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Effect of Synthetic Auxin Herbicides on Seed Development and Viability in Genetically Engineered Glyphosate-Resistant Alfalfa

  • Sandya R. Kesoju (a1), Rick A. Boydston (a2) and Stephanie L. Greene (a3)


Feral populations of cultivated crops have the potential to function as bridges and reservoirs that contribute to the unwanted movement of novel genetically engineered (GE) traits. Recognizing that feral alfalfa has the potential to lower genetic purity in alfalfa seed production fields when it is growing in the vicinity of foraging pollinators in alfalfa seed fields, industry has established production standards to control feral plants. However, with the commercialization of GE glyphosate-resistant (GR) alfalfa and the need to support the coexistence of both GE and conventional production, effective methods to control transgenic feral alfalfa need to be developed. Therefore, a study was conducted in 2012, 2013, and 2014 to determine the effect of several synthetic auxin herbicides on seed development in GR alfalfa. GR alfalfa, var. Genuity (R44BD16), was treated with dicamba, 2,4-D, triclopyr, and aminopyralid when alfalfa plants contained green seed pods. Two weeks after herbicide application, plants were harvested, air dried, and seed yield, seed germination, and seedling emergence from the soil were determined. In 2013, dicamba, triclopyr, and 2,4-D decreased alfalfa seed yield per plant compared wih nontreated plants, whereas in 2014, all four herbicides decreased alfalfa seed yield per plant 24 to 49% (by weight) compared with nontreated plants. The same trend was evident in 2012, but seed yield was variable and was not significantly different among treatments. Seed germination averaged 43, 50, and 72% in 2012, 2013, and 2014, respectively, and was not affected by the four herbicides applied at early pod-fill stage. However, seeds harvested from plants treated with dicamba, 2,4-D, and triclopyr often produced deformed and abnormal seedlings, and when planted in soil, frequently failed to emerge. The combined effects of dicamba, 2,4-D, and triclopyr in reducing seed yield, seedling emergence, and seedling growth could contribute to managing feral alfalfa populations.

Poblaciones ferales de cultivos tienen el potencial de funcionar como puentes y reservorios que contribuyan al movimiento indeseable de nuevas características producto de la ingeniería genética (GE). Al reconocer que la alfalfa feral tiene el potencial de reducir la pureza genética en los campos de producción de semilla de alfalfa cuando crece en la vecindad de polinizadores de campos de semilla de alfalfa, la industria ha establecido estándares de producción y de control de plantas ferales. Sin embargo, con la comercialización de alfalfa GE resistente a glyphosate (GR) y la necesidad de apoyar la coexistencia de producción GE y convencional, se necesita desarrollar métodos efectivos de control de alfalfa feral transgénica. Por esta razón, se realizó un estudio en 2012, 2013, y 2014 para determinar el efecto de varios herbicidas del grupo auxinas sintéticas sobre el desarrollo de la semilla en alfalfa GR. Alfalfa GR, var. Genuity (R44BD16) fue tratada con dicamba, 2,4-D, triclopyr, y aminopyralid cuando las plantas de alfalfa tenían vainas verdes. Dos semanas después de la aplicación del herbicida, las plantas fueron cosechadas, secadas al aire, y se determinó el rendimiento de semilla, la germinación de la semilla, y la emergencia de plántulas del suelo. En 2013, dicamba, triclopyr, y 2,4-D disminuyeron el rendimiento de semilla de alfalfa por planta en comparación con plantas sin tratamiento, mientras que en 2014, todos los cuatro herbicidas disminuyeron el rendimiento de la semilla de alfalfa por planta 24 a 49% (por peso) al compararse con plantas sin tratamiento. La misma tendencia fue evidente en 2012, pero el rendimiento de semilla fue variable y no fue significativamente diferente entre los tratamientos. La germinación de la semilla promedió 43, 50, y 72% en 2012, 2013, y 2014, respectivamente, y no fue afectada por ninguno de los cuatro herbicidas aplicados temprano durante el estadio de llenado de la vaina. Sin embargo, las semillas cosechadas a partir de plantas tratadas con dicamba, 2,4-D, y triclopyr frecuentemente produjeron plántulas deformadas y anormales, y cuando estas fueron sembradas en el suelo, frecuentemente fallaron en emerger. Los efectos combinados de dicamba, 2,4-D, y triclopyr sobre la reducción del rendimiento de la semilla, la emergencia de las plántulas, y el crecimiento de plántulas podría contribuir a manejar poblaciones ferales de alfalfa.


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Associate Editor for this paper: Prashant Jha, Montana State University.



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