At typical Thanksgiving meals in Louisiana, sweet potatoes can be found baked under layers of marshmallows or brown sugar and pecans. These dishes still qualify as vegetable sides; the nutritious orange flesh of the sweet potatoes more than atones for the sugary toppings. Sweet potatoes also find their way into bona fide desserts, as in sweet potato pie that will shut your mouth. Before the insulin shock sets in for any of these sweet potato offerings this week, let’s dig a little deeper into the plant behind the plate.
First, what’s in a name? Would a potato by any other name be as sweet? Well, no and yes. Sweet is the only thing true about the sweet potato name. Sweet potatoes are only distantly related to regular potatoes. Sweet potatoes are actually more closely related to morning glories. And for the record, yams are yet another vegetable altogether. Yams are even further removed from both potatoes and sweet potatoes. Louisiana started marketing their sweet potato varieties under the ‘yam’ name as a ploy to distinguish themselves from the competition back in 1937.
More than 130 000 acres of sweet potatoes were planted in the United States last year with the top-producing sweet potato states being North Carolina, California, Mississippi and Louisiana. Needless to say, that’s no small potatoes. Of course, per capita sweet potato consumption has declined over the last century (4 pounds annually today compared to 30 pounds annually in 1920). Even so, for Louisiana the sweet potato industry is a $100+ million business, and the state’s leading vegetable crop. To support the state’s sweet potato business, Louisiana has a Sweet Potato Research Station dedicated to breeding new varieties and providing disease-free seed for Louisiana growers.
Louisiana has traditionally pushed the boundaries of sweet potato production. In the early 1900s, the Louisiana Agricultural Research Station released the Unit 1 Porto Rico variety developed by Julian C. Miller. Its revolutionary characteristic- moist, orange flesh. In 1987, Dr. Larry Ralston released the Beaureguard variety that maintained the sweet rich flavor of the Porto Rico, but had increased insect- and disease- resistance. It is still the main sweet potato grown in the state, but the research station is continually churning out new varieties with better yields or other advantageous traits. Be on the lookout for the LA 07-146, which out-produces the Beaureguard and has sweeter flesh. Currently it is grown for the processing sector and not for the supermarket because it has a red skin that may put off some consumers. I’m sure that some creative renaming of the LA 07-146 would do wonders for its appeal in the supermarket.
In addition to developing new varieties, the Sweet Potato Research Station is also charged with maintaining the genetic integrity of the stocks used by the state’s growers. Before getting into those scientific details, I recommend checking out this short video from the LSU AgCenter about sweet potato production in Louisiana.
As you may have noticed from the video, sweet potatoes are not grown from seed. They are grown from seed potato stocks until plantlets called ‘slips’ grow out of them. When these slips are 10 – 14 inches, they are cut away from the seed potatoes and transplanted into the rows for production. This is a type of vegetative propagation, meaning that all of the plants that develop are (in theory) genetically identical to the seed potatoes used. During the production phase, there is no opportunity for the reshuffling of genetic material that sexual reproduction offers. Because of this, growers must beware of genetic defects that sneak into their seed potatoes from viruses and other pathogens. These defects have the potential to decrease the yields of subsequent crops and change the overall quality of the potatoes produced. One way the Sweet Potato Research Station combats this industry problem is to provide virus-tested foundation seed to growers. Sweet potato growers start with this foundation seed for their on-farm seed programs.
This foundation seed is developed from a virus-tested tissue culture approach to ensure that the tissue used is free from viral pathogens. In this process, very small pieces (less than 0.5 mm) of plant tissue are removed from a plant. This piece can be converted into a whole new plant through plant tissue culture, which undergoes thorough testing to verify that it is free from viruses. The testing is a labor-intensive process and ultimately the newly regenerated and tested plant must still be grown in the field to make sure that the sweet potatoes maintain their original characteristics. The revenue generated from selling this foundation seed to growers is used to fund itself and other initiatives at the research station.
Now when you sit down to your Thanksgiving table, you can ask for your sweet potatoes by name or at least impress your family and friends with interesting sweet potato factoids. Feel free to use any of this info (and more on the links below) to divert the dinnertime conversation away from possibly sensitive subjects like “When are you getting married? When will you graduate? Are you having any (more) kids? Postdoc, huh. Is that a real job?” At the very least, you can be thankful that there are growers and scientists out there that care about sweet potatoes more than you could ever imagine, and that’s pretty sweet.