Editor’s note: This year is 2020 is the International Year of Plant Health, as designated by the UN. Agronomists, crop, and plant scientists work to develop disease-resistant varieties and to track the path of deadly plant pathogens. This helps keep our crops and plants free from disease and ensures a healthy food supply. Visit https://www.aphis.usda.gov/aphis/ourfocus/planthealth/iyph/iyph2020 to learn more about the different themes developed to celebrate this year. August’s theme is Breakfast!
What do you look forward to in the morning? A cup of tea? Coffee? What about cereal, or toast with jam? Around the world, families eat various foods for breakfast – and all those foods have a constant threat over them. If plant diseases are not managed properly, our breakfast tables could be vastly different.
Globally, wheat is in breakfast dishes in several forms: breakfast cereal, bread, pancakes, muffins, flatbreads, tortillas, breakfast burrito, etc. Many cultures in the world have a donut variation including Beignet (France), Sufganiyot (Israel), Balushahi (India), Buñuelos (South America), Mandazi (East and Central Africa) among others.
One of the biggest threats to global wheat supply is the disease wheat stem rust. This fungal disease dates to the Roman Empire. Infections can be seen by spots on the stem and leaves that have rust-colored powdery spores in them. These spots affect the plant by reducing the plant’s ability to photosynthesize. This reduces the number and size of the wheat kernels.
This disease is managed by the development of resistant varieties. However, every few decades a new strain appears that the currently grown varieties do not have resistance to. In 1999 a new fast-spreading strain of the fungus was detected in Uganda called Ug99. It devastated yields and reduced the milling quality of the grain. Rust spores can travel long distances, spreading the disease quickly throughout Africa and the Middle East. Currently, it threatens to wipe out more than 80% of existing varieties. Food security in developing countries is largely dependent on wheat. With other key crops such as cassava being threatened by a virus, stopping Ug99 is vital. Scientists are working on breeding resistant varieties to save this precious grain.
Coffee rust is caused by a fungal pathogen very similar to the wheat stem rust fungus. The leaves develop yellow spots that spread and eventually join. Dust-like spores are formed and spread by both wind and water to other plants. If those plants are susceptible, new infections are formed. Prior to 1869, the island British colony Ceylon (modern-day Sri Lanka) was the largest producer of coffee in the world. Coffee, rather than tea, was the drink of choice in high society. This ended when a major outbreak of coffee rust devastated coffee plantations in Sri Lanka. Coffee production eventually migrated to South America. Sri Lanka’s coffee plantations were converted to growing tea making it the largest producer of tea in the world. This epidemic is considered the main reason the British drink tea over coffee. Coffee rust is now found in all major coffee-growing regions of the world.
The biggest threat to our daily glass of Florida orange juice is citrus greening disease. Citrus greening is caused by a bacterium transmitted by insects. The symptoms of this disease are yellowing leaf veins and splotchy green patches on ripe fruit. Infected fruit is sour and unusable for consumption. The bacteria have spread throughout the world, infecting many types of citrus trees including oranges, lemons, grapefruit, and limes. Farmers and agronomists first found citrus greening in the United States in 2005. Arriving in Florida, where citrus is a major crop, it quickly spread to most Florida farms.
To combat the spread of citrus greening, the USDA regulated transport of citrus fruits in the US. Despite these regulations, the disease has spread to California, the other major citrus-producing state. There are currently no treatments or resistant varieties available for this disease. Our main strategy for managing this disease is preventing spread by eradicating infected trees and ensuring infected plants are not moved to new regions.
Bananas are a classic breakfast fruit for many people around the world. In the world, bananas are considered one of the top 10 staple crops; in rural Africa, bananas can count for 25 percent of daily caloric intake. Bananas under threat from a devastating disease, known as Fusarium wilt. This disease completely wiped out a variety of banana called Gros Michel banana in the mid-1900s and shifted the market dominance to the Cavendish cultivar.
Banana cultivation is a monoculture, meaning they are grown only with other bananas. They are not grown from seeds, as their seeds are sterile. New shoots come up every year in healthy plants to provide a new crop. If new banana plants are needed, they must be reproduced through cloning propagation. That means every banana is genetically identical to the one next to it.
The Cavendish cultivar was resistant to the Fusarium wilt fungus when it began to dominate the banana markets. Like many fungal, bacterial, and viral plant infections, new strains of the disease naturally occur over time. A new race of Fusarium, TR4, is attacking the Cavendish cultivar with new vigor in nearly all the banana producing regions. Fusarium enters the plant from the roots and then colonizes the xylem of the plant. As the fungus grows in the xylem, water flow becomes blocked. The plant wilts and eventually dies.
Without proper disease management and continued research, the crops that create some of our favorite breakfast foods are at risk. Resistant varieties, pesticides, eradication programs, and quarantines are all a part of sustainable disease management. While we all do our part to slow the spread of human disease, we should also learn more about the treatment of plant disease to our food systems. 2020 is the International Year of Plant Health, find out more information https://www.apsnet.org/edcenter/disandpath/featuredArt/Pages/default.aspx, or listen to a plant disease podcast at https://www.plantopiapodcast.org/about.
Answered by Claire Poore, North Dakota State University and Mallowa Sally, Augustana University Sioux Falls, SD
About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Our members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting our environment. We work at universities, government research facilities, and private businesses across the United States and the world.
Categories: Food security