A threat to forests and fields

Some plant diseases can drastically alter our environment, or dangerously affect our food supply.

Sprint Blackstem: Spring blackstem and leaf spot are infections caused by the fungus <em>Phoma medicaginis</em>. It kills off leaves or entire alfalfa plants before they can be harvested. Samac and her lab hope to create alfalfa cultivars that are able to fight off pathogens like <em>Phoma</em>.
Sprint Blackstem: Spring blackstem and leaf spot are infections caused by the fungus Phoma medicaginis. It kills off leaves or entire alfalfa plants before they can be harvested. Samac and her lab hope to create alfalfa cultivars that are able to fight off pathogens like Phoma.
Courtesy Deborah Samac

American chestnuts were once one of the most common trees in the forests of eastern North America. In 1904, however, people noticed sick and dying American chestnut trees around the Bronx Zoo. A bark-infecting fungus—chestnut blight—caused the fatal disease, and within forty years it spread across the country, killing billions of trees. Today, there are probably fewer than 100 fully-grown American chestnut trees left in the country.

Plant diseases can also impact important food crops. In the 1800s, the people of Ireland were heavily dependant on potatoes for food. When a deadly water mold was accidentally brought to the island in 1845, the country’s potato crop was almost totally destroyed. The resulting famine contributed to the deaths of over a million people in the following five years.

While techniques for protecting crops from diseases are far better now than in decades past, plant pathologists are always on the lookout for new threats, and are constantly developing more effective methods for battling these plant diseases.

Old ideas, new techniques

Leaf spot
Leaf spot
Courtesy Deborah Samac

Working for the USDA-Agricultural Research Service, Deborah Samac and her lab are finding ways to keep alfalfa from getting sick. Alfalfa is a flowering plant related to peas. People don’t eat much alfalfa, but it’s a potential biofuel crop, and it’s a very important forage plant for the animals we eat. Fungal infections like spring blackstem and leaf spot can harm crop yields, so Samac is working to create a type of alfalfa that is genetically resistant to disease.

People have been genetically modifying plants for hundreds of years by crossbreeding them to bring out certain traits. Scientists are now able insert specific genes quickly and accurately by infecting plants with special bacteria that leave selected genes within the plants’ cells. When the plants reproduce, the next generation will already have traits from these genes. Along with creating disease resistant alfalfa, Samac hopes to produce plants that are more nutritious, and can grow in a wider variety of soil conditions.