Challenges in Testing Transgenic and Nontransgenic Cotton Cultivars

tandem with transgenic technology, while also questioning the validity of OCT performance data. Cotton (Gossypium hirsutum L.) cultivars transgenically enhanced A key role of cultivar testing is to provide unbiased to impart herbicide resistance to either bromoxynil [3,5-dibromoagronomic performance in a defined environment while 4-hydroxybenzonitrile; BXN (Bayer Advanced, Peoria, IL)] or glyphoemploying an accepted, common management system. sate [N-(phosphonomethyl)-glycine; Roundup Ready (Monsanto Co., St. Louis, MO)], and/or Bacillus thuringiensis var. kurstaki [Bt; BollThe primary goals of cotton OCTs are to rank cultivars gard (Monsanto)] mediated resistance to certain lepidopteran insects within and across locations for lint yield, lint fraction were planted to 77% of the 2002 U.S. cotton hectarage, yet Official (ratio of lint to seed-cotton), and fiber properties. BeCultivar Trial (OCT) protocols remain little changed since inception. fore the advent of transgenic, pest-managing cultivars, The presence of transgenic, pest-managing, and nontransgenic cultiimposition of common insect and weed management vars in OCTs poses challenges to provide unbiased cultivar perforprotocols on all cultivars in OCTs was an accepted pracmance because OCTs impose herbicide and insect management retice. Differential effects of the common pest managegimes appropriate for nontransgenic cultivars. Our objectives were ment system on certain cultivars in OCTs may have to assess the merits of OCTs to test transgenic and nontransgenic existed, but such bias was not considered of sufficient cultivars and to recommend alternatives. Because OCTs levy common magnitude to invalidate OCT results. Cotton germplasm pest management on all cultivars, value-added transgenic traits are can possess host resistance traits such as gossypol glands, not demonstrated, cultivar variation in their expression is not shown, and main effects and interaction of cultivar and pest management providing some protection from certain lepidopteran regime are confounded. Examples of pest management main effects insects (Parrott et al., 1989; Calhoun et al., 1997; Jenkins that potentially affect cultivar ranks in OCTs include yield penalties et al., 1997) compared with nonor less-glanded cultiimposed on herbicide-resistant cultivars from routinely used, soilvars. The elevated lepidopteran insect control afforded applied herbicides and yield advantages imparted to Bt cultivars from by gossypol can be further enhanced under more freadded insect control of OCT insecticide regimes. One recommendaquent insecticide application regimes appropriate for tion to more comprehensively test cultivars is to augment OCTs with non-host-resistant germplasm; hence, densely glanded trials wherein the best performing transgenic and nontransgenic culticultivars can have a yield advantage in OCTs (Lukefahr vars in OCTs are produced with their respective pest management et al., 1966). Cotton cultivars can also vary in leaf triprograms. Such trials simultaneously evaluate cultivars and transgenic chome density (Lee, 1985) and leaf shape (Thomson et traits for yield, fiber quality, and economic returns. Still, bias imposed al., 1987), traits associated with pest insect oviposition by nontransgenic pest management regimes in OCTs can only be nonpreference (Lukefahr et al., 1971; 1975), and requantified through trials levying transgenic and OCT-type pest manduced larval populations (Robinson et al., 1980). Thus, agement treatments on transgenic cultivars. bias from common pest management protocols imposed by OCTs existed before inclusion of transgenic cultivars (Bourland et al., 2000). The high level of lepidopterous C cultivars transgenically enhanced to impart insect control conferred by the Bt technology (Jenkins weed and/or insect pest management features have et al., 1997), plus the capability of herbicide-resistant been widely adopted since commercial introduction in cultivars to be produced with fewer soil-applied herbithe mid-1990s. About 77% of the 2002 U.S. cotton hectcides and potentially less herbicide-induced yield loss arage was planted to transgenic cultivars containing genes (S.C. Culpepper, 2002, personal communication; May conferring glyphosate herbicide resistance, Bt-mediated and Murdock, 2002), has led cultivar development firms, lepidopteran insect resistance, or both (glyphosate transgenic technology providers, and some producers Bt), plus smaller hectarage planted to bromoxynil-resisto question the validity of testing transgenic cultivars in tant cultivars (USDA-AMS, 2002). Thus, transgenic culOCTs and fairly comparing them with nontransgenic tivars can now be considered to be conventional cultivars cultivars. Our objectives were to assess the merits of because they dominate plantings. Despite the domiOCTs to test transgenic and nontransgenic cultivars and nance of transgenic cultivars in U.S. production, OCTs to recommend alternatives. remain the primary vehicle for testing cultivars. Transgenic technology developers, growers, and some scienThe First Contingent of Transgenic tists have advocated that OCT test protocols evolve in Cotton Cultivars A brief synopsis of the development of transgenic O.L. May, Dep. of Crop & Soil Science, Univ. of Georgia, Coastal Plain cultivars affords a broader understanding of their appeal Exp. Stn., P.O. Box 748, Tifton, GA 31793-0748; F.M. Bourland, Univ. to growers. Plus, it is instructive to describe the pest of Arkansas, Northeast Res. and Ext. Ctr., Keiser, AR 72351; and R.L. Nichols, Cotton Incorporated, 6399 Weston Parkway, Cary, NC 27513. management features of transgenic cultivars to appreciReceived 5 July 2002. *Corresponding author ([email protected]). ate the complexities of conveying performance of the Published in Crop Sci. 43:1594–1601 (2003).  Crop Science Society of America Abbreviations: Bt, Bacillus thuringiensis var. kurstaki; OCTs, official cultivar trials. 677 S. Segoe Rd., Madison, WI 53711 USA