Thursday, November 1, 2012
Tall spindly lettuce plants in a Salinas greenhouse don’t look remotely appetizing – but they might be the future of salad.
Research Horticulturist Jim McCreight coordinates melon and lettuce breeding at the U.S. Department of Agriculture research station just south of Salinas, where plastic baggies are sometimes fastened to the tops of plants to capture pollen.
McCreight is like a modern-day Gregor Mendel, famous for the pea crossing experiments you studied in high school biology. It involves lots of trial and error. He and a team of breeders will cross a plant with a desired trait – like, say, resistance to downy mildew – with one that’s susceptible to the disease. If the resulting generation has the desired disease resistance, they might have a dominant trait. They’ll then let that plant self-pollinate, and start a new generation.
The breeding Salinas researchers do today is an extension of work that began in the mid-’20s in the Imperial Valley after breeders found a variety that was resistant to brown blight, which was wiping out the winter supply of lettuce.
“All we need is one plant,” McCreight says. “But sometimes finding that one plant takes a long time.” They’ve got lettuces gathered in the Balkans and Turkey, a range of light green to crimson to purplish, growing in short rows.
Some 85 percent of spinach seed carries the fungal pathogen verticillium wilt, which can linger in soil for up to 20 years. It infects otherwise healthy lettuce when it’s just days from harvest-ready, turning mature crops into fields of leafy mush within as little as 48 hours.
Breeders are hopeful that some wild varieties will prove resistant to verticillium wilt – but if they make the right cross, much of the work in breeding is yet to be done. Most wild lettuces are too bitter or prickly to be any good in a salad.
While diseases can move fast, traditional plant breeding is slow going. Each generation has half the genetics of the original parent; six generations into crossing, you’re left with just 3.125 percent of the original genetics. That means getting the desirable traits – like color, crispness, flavor – back into a disease-resistant strain is its own breeding project in reverse.
McCreight swirls seeds in a jar as he describes “back-crossing,” or pollinating the new plants with seeds from their parent stock. “After about seven generations of back-crossing, you’ve reconstituted about 99.9 percent of that back-parent with the traits you want,” he says. “It sounds easy, but it takes 10 or 12 years to develop something that resembles lettuce.”