Feast or Fungus

Genetically engineered potatoes resist fungal diseases

Yesterday's science fiction is today's reality. Advances in biology — especially in the field of genetic engineering — allow scientists to safely do marvelous things that were only dreamed of a few short years ago. Nowhere is this more evident than in the food production industry. Scientists now can engineer the genetic makeup of plants to make them grow bigger and better than ever before, without the use of chemical pesticides and fertilizers. What's more, they are devising ways to give these plants natural resistance to disease and insect pests.

The potato is a good example. The potato is the fourth most widely used world food crop, after wheat, rice, and corn. In Colorado, besides being an important fresh market crop, potatoes are a $25 million seed crop. But potatoes historically have been susceptible to fungal diseases. In fact, history records that potato fungal diseases have been responsible for starvation, death, and mass immigration. A hundred and fifty years ago, potato blight was the main cause of the infamous Irish Potato Famine. Potatoes were a main staple of the Irish diet. When the crop failed, millions died. Millions more immigrated to America and Europe to avoid the same fate.

Colorado potato producers annually lose around $15 million to potato blight. Most serious are early blight and late blight, diseases that attack leaves and flesh of the potato, leaving it unusable for consumption or seed stock.

Colorado State University associate professor of biology Anireddy S.N. Reddy is a researcher whose goal is to engineer potato genetics to produce varieties that naturally resist fungal diseases. The traditional way to do this is to crossbreed varieties of potato plants that produce good potatoes but may be susceptible to disease with naturally disease-resistant wild varieties to produce offspring with some of the traits of both. By crossing the offspring with other disease-resistant varieties, the.resistance is enhanced. The obvious drawbacks to the method are time, accuracy, and compatibility of varieties. First, you must identify plants with the desired traits and then get them to crossbreed successfully. Then, you wait to see what happens. After years of crosses, the eventual outcome is, hopefully, a variety of plant with the desired traits. Reddy has a better method.

Reddy manipulates the genetic makeup of potato cells to produce new disease-resistant varieties. To do this, he looks for genes in the plant and animal kingdom with the properties he needs. He isolated genes from certain mustard plants and from Drosophila, an insect that produces proteins capable of stopping the growth of fungal pathogens. He introduced these genes into potato cells in a way that would make the cells overproduce fungal growth-inhibiting proteins. The result was four new lines of potato plants, each capable of producing a different type of antifungal protein.

The new plants were tested for resistance to common potato fungal diseases. One was found to have resistance to early blight. The other types are being analyzed for additional disease resistance. Reddy hopes to develop a potato line that overproduces more than one antifungal protein to increase disease resistance against a broad spectrum of fungal pathogens.

Reddy is quick to point out that even though he's made progress, there's much more work ahead. Several generations must be grown to determine how effective disease resistance will be. Also, Reddy intends to enhance his disease-resistant potato varieties with qualities desirable to consumers, such as good flavor, texture, and color. For the farmer, good yields are important, too. "This will take time," says Reddy. "But what's exciting is the potential to make a better product with more naturally disease-free potatoes in the bag without the high costs and environmental impacts of traditional chemical controls."