Plant breeding: conventional v mutation v genetic modification (GMOs) v gene editing

Plant breeding is an art of improving crops to meet our needs. We all want and need food that looks good, tastes good and grows well. Decreasing rural populations but increasing urban and global population means food demands are at an all-time high. We’re constantly facing challenges to grow improved crops. Pests and disease are always evolving, and there’s climate change. These adversities threaten our food security and agricultural biodiversity. And to overcome these challenges, we must continuously breed new crop varieties that grow in different conditions and resist devastating diseases. Here, I give a brief overview of some of the most common practice of generating better crop varieties. These methods are vital to meet current and future food challenges including those set by climate, pests and diseases.

Conventional breeding

Farmers have crossed plants to introduce new traits for thousands of years. For example, let’s say we want the rice plant to be both pest resistance and produce a higher yield. But we have two rice varieties to start with: a) pest resistant but low yielding and b) high yielding but susceptible to the pest. We can cross these two rice varieties until we get a plant that’s both resistant to pests and produces a high yield. But then the offspring from these plants won’t always contain the two desired traits. The process still doesn’t end when we finally identify a plant that’s both pest resistant and high yielding. After we find the plant, there are a few rounds of selection and crossing until we get a genetically stable variant.

This process has been highly successful in the past and has delivered a great variety of plants that we have today. The process that I’m describing here is “hybrid breeding”, but “inbreeding” or “backcrossing” are also common breeding techniques. Conventional breeding is still an essential technique to generate new crop varieties and therefore for our food security. But it’s a tedious and painstakingly long process, and in comparison to other technology available to us, conventional breeding feels a bit out-of-date. Contrary to popular belief, traditional plant breeding is also a form of genetic modification that positively selects for traits. And it’s the genetic modification, which introduces these desired traits in a plant.

Chemical or radiation mutation breeding

Mutation breeding is another common breeding technology that’s much faster than conventional breeding. In this process, breeders use different methods to damage the DNA in seeds, and as a result, introduce mutations in plants. Radiations such as ultraviolet or gamma rays and chemicals such as mustard gas and EMS are typically used to induce artificial mutations at random. And if these random mutations generate a better trait in plants, we can select them to create an improved crop variety. We can also use biological technology and genetics to identify any unwanted mutations and positively select against the desired trait. Backcrossing against the first trait to positively select the mutated trait is often necessary to get rid of unwanted genetic modifications.

Mutation breeding is a highly successful and effective breeding technology that has significantly boosted genetic varieties. More than 3,280 mutant crop varieties across the world are available commercially.

Genetic modification (GM) breeding

Mainstream media and activist groups have portrayed GM technology as negative. As it happens, all GM crops commercially available are highly tested and safe to eat. There are some legitimate concerns such as intellectual ownership of the GM seeds and large-scale monoculture farms reducing agricultural biodiversity. But these seem to be policy and regulation issues. With stringent policy, I believe that genetic engineering can help the environment and boost biodiversity. As with any technology, there has to be a safety measure and assurance that it must pass before it’s safe for public use. And Genetically Modified Organisms (GMOs) aren’t any different. GMOs can be plants, animals, fish, etc. but I’m only focussing on plants here. See the Genetic Literacy Project to learn more about GM and genetic engineering in general.

GM is a molecular technology and a form of the genetic engineering process. It involves inserting DNA, responsible for a desirable trait, directly into the plant’s genome. Sticking to the analogy that I used earlier, it would be possible to make a rice variety that is both pest resistant and high yielding using GM technology. Although, a disadvantage is that the desired gene insertion into the plant’s genome happens randomly. This means there are some selection and screening required to ensure that the new gene isn’t affecting other genes already present in the plant. The screening process is rigorous, so if it’s not quite right, it won’t make the cut. Any selected GMO is trialled extensively to ensure that it’s safe to eat. But it does mean that the process is expensive.

There are different ways of delivering the desired gene into the plant, but a common approach is to insert the desired gene into bacteria called Agrobacterium and transfer them into the plant cell. The bacteria will then transfer the desired gene into the host plant’s genome. These plants produce seeds that contain the new gene that’s responsible for the desired traits. Critics of the GM technology often cite to the fact that GMOs contain foreign DNA, i.e. DNA transferred from bacteria into the plant’s genome. However, gene transfer from bacteria to a plant is a natural process that occurred over eight thousand years ago. That’s right – Mother Nature first made GMOs and, we have been eating them for thousands of years.

Gene editing (GE) breeding

GE is a new biological technology that allows precise modification of the genome. I like to think of GE as a part of the genetic engineering technology, but people often only include GM as genetic engineering technology. CRISPR–Cas9 (CRISPR) is the most common tool in genome editing. GE technology works when “molecular scissors” cut a location in the genome with precision. Scientists can then insert (new genes), remove genes or edit the part of the genome to introduce a desirable trait. The “genetic guides” or guide RNA show the molecular scissor or Cas9 the location to cut.

GE has several advantages over GM technology. While new gene insertion is random with GM, GE technology allows precise insertion of the desired gene. Additionally, there is no foreign DNA in the GE plant’s genome. As a result, plants that have been modified with GE technology are indistinguishable from the plants that are altered through conventional breeding or “naturally occurring” plants. Because of this, some even argue that GE plants aren’t even GMOs. Despite all this, the European Court of Justice ruled that any organisms that have undergone the GE technology are GMOs. In contrast, Japanese authorities ruled that only GM food that had “foreign DNA” require regulation, but the same restrictions don’t apply to GE food made through editing the genome.

In our battle to secure our food future, we need to explore and utilise new technologies. But the examples above demonstrate that technology and policy go hand-in-hand. In the case of genetic engineering, administrators certainly have a lot of catching up to do with the technology. Productive GM food certainly has the potential to be a big part of our food system. But it must be tied-up with stringent policy and regulations first.

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