Go to the grocery on any afternoon to buy a cucumber, and you’ll probably find what you expected: a cucumber that looks pretty much like every other you’ve ever bought. When you take it home and chop it up in your salad, perhaps it tastes a bit fresher, or it’s slightly firmer than the last cucumber you had. Overall, you reason, it’s a cucumber and that’s that. Or is it? “The world is not static,” says Michael R. Mazourek, School of Integrative Plant Science, Plant Breeding and Genetics. “It’s easy to think that produce is as it always was, but there’s a lot going on behind the scenes. Even if your cucumber doesn’t look different than it did last year, probably it actually is different.”
Mazourek is a vegetable breeder, one of the researchers behind the scenes who is constantly working with our produce to make it better. He focuses especially on peppers, peas, and cucurbits—the family that includes cucumbers, squash, melons, and watermelons. Every year he puts out around 10,000 plants in his research plots then observes their growth through the season, assessing them for yield, quality, and disease resistance. “More and more, we also look into the genomes of these crops,” he says. “For most of the plants in my field, we have some genomic information, which can range from knowing the form of a gene a plant carries for a couple of key characteristics to plotting several thousand data points across a plant’s genome.”
The Organic Model for Sustainability
Both observational and genomic information help Mazourek select the plants that he will cross-pollinate to produce offspring with desired characteristics that are especially attractive to organic growers. “Many exciting new solutions are coming from the organic community,” he says. “Organic done right is a model for a lot of what we want to do for sustainability. A key part is understanding the ecology of the plant and its environment, so you do less to disrupt it.” Organic growers need a plant that is resilient on its own merit. Unlike conventional agriculture where growers can use synthetic chemicals to enhance plant performance, in an organic system the plant has to be more disease and insect resistant, as well as able to thrive on non-petrochemical fertilizers.
Cucumbers and Downy Mildew
Breeding pest and disease tolerance into a plant can take a long time. For some years, Mazourek has been addressing the threat caused by downy mildew, a fungus-like pathogen that attacks plants in the cucurbits family. “Downy mildew was under control for years,” Mazourek explains. “And then it evolved and reemerged about a decade ago and started wiping out cucumbers, which are especially susceptible.”
“We can use the full gamut of all the technology at Cornell to ask questions about why the plant behaves the way it does and how the insect perceives it.”
To create a cucumber that could resist this new form of the pathogen, Mazourek and his team began with a breeding line from decades ago that was preserved in Cornell’s seed vault, which includes seeds from as far back as the 1940s. The researchers made a cross between two cucumbers with moderate resistance to downy mildew. Then they planted a few thousand progeny from that cross out in the fields and came back after the pathogen had swept through the area to see which plants were still standing. “There were a couple still alive,” Mazourek says. “We brought cuttings back to the greenhouse and cross-pollinated them, then planted the new population in the fields the next year and did it all over again. It’s really a sort of facilitated evolution.”
Every two years, Mazourek would release incremental improvements for sale as seed to organic growers. Conventional growers, meanwhile, had a set of fungicides they relied on to keep the mildew in check. “Then the pathogen developed resistance to the chemical controls,” Mazourek says, “and the fungicides started to fail. At that point, the only thing left was genetic resistance. When the disease is around, our plants are the only option. Now everyone is interested in them.”
Recently Mazourek and his fellow researchers released a paper detailing the breeding of the first cucumber to have true resistance to downy mildew. The new cultivar illustrates the strengths of breeding for a sustainable system like organic farming, he says. “You plant your fields with plants that are going to be fine pretty much on their own, instead of dealing with the cost, labor, and environmental concerns of pesticides. Breeding for resilience takes more time, but we are the long-term solution to the problem.”
Which Squash Do the Beetles Like?
In another breeding project, Mazourek is looking into the reasons for the taste preferences of striped cucumber beetles. The beetles love zucchini but ignore summer squash. Yet zucchini and summer squash are subspecies of the same original wild squash. “They were domesticated independently in the southern U.S.,” Mazourek explains, “and in the process humans captured different characteristics in the plants that were domesticated. Now we’re crossing the two subspecies and looking to see which ones the beetles like and which they don’t, and asking, ‘what is the genetic difference?’”
Using mass spectrometry, Mazourek looks at the plants’ volatile cues, the differences in the chemical composition of the leaves. He also looks at gene expression—which genes are active and which are not—in an effort to pinpoint what might be attracting or deterring the beetles. “I really enjoy that we have an observation we can’t explain yet,” he says. “That’s one of the strengths of plant breeding, that even before we understand how something works we can deliver the tools and advances by creating new cultivars that fulfill the need. Then, I get to take off my field boots and come into the lab. We can use the full gamut of all the technology at Cornell to ask questions about why the plant behaves the way it does and how the insect perceives it.”
Mazourek grew up on a dairy farm in Newfield, New York, just down the road from Cornell University. “I have that connection to agriculture and the importance of farms in New York,” he says. “When Cornell reinvested in getting the region’s farmers the seeds they needed, it was really special that I got to come here to do that work.”