Estrategias biotecnológicas para la obtención de cultivos tolerantes a herbicidas

Weeds are one of the main challenges the agricultural sector has to tackle, as they compete against crops for essential resources such as water, nutrients, and space, causing major losses in yields. Transgenic herbicide-tolerant crops were developed in the ‘90s, allowing growers to simpler, more effective, and more economical chemical control. This work has aimed to collect the technologies behind the development of transgenic and gene-edited herbicide-tolerant crops, as well as to review their environmental impact and the legal aspects around them in the European Union. These targets will be achieved by consulting peer-reviewed scientific data in bibliographic databases such as Scopus and Pubmed, as well as technical reports and specific platforms such as ISAAA, EUGINIUS, and EU-SAGE. Herbicide-tolerant crops are mainly developed by introducing a bacterial gene that confers herbicide tolerance into the crop’s genome. The introduced transgene will preferably metabolize the herbicide molecule into an inactive form. If this strategy does not fulfill good results, the inserted transgene would code for an insensitive form of the targeted enzyme from a resistant organism. Glyphosate-tolerant crops have been rapidly implemented in many countries, especially soybean, corn, canola, and cotton crops, which has led to great economic benefits for farmers. Nevertheless, transgenic crops are strictly regulated in many countries, and they have not achieved social acceptance in European countries. In the last few years, accurate gene editing technologies have enabled scientists to develop herbicide-tolerant crops without inserting transgenes. The most used gene editing technologies for the development of herbicide-tolerant crops are CRISPR/Cas9 and base editing, although prime editing is a novel mechanism that will probably be widely adopted in the following years. Some of the plants obtained by these methods are indistinguishable from the ones that have naturally evolved, so the scientific community, especially the European one, is demanding laxer legislation that would enable a quicker introduction of gene-edited crops into the market. Herbicide-tolerant crops began as a more sustainable option than conventional crops, as they promoted the substitution of highly toxic herbicides and the reduction in herbicide use. However, these crops have been used as the only control method in most of the lands where they were grown, which led to the spread of resistant weeds and the increase in herbicide use. Moreover, unsustainable agricultural practices such as monocultures and lack of crop rotation have been associated with herbicide-tolerant crops. After a few years of adoption, herbicide-tolerant crops started to cause a more negative environmental impact than conventional crops, in the countries where its production is widely adopted. Hence, European institutions have decided not to include herbicide-tolerant crops in the new proposal for regulation about crops developed by New Genomic Techniques, which will facilitate the approval for the production of these crops in the European territory.