For many hundreds of years, breeders have been using a multitude of tools and tricks to modify tuber-producing species of the genus Solanum (of the nightshade family) into the great variety of potatoes that we now grow. Today’s tools go far beyond simple cross-pollination and selection of plants. Many of our current technologies are laboratory-based, and although the terminology may not be familiar and the science may seem technical, the end goal remains the same as that pursued by earlier breeders: to introduce new traits into an already successful crop, and to generate even healthier and more productive cultivars.
For years, potato breeding has relied on these kinds of laboratory technologies to reduce or increase the number of chromosome sets in a plant (diploid have 24 chromosomes; tetraploid have 48), to fuse nuclei from different potato species, and to make crosses between potatoes and their wild relatives. To these tools scientists have added laboratory approaches, such as marker-assisted selection, to greatly speed up breeding efforts.
A separate approach for adding valuable traits to many crops has been developed over the last three decades since its introduction in 1983. This approach to plant improvement is commonly referred to as genetic engineering or genetic modification (GM for short). The first documented use of this in potatoes appeared in 1986, and commercially available GM potato lines were introduced relatively shortly thereafter, in the late 1990s.
There are two primary techniques for plant genetic engineering. One technique involves the use of a bacterium called Agrobacterium tumefaciens, and the other uses particle bombardment (a.k.a. the gene gun). Both of these methods introduce DNA segments that become incorporated into plant chromosomes and from then on are inherited like any gene. The DNA segments used in these cases can come from any source: plants, animals or microbes. For example, resistance to glyphosate is generated by introduction of a bacterial gene that provides tolerance to the herbicide, and late blight resistance can be conveyed to potatoes by introducing resistance gene(s) from wild relatives of potato. The resulting plants are extensively tested to determine whether they express the desired trait and have no unforeseen effects on the crop.
Use of these technologies make it possible to introduce genes previously unavailable to conventional potato breeders and in some cases expedite the breeding process, since even when useful traits are found in wild relatives, it takes numerous generations to transfer them to potatoes using traditional practices.
A slightly different approach to genetic engineering is called gene silencing, which is a process where the introduced DNA results in lower levels (silencing) of a protein, such as an enzyme, and thus gives rise to a new trait. The introduced DNA is always from the same species and does not result in new proteins. One example of gene silencing is the introduction of potato DNA into established cultivars that lowers their levels of the enzyme polyphenol oxidase, generating a low bruise tuber. A similar process has been used successfully to silence the same enzyme in apples to generate non-browning fruit.
A new generation of technologies (such as TALENS and CRISPR-Cas9) is under development. These technologies will allow breeders to make targeted changes to DNA, such as changing a single base in a specific gene, without leaving any foreign DNA behind in the plants. This new generation of tools will allow us to choose whether to silence or increase the expression of one of the plant’s own genes, according to how we want that gene to behave. After the initial genetic engineering, conventional breeding can be used to move the proven trait into other cultivars that may be preferred by some farmers or consumers.
All plants produced by any of these GM technologies are extensively tested to determine whether they express the desired trait and have no unforeseen effects on the crop. The United States relies on a coordinated framework for regulating genetic engineering of plants involving three federal agencies: the USDA’s Animal and Plant Health Inspection Service (APHIS), the U.S. Environmental Protection Agency (EPA) and U.S. Food and Drug Administration (FDA). The scientific consensus is that the methods of genetic engineering are safe for the consumer and carry no greater risk to the environment than similar traits developed by more conventional means.