Abstract
Cotton (Gossypium hirsutum L.) cultivars transgenically enhanced to impart herbicide resistance to either bromoxynil [3,5‐dibromo‐4‐hydroxybenzonitrile; BXN (Bayer Advanced, Peoria, IL)] or glyphosate [N‐(phosphonomethyl)‐glycine; Roundup Ready (Monsanto Co., St. Louis, MO)], and/or Bacillus thuringiensis var. kurstaki [Bt; Bollgard (Monsanto)] mediated resistance to certain lepidopteran insects were planted to 77% of the 2002 U.S. cotton hectarage, yet Official Cultivar Trial (OCT) protocols remain little changed since inception. The presence of transgenic, pest‐managing, and nontransgenic cultivars in OCTs poses challenges to provide unbiased cultivar performance because OCTs impose herbicide and insect management regimes appropriate for nontransgenic cultivars. Our objectives were to assess the merits of OCTs to test transgenic and nontransgenic cultivars and to recommend alternatives. Because OCTs levy common pest management on all cultivars, value‐added transgenic traits are not demonstrated, cultivar variation in their expression is not shown, and main effects and interaction of cultivar and pest management regime are confounded. Examples of pest management main effects that potentially affect cultivar ranks in OCTs include yield penalties imposed on herbicide‐resistant cultivars from routinely used, soil‐applied herbicides and yield advantages imparted to Bt cultivars from added insect control of OCT insecticide regimes. One recommendation to more comprehensively test cultivars is to augment OCTs with trials wherein the best performing transgenic and nontransgenic cultivars in OCTs are produced with their respective pest management programs. Such trials simultaneously evaluate cultivars and transgenic traits for yield, fiber quality, and economic returns. Still, bias imposed by nontransgenic pest management regimes in OCTs can only be quantified through trials levying transgenic and OCT‐type pest management treatments on transgenic cultivars.
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