Transgenic cottons for sustainable pest management

Transgenic cotton has significantly altered pest control in this crop during the last decade. Cotton was one of the first widely cultivated Bacillus thuringiensis (Bt) insect-resistant and herbicide-tolerant (Ht) transgenic plants. Over 300 transgenic cotton varieties expressing single or dual Bt proteins targeting lepidopteron larvae, as well as pyramided varieties with herbicide tolerance, are available to growers. Potential negative impacts of transgenic plants, however, have generated concerns over deploying these plants over extensive crop areas, such as those occupied by cotton. Nearly 8% of 33.8 million hectares has been cultivated with Bt cotton with the trend to increase in future seasons. Hence, weediness, gene flow, and impact on nontarget organisms by Bt and Ht cotton have been closely studied during the past decade. Despite justifiable concerns over potential risks, the data show neither a significant negative impact nor the development of field resistance by cotton pests. Results of nontarget impact registered four negative impacts on natural enemies, which are discussed here. No weediness and gene flow have been shown in over 333 published results, although little data exist for the risks of gene flow. Regarding insect resistance, several factors underline resistance appearance in field population, including species biology and interactions with the environmental conditions population. Modeling of the evolution of resistance in a field population to Bt proteins has been conducted and the use of single or dual Bt protein varieties might reach some failure due to resistance depending on gene frequency-conferring resistance in the population. Planting transgenic cotton, therefore, requires effort and vigilance to ensure sustainability of the system, including the planting of mandatory refuges and monitoring insect and weed resistance. This article presents and discusses seven sections beyond an introductory section: What is a transgenic plant, conventional and transgenic plant breeding methods in insect-resistant cotton, how transgenic cottons were developed (Bollgard®, WideStrike®, VipCot® and herbicide tolerant cottons), potential nontarget effects of Bt cottons, resistance and resistance management, Bt cotton perspective in Brazil, and the future of transgenic and pest management in cotton.