A new development in plant breeding may lead to some very fruitful results. This month, a team of scientists announced that they had identified and combined key genetic mutations to significantly increase fruit production in tomato plants. These results may be a first step towards increasing yield in other crops as well.
To create their productive new plants, researchers used a technique called mutation breeding. They exposed tomato seeds to DNA-altering chemicals to induce random changes in the plant’s genetic code; the team then searched for new, desirable traits in the resulting plants. The new plants are genetically modified, but different from what people typically call genetically modified organisms in that they contain no artificially introduced foreign DNA, writes Zachary Lippman, a researcher at Cold Springs Harbor Laboratory and an author of thenew study published in Nature Genetics.
Mutation breeding has been carried out for decades, says Robert Paarlberg, a political science professor at Wellesley College who researches food and agricultural policy. “We have in our food supply right now varieties of wheat and peanuts and grapefruit that have been developed using induced mutation and then breeding,” he says. The technique can also be used to develop ornamental crops and flowers, Paarlberg says, but says it’s not a “very precise” strategy. Plant breeders call the process “spray and pray,” Lippman says. Once the plants are treated, “you pray that you find something that’s useful,” he says.
Lippman and his team were praying for more flowers, which lead to more fruit. Plants like tomatoes naturally balance flowering activity with increasing leaf and plant size. Changing the behavior of only a few genes can profoundly alter how many flowers a plant produces or how bushy it becomes. Modern processing tomatoes, for example, have a mutated flower-repression gene; this results in bushy plants with bursts of flowers that produce easily harvestable fruit. Lippman and his colleagues sought new ways to modulate this system of flower production and repression.
The team discovered several new mutations that improved productivity. But to maximize fruit yield, Lippman and his colleagues mixed and matched their new mutations. Like humans and many other organisms, tomatoes have two alleles, or forms, of every gene. The researchers discovered that changing only one allele in certain flower-production gene pairs was enough to change the plant’s growth. Lippman thinks this could be particularly useful in agriculture, where “hybrid” or cross-bred plant varieties with mixed allele pairs are common. Lippman and his colleagues paired different mutations to produce several new plants with high fruit yield. In some cases, these new hybrid plants produced twice as much fruit as currently bred processing tomatoes.
The work shows promise in terms of both breeding applications and understanding regulation of plant architecture, says David Francis, a professor of horticulture and crop science at Ohio State University. But Francis has some doubts about the utility of mutation breeding. He notes that the process largely leads to lost functionality. Plant breeding also depends upon environmental conditions, he says. “I don’t believe that you can just build a perfect tomato in the lab and get it done in the field.”
There are other potential concerns associated with mutation breeding; for example, the National Research Council noted in a 2004 report that the process is not regulated for food or environmental safety. Still, Paarlberg sees little cause for concern. “They’ve been doing mutation breeding now for eighty years, and I’m not aware of anybody who’s been harmed by any of the crops that have been put on the market as a result,” he says.
Francis also questions the immediate utility of the new tomato plants: they are less compact than standard processing tomatoes, he says, which might make them difficult to harvest industrially. “This kind of work is only really a breakthrough if it goes hand in hand with changes in agronomic practices,” he says. “That said, the science is pretty cool.”
Lippman says that the tomato is simply a model. Similar modifications can be extended into other crops, with the likely next candidate being soybeans. “The most exciting thing to all of this is that you can fine-tune crop productivity,” Lippman says. Current GMOs mainly try to limit crop losses, he says, instead of producing more food. “But in the future, we’re going to have to look beyond that,” he says. “It’s not just about this particular way boosting yield in tomato,” he says. It’s also about “the issue of needing to produce more food in the future.”