Dec 20, 2018

Scientists fight for the pickle against downy mildew

With failed harvests, fewer growers are taking a chance on cucumbers. According to USDA records, pickling cucumber acreage declined nearly 25 percent between 2004 and 2015. Globally, downy mildew threatens fields as far flung as India, Israel, Mexico and China.

“This is the number one threat to the pickle industry,” says vegetable pathologist Lina Quesada-Ocampo of North Carolina State University. The growers, she says, lose money on failed crops and pricey fungicides. “It is a really bad double whammy.”

Fortunately for pickle lovers, vegetable breeder Michael Mazourek of Cornell University is close to releasing varieties that resist downy mildew. “It’s been one of our proudest David and Goliath stories,” he says. But his success hinges on funding at a time when public support of agricultural research is declining.

The story of saving the pickle, then, is not just about preserving the deli sandwich’s sidekick. It’s a story of how much we value our food supply. And who we think should pay to protect it.

According to a story by National Public Radio, cucurbit downy mildew, caused by the fungal pathogen Pseudoperonospora cubensis, was once a minor nuisance. Starting in the 1960s, a Clemson University plant breeder, Carroll Barnes, produced a series of cucumber cultivars containing a strong resistance gene known as dm-1. For more than four decades, this gene helped keep the disease in check.

But in 2004, the pathogen overwhelmed the defense. In North Carolina, pickling cucumber growers were a third of the way through harvesting when downy mildew arrived. Within about a week, the crop “almost melted,” says Thomas Joyner, president of Nash Produce. “It burned the leaves and there was almost nothing left.”

That year, downy mildew struck cucumbers from Florida to New Jersey. The following year, it reached Michigan, the number one pickling cucumber state. And it has spread from Florida every summer since.

According to the NPR story:

“Growers turned to fungicide, but downy mildew quickly adapts faster than the industry can release new ones. “Some that were very effective just a few years ago are absolutely ineffective now,” says Phil Denlinger, vice president of agricultural procurement for Mt. Olive Pickle Company. “It is a serious situation.”

Breeding in resistance

Every year we wonder, will our tools hold up?” says plant pathologist Mary Hausbeckof Michigan State University. As extension specialists for each of their states, Hausbeck and Quesada-Ocampo test fungicides and advise growers on methods that remain effective.

In 2014, Hausbeck was becoming increasingly concerned about running out of means for growers when she approached Cornell’s Mazourek with a personal plea for help. As she saw it, the industry was at terrible risk and, having grown up in Michigan pickle country, she hated to see it collapse. She recalls Mazourek listening politely and then saying, “You know, we might be able to do something.”

Mazourek had already developed a downy mildew resistant slicing cucumber, the kind we eat fresh on a salad, by crossing two cultivars with moderate levels of resistance and then selecting the most hardy offspring over multiple generations.”

To view the full NPR story, visit here.

Photo: Every summer, downy mildew spreads from Florida northward, adapting to nearly every defense pickle growers have in their arsenals and destroying their crops. Photo: Bernd Settnik/Picture Alliance via Getty Images