Lehmann lovegrass (Eragrostis lehmanniana) is a species that despite the fact that being invasive is used in grasslands revegetation programs. However before of use it, is important to improve its livestock intake and with that reduce its invasiveness. The medium lethal dose (LD50) and growth reduction dose (GR50) are measurements used to determine proper radiation doses for plants genetic improvement programs conducted through mutagenesis. The objective of this study was to determinate the LD50 and the GR50 on lehmann lovegrass (Eragrostis lehmanniana).� The variables evaluated were germination percentage (GP), germination speed index (SGI), plumule length (PL), radicle length (RL), forage yield (FY), seed production (SP), stems number (SN), plant height (PH), tillering deiameter (TD) and chlorophyll concentration index (CCI). Data were analyzed through a trend analysis for each variable. With the resulting regression equation the LD50 were estimated based on GP and the GR50 based on SGI, PL, RL, FY, SP, SN, PH and CCI. In addition, data were analyzed through means comparison with the Dunnett�s test. Also, with the results obtained for LD50 and GR50 there a weighted average was calculated. Most of the variables evaluated did not show effects (P>0.05) under radiation exposures of doses lower than 1400 Gy. Moreover, germinated seeds that were exposed at 2000 Gy did not survive more than 21 days. The LD50 on lehmann lovegrass was found at 2076 Gy, while the GR50 ranged between 1357 and 1900 Gy. Therefore, for the genetic improvement of this species is recommended to use the weighted average obtained from both parameters, such average was found at 1533 Gy.
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