Aryloxyalkanoate dioxygenase-12 transformed soybean biological response, protein expression, and off-site movement of 2,4-d and dicamba

Andrew P Robinson, Purdue University

Abstract

The over-reliance and continued use of glyphosate as the sole mechanism for weed control has led to the selection of glyphosate-resistant weeds. New trait technology incorporating 2,4-D tolerance in soybean will provide an alternative method to control weeds that are hard to control with glyphosate alone and reduce selection pressure by tank mixing herbicides with 2,4-D, but the response of aryloxyalkanoate dioxygenase-12 (AAD-12) transformed soybean have not been evaluated. In addition, off-site movement of auxinic herbicides on sensitive soybean will be of greater concern as 2,4-D and dicamba will be applied at a field-scale level during the peak growing season with new transgenic crops becoming commercially available in the near future. The purpose of my research was to quantify the effects of 2,4-D timing and rates on AAD-12 soybean yield components and AAD-12 protein expression; characterize the effects of dicamba and 2,4-D rates on sensitive soybean plants; and analyze the effect of 2,4-D plus glyphosate on summer annual weeds. It is conclude that 1) AAD-12 soybean plants can tolerate up to 2,240 g ha-1 2,4-D. Seed yield, seed mass, pod number, seed number, seed per pod, reproductive node number, pods per reproductive node, node number, and percent reproductive nodes were not affected by 2,4-D when applied at the V5, R2, or the V5 followed by the R2 soybean growth stages of AAD-12 soybean plants. 2) The youngest fully emerged trifoliate in the DAS-68416-4 event had the highest AAD-12 expression, with means ranging from 369 to 390 ng cm-2, while the older leaves maintained a lower level of expression, 171 to 211 ng cm-2. The youngest leaves of event DAS-21606-3 had the highest level of AAD-12 protein expression (205 to 225 ng cm-2), while the level of AAD-12 was lower in older leaves (71 to 149 ng cm-2). In general, 2,4-D treatments did not reduce AAD-12 protein expression at 3, 7, 14, and 21 days after treatment; however, in a few instances AAD-12 protein expression was increased or decreased by 8 to 11% after 2,4-D treatment. 3) Glyphosate at rates ≥ 840 g ha-1 controlled giant ragweed, common lambsquarters, common waterhemp, and velvetleaf by 94 to 100%. Giant ragweed was controlled 99 to 100% by 2,4-D alone when rates were ≥ 280 g ha-1. Common lambsquarters, common waterhemp, and velvetleaf control increased as 2,4-D rates increased, with 1,120 g ha-1 providing 90 to 94% control. 4) Sensitive soybean seed yield was reduced by 5% when 87 to 116 g ha-1 2,4-D was applied and a 10% reduction was caused by 149 to 202 g ha-1 2,4-D. 5) Dicamba treatments applied to sensitive soybean reduced seed yield by 5% from 0.042 to 0.528 g ha-1 and a 10% reduction was caused by 0.169 to 1.1 g ha-1 dicamba. Path analysis indicated that seeds m-2, pods m-2, main stem reproductive nodes m-2, and main stem nodes m -2 were the most influential yield components in seed yield formation when either 2,4-D or dicamba treatments were applied to sensitive soybean plants. The introduction of 2,4-D-tolerant crops will allow add an addition method to control weeds that are resistant to glyphosate while not altering reproduction, but precautions need to be taken to avoid injury to nearby sensitive plants.

Degree

Ph.D.

Advisors

Johnson, Purdue University.

Subject Area

Agronomy|Agriculture|Plant sciences

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