Glyphosate Influence on Growth and Nodulation of Glyphosate Resistant Soybean Cultivars

Glyphosate resistant soybean (GR) is a new technological tool in weed management applied in soybean culture, which accounts for the largest area planted in Brazil. Since it has been only recently applied in Brazil and abroad, further studies are needed to search for useful information on the correct use of this important and increasingly applied agricultural practice: the Cultivation of GR soybean. Thus, the aim of this work was to evaluate the effects caused by glyphosate applications on twenty GR soybean cultivars. Me rates applied were: check without herbicide; sequential application of glyphosate at 0.54/0.36 kg acid equivalent (AE) ha(-1), at 12/24 days after emergence (DAE); single application of glyphosate at 0.72 kg a.i. ha(-1), at 20 DAE: sequential application of glyphosateat 0.72/0.54 kg a.i. ha(-1), at 12/24 DAE: single application of glyphosate at 0.90 kg ha(-1). at 24 DAE. The variables root dry weight (RDM. shoot dry weight (SDW). accumulated nodule dry weight (ANDM and number of accumulated nodules (NAN) were evaluated. The cultivars MSOY 8008 RR, ANTA RR. CD 213 RR. MSOY 8100 RR, VALIOSA RR. CD 219 RR. MSOY 6001 RR, CRISTALINA RR and BRS 247 RR showed the highest susceptibility to the glyphosate applications, with reductions in at least three out of the four variables studied. BRS 242 RR. BRS 243 RR, BRS 244 PR, BRS 246 RR, CD 214 RR, MSOY 8151 RR, MSOY 9000 RR and BRS 245 RR showed the highest tolerance. with no significant reductions or only in one of the four assessed variables. In general. RDW was more affected by the mode of application than the glyphosate rate: however, SDW and nodulation (ANDW and NAN) were more affected in the longer cycle cultivars. compared to the earlier cycle varieties. Nodulation was also less affected by glyphosate in the BRS variety group, Compared to other genetic materials.