Herbicide-resistant crops are a leading cause of undesirable farming practices
The introduction of transgenic plants, 30 years ago, was accompanied by hopes of reducing the use of pesticides in crop cultivation. It was argued that this would be particularly beneficial to the environment, health and to farmers. The theory: genetic engineering could be used to make plants resistant to herbicides. The herbicide-resistant transgenic crops could then be sprayed with broad-spectrum herbicides, such as glyphosate, during the growing season. It was reasoned that the herbicides would only be used when needed, thus promoting a more environmentally-friendly agriculture.
Initially, there was in some cases an actual reduction in herbicide use. However, the continuous and widespread cultivation of herbicide-resistant transgenic crops, which in some countries, e. g. the USA, accounts for over 90 percent of the cultivated areas, was soon followed by a significant increase in herbicide use. In maize, soybean and cotton fields, especially in the main cultivation areas of North and South America, the use of glyphosate, glufosinate, 2,4-D or dicamba in particular has risen substantially. One major cause is the spread of herbicide-resistant weeds, especially to glyphosate, as regular use of the herbicides puts considerable pressure on wild plants to adapt.
Early predictions warning of the emergence of herbicide-resistant weeds soon became a reality. The 'WeedScience' database currently includes about 60 weed species globally that are glyphosate-resistant. Most have emerged through the cultivation of genetically engineered crops. These weeds can either no longer be controlled with glyphosate, or only with very high dosages. In the US, glyphosate-resistant weeds can meanwhile be found growing on about 60 to 80 percent of the land planted with corn, soybeans or cotton.
New transgenic plants were developed to solve these problems, and they now have multiple resistances to different herbicides (so-called 'stacked events'). This has facilitated the use of additional herbicides during cultivation, which has again resulted in an overall increase in the use of pesticides. It has, in addition, furthered the development of multi-resistant weeds, some of which are now resistant to up to seven different active ingredients. The resulting economic and ecological damage is considerable.
In addition to the increasing pressure on weeds to adapt, genetic engineering is also affecting other factors that may have an impact on the amount of pesticide used. These include larger acreages, lack of crop rotation, decreasing diversification of cultivated crops and increasing dependence on large agrochemical corporations.
The positive effects on sustainability initially predicted have not materialized. On the contrary, in many regions, the cultivation of herbicide-resistant transgenic crops has contributed to the increasing environmental load with certain toxins, and thus to the destabilization of the affected agro-ecosystems. Furthermore, there is a risk that food and feed produced with the genetically engineered plants will typcially be loaded with a cocktail of these herbicide residues.
Experience gained from plants developed with 'old' genetic engineering must now lead critical scrutiny and forward-looking assessments of promises and expectations in regard to new genetic engineering. In many cases, the biotech industry is again advertising claims that ignore long-term consequences and are, instead, primarily focused on expected profits. Genetically engineered plants cannot be used as a substitute for an agricultural policy based e.g. on the findings of agroecology that promotes diversity in the fields. On the contrary, there is a high risk that incorporation of plants from new genetic engineering in industrial farming systems will perpetuate and even further expand undesirable farming methods.
‘Extreme’ traits can increase susceptibility to environmental stress
When breeding new plant varieties using conventional methods, there are some limitations which are due to certain protective mechanisms in the genome to preserve species-specific characteristics. As a result, conventional breeding methods (including random mutagenesis) cannot be used to achieve certain genetic changes, or only with great difficulty. However, new genetic engineering techniques (NGTs) can overcome these limitations and be used to develop completely new traits in plants. Genetic modification with NGTs is also much faster and more precise, thus significantly shortening the time it takes to develop new varieties. It is widely anticipated that the greater efficiency, speed and precision of NGTs in plant breeding will result in fewer side effects.
NGT modifications frequently result in ‘extreme’ or species-atypical breeding traits, which are often accompanied by undesirable side effects ('trade-offs'). This is reflected in the very small number of NGT plants currently available on the market. One example: Calyxt developed NGT soybeans with altered oleic acid composition in 2019. The soybeans were subsequently brought to market where they failed due to low crop yields. Calyxt has meanwhile re-aligned its business operations.
In a further example, NGT wheat was modified by knocking out several gene copies responsible for susceptibility to mildew. New genetic engineering techniques are more efficient in this respect than conventional methods and can achieve a more ‘extreme’ expression of the desired trait. However, this can also result in undesirable effects: apart from the observed mildew resistance, unintended effects were also observed, e. g. leaf chlorosis (bleaching), which did not occur with conventional breeding methods.
In another case, NGTs were used in wheat to knock out several copies of a gene crucial for the formation of asparagine, which is an amino acid that is ultimately responsible for the formation of carcinogenic acrylamide during baking. However, asparagine is also important for germination, plant growth, stress tolerance and defence against plant diseases. In this instance, it was found that the seeds of some varieties of this NGT wheat had very poor germinability. Furthermore, initial results from field trials showed changes in weight and number of grains.
The above examples show that new genetic engineering techniques can be used to produce ‘extreme’ traits that go beyond what can be achieved with conventional breeding. However, unintended side effects and interactions can occur even if the modification of the DNA sequence is targeted and precise. As such, these often ‘inevitable’ side effects can significantly slow progress in breeding. The ‘re-balancing’ of NGT plants may possibly require much more time to be spent on developing a trait compared to conventional breeding, thus making many breeding goals unattainable. n toxins, and thus to the destabilization of the affected agro-ecosystems. Furthermore, there is a risk that food and feed produced with the genetically engineered plants will typcially be loaded with a cocktail of these herbicide residues.
While NGTs offer great potential for genetic modification, it is not easy to translate this potential into actual benefits. Consequently, it is not possible to predict the time required between genetic modification and actual commercialisation of the final product.