses intensities included: 0 (control, T-0), 100, 200, 300, 450, 600 and 900 Gray (Gy). The variables evaluated were germination percentage (%GE), speed germination index (IVG), plumule length (LP) and radicle length (LR). Regression analysis and means comparison with the Dunnett test were performed with the data. In addition, LD₅₀ was estimated through a regression equation on the data of %GE while the GR₅₀ was calculated with the reamaining variables. Moreover, a weighted average was calculated with the values obtained from both parameters. The LD₅₀ was weighted at 55%, while the GR₅₀ was weighted at 15% for each of the three remaining variables. In general, the values of all the response variables decreased (P<0.05) as the irradiation doses increased, which allowed the estimation of LD₅₀ and GR₅₀, for each species. The weighted average was obtained at 628 Gy, 712 Gy 698 Gy and 411 Gy for wepping lovegrass, buffel grass, sideoats grama and blue grama, respectively. We do recommend the use of these doses in plant breeding programs of these species.