by Sally Colby
There’s no question that potatoes are a staple in almost every American’s diet. Potatoes usually appear on grocers’ shelves in nondescript bags, but there’s a lot of science behind every variety that makes it to the shelf.
Dr. David Douches, director of the Michigan State University Potato Breeding and Genetics Program, says that the university’s program aims to bring new specialty potatoes to small growers.
“We’ve been running the potato breeding program at Michigan State University for about 28 years,” said Douches. “Our philosophy is to link the lab to applied solutions. We go from the lab to the breeding house to the field to get new varieties out there.”
Douches said a major component of the program is variety development and commercial release. “All the science behind that is to get new varieties out for farmers, and ultimately, consumers will benefit. We also want the varieties we bring out to have disease resistance and other enhancements.”
The arduous process begins in January when crosses are made in the greenhouse. “When we make a controlled cross, we end up with a ball of fruit,” said Douches. “Each of those fruit has seeds, and every one of those seeds is genetically different from each other. We make hundreds of crosses, and each year we produce about 65,000 new progeny to evaluate.”
Douches said it takes about 10 years from the initial cross to having a handful of selections that will be trialed. “The first four years of the program are the most critical because that’s when we’re trying to identify the best lines,” he said. “Then we take those best lines and whittle them down to a smaller group.”
A strategic grant initiative provided funding for Douches to explore trends in breeding and marketing specialty potatoes. “There are a lot of interesting varieties out there, and there’s a trend for specialty potatoes,” he said. “How do we get them out into the industry? We do a lot of breeding for chip processing potatoes in Michigan, and we have a nice system where we have a partnership between the breeding program, the commercial and seed growers and the processors that would pull new varieties through the evaluation process and get them to the market.”
But for the table market, the system isn’t as unified. Douches and his team determined that they needed to get into certified seed production. “I was able to get funds to establish a certified seed lab and greenhouse with the idea that we can bring specialty varieties to market,” he said. “We can also do this with some of the new chip varieties.”
Each year, trials at the research farm yield new and interesting varieties, and some participating growers also trial new table varieties. “Chip breeding is the driver, but we also try to supply the table market,” said Douches. “Not russets, but the round red, white, yellow and pigmented varieties.” Douches added that when new varieties are trialed, he’s looking beyond suitability for chipping or table use — he’s interested in disease resistance (scab and late blight) and keeps close tabs on those traits.
For the table market, economics on a farm scale and market appeal are among the two most important factors. Douches noted that all potatoes released have fared well in cooking and taste tests and described several of the most promising new specialty varieties: the “Michigan Purple,” which has purple skin and bright white flesh and has proven to be a good eating potato. However, the skin is somewhat thin and tends to skin easily. During trialing, several sports of the Michigan Purple were discovered. “It’s red with splashes of purple,” said Douches. “We put it in tissue culture and it maintained the unique appearance. A few years later, we found a white sport. These don’t seem to skin as much as the purple, but still have the same cooking qualities as the original variety.”
Douches described the variety “Purple Haze” as having splashes of purple around the eyes and apical end of the tubers with a creamy white flesh. The “Spartan Splash” is similar, with splashes of purple on yellow skin and creamy yellow flesh.
“Colonial Purple is a progeny of Michigan Purple, and we got some scab resistance in it,” said Douches, adding that scab resistance is an important trait for nearly all potato growing regions. “It kept the white flesh and the people who are using this variety are using it as a mini-blue. They aren’t growing them to full size — just using them as small potatoes in farmers markets. Instead of trying to pack it in with tight spacing, these varieties are naturally smaller in size. This management concept of getting small potatoes might be a little easier with a potato that has matches the market that you’re shooting for.” But it’s always a challenge to combine the most desirable traits including smaller size, higher number of tubers, scab resistance, flavor and consumer acceptance in one potato.
In 2013, the program initiated the use of cryotherapy for virus eradication. Douches compares cryotherapy to meristem culture without the heavy-duty microscope work. “If a plant has a virus, we get it into tissue culture,” he said. “Then we freeze the tips of the tissue culture plants in liquid nitrogen, then plate them out. The growing point starts coming back, and what’s left in most cases is virus-free plants. We were able to clean up 35 lines in the breeding program this way.”
But Douches admits that removing PVS (potato virus S) is challenging. “We’ve been able to remove the virus from 13 lines for other programs,” he said. “That’s 48 lines we’ve cleaned up over the past couple of years with this method. This is a tremendous improvement over what we did in the past.”
A new greenhouse facility was constructed at Michigan State University in 2015; half of which is used for the potato breeding program and the rest devoted to certified seed production. “In our certified seed house, we have nutrient film technique (NFT) for mini-tuber production,” said Douches. “The question is, what size tuber do we want? We try to stay in the 18 to 20 mm diameter. We figure that we can’t push the size down too small. We want to make sure people who buy our seed get good production.”
Douches believes the hydroponic system is the most cost-effective way to produce greenhouse mini-tubers. “For the past few years, we’ve had the certified greenhouse, so we have a relationship with seed organizations that are producing mini tubers and getting them certified,” he said. “We’ve been able to establish the tissue culture lab. We’ve also had a virus eradication system in place.”
The tissue culture bank, which has been in existence for many years, maintains nearly 2,000 potato lines. The material is virus-screened, and much of the material is fingerprinted in order to check the identity.
Douches emphasized the goal of the breeding program: to bring specialty varieties to market.
Potato breeding program benefits growers and consumers
by Sally Colby