Glyphosate-resistant junglerice (Echinochloa colona) from Mississippi and Tennessee: Magnitude and resistance mechanisms

Authors: Nandula, Vijay; MONTGOMERY, GARRET - University Of Knoxville; VENNAPUSA, AMARNATHA - Kansas State University; JUGULAM, MITHILA - Kansas State University; GIACOMINI, DARCI - University Of Illinois; Ray, Jeffery - Jeff; BOND, JASON - Delta Research & Extension Center; STECKEL, LAWRENCE - University Of Tennessee; TRANEL, PATRICK - University Of Illinois

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2018
Publication Date: 7/2/2018
Citation: Nandula, V.K., Montgomery, G.B., Vennapusa, A.R., Jugulam, M., Giacomini, D.A., Ray, J.D., Bond, J.A., Steckel, L.E., Tranel, P.J. 2018. Glyphosate-resistant junglerice (Echinochloa colona) from Mississippi and Tennessee: Magnitude and resistance mechanisms. Weed Science. 66:603-610.

Interpretive Summary: Recently, several incidents of glyphosate failure on junglerice have been reported in the midsouthern U.S., specifically in Mississippi and Tennessee. Scientists from the Crop Production Systems Research Unit and Crop Genetics Research Unit of USDA-ARS, University of Tennessee, Kansas State University, Mississippi State University, and University of Illinois conducted research to confirm resistance to glyphosate, measure the magnitude of resistance, and to determine the mechanism(s) of resistance to glyphosate in junglerice populations from Mississippi (MSGR4) and Tennessee (TNGR). The resistance indices of MSGR4 biotype and TNGR population indicated they were 4- and 7-fold, respectively, resistant to glyphosate relative to the susceptible MSGS population. The absorption patterns of 14C-glyphosate in the TNGR and MSGS populations were similar. However, the MSGS population translocated 13% more 14C-glyphosate out of the treated leaf compared to the TNGR population. EPSPS gene sequence analyses of TNGR junglerice indicated no evidence of any point mutations, but several resistant biotypes including MSGR4 possessed a single nucleotide substitution of T for C at codon 106 position resulting in a proline to serine substitution. Results from qPCR analyses suggested that there was no amplification of the EPSPS gene in the resistant populations and biotypes. Thus, the mechanism of resistance in the MSGR population is, in part, due to a target site mutation at the 106 loci of EPSPS gene, while reduced translocation of glyphosate was found to confer glyphosate resistance in the TNGR population. The above results indicate the necessity of developing junglerice management strategies that include chemical, cultural, and mechanical tools.

Technical Abstract: Recently, several incidents of glyphosate failure on junglerice have been reported in the midsouthern U.S., specifically in Mississippi and Tennessee. Research was conducted to confirm resistance to glyphosate, measure the magnitude of resistance, and to determine the mechanism(s) of resistance to glyphosate in junglerice populations from Mississippi and Tennessee. ED50 (dose required to reduce plant growth by 50%) values for a resistant MSGR4 biotype, a resistant TNGR population, and a known susceptible MSGS population were 0.8, 1.62, and 0.23 kg ae ha-1 of glyphosate, respectively. The resistance index calculated from the above ED50 values indicated that the MSGR4 biotype and TNGR population were 4- and 7-fold, respectively, resistant to glyphosate relative to the MSGS population. The absorption patterns of 14C-glyphosate in the TNGR and MSGS populations were similar. However, the MSGS population translocated 13% more 14C-glyphosate out of the treated leaf compared to the TNGR population at 48 h after treatment. EPSPS gene sequence analyses of TNGR junglerice indicated no evidence of any point mutations, but several resistant biotypes including MSGR4 possessed a single nucleotide substitution of T for C at codon 106 position resulting in a proline to serine substitution (CCA to TCA). Results from qPCR analyses suggested that there was no amplification of the EPSPS gene in the resistant populations and biotypes. Thus, the mechanism of resistance in the MSGR population (and associated biotypes) is, in part, due to a target site mutation at the 106 loci of EPSPS gene, while reduced translocation of glyphosate was found to confer glyphosate resistance in the TNGR population.