Learning from Past and Current Plant Epidemics This slide show was adapted from a December 2003 presentation by James Schoelz, Ph.D., at the Missouri Summit on Agroterrorism. Schoelz is Professor and Chair of the Department of Plant Microbiology and Pathology at the University of Missouri-Columbia. Case Studies, ramifications, and emerging strategies for combating plant diseases

Presentation Overview Learning from Past Epidemics Case Study: The Potato Famine of Ireland Case Study: Southern Corn Leaf Blight 1970 Threats to the US Disease categories New pests and pathogens Scenario: Soybean Rust State of the Art Strategies for Combating Plant Epidemics

Sources: Encyclopedia Britannica, 2002; Pictorial Times, 1846 Case History: The Irish Potato Famine almost half of the population in Ireland depended on potatoes to survive. In the 1840s,

Sources: Encyclopedia Britannica, 2002; Illustrated London News, 1849 The Irish Potato Famine-- continued In order to feed its people, Ireland relied primarily upon two high-yielding potato varieties. When the potato disease struck, it resulted in a massive crop failure that lasted five years,

Due to the crop failure... …thousands resorted to begging for food… …there were food riots… … and many were evicted, and their homes were burned. Sources: Encyclopedia Britannica, 2002; Illustrated London News, 1842, 1848; LLDB, 1847

Sources: Plant Diseases: Their Biology and Social Impact; Encyclopedia Britannica, 2002; Illustrated London News, 1847; 1851 A loss of 1 million lives due to starvation and disease. A loss of 1.5 million due to emigration. Ireland’s 1845 population of 8 million dropped to 5.5 million by Over a 15 year period in Ireland...

A disease, called Late Blight of Potato destroyed both the leaves and tubers of the potato plants. The cause was a fungus called Phytophthora infestans What caused The Irish Potato Famine?

Why was the disease widespread? An environment conducive to disease Uniform susceptibility in the host plants The introduction of a pathogen Three factors:

Need a more recent case study? Let’s look at the 1970 Southern Corn Leaf Blight Epidemic In 1970, 80% of all hybrid field corn grown in the U.S. was susceptible to Southern Corn Leaf Blight.

Southern Corn Leaf Blight Epidemic -- continued The pathogen introduced was Cochliobolus heterostrophus race T

A. June 18 B. July 15 C. September 1 The generation time for new inoculum? Only 51 hrs Source: Plant Diseases: Their Biology and Social Impact The path: Progress of Southern Corn Leaf Blight Epidemic in North America (1970)

Why did it happen? An environment conducive to disease Uniform susceptibility in the host plants The introduction of a pathogen

The consequences? Over $1 billion in losses In many southern states, entire fields were lost Losses of % were common Source: Plant Diseases: Their Biology and Social Impact

Part Two Categories of Plant Diseases Recently-introduced pests and pathogens Scenario: Is a Soybean Rust Epidemic in our Future? Plant biosecurity threats to the U.S.

5 Categories of Plant Diseases 1. New Disease – introduced on new host within last five years in a new geographic area 2. Emerging Disease – increased incidence within last years 3. Re-emerging disease - previously known in area but gaining importance 4. Threatening Disease – not reported or limited distribution in a new geographic area 5. Chronic/spreading disease - known for a long period and still causing out breaks. Sources: SPDN; Damsteegt (1999)

Can you list an example of an emerging plant pest or pathogen that has been introduced in the United States after 1990, but is not yet eradicated? Question:

Examples of new pests and pathogens introduced in U.S. since 1990 Source: APHIS/PPQ Pest or pathogenSusceptible CropsState Citrus canker Xanthomonas axonopodis pv. citri Orange; grapefruit; key lime; sweet lime; lemons; orange; tangelo; kumquat; pineapple FL 1999 Plum pox virus (sharka) Plum pox potyvirus (PPV-D) Peach; apricot; cherry; plum nectarine; almonds PA 1999 Glassy-winged sharpshooter, a new carrier (vector) of Pierce’s Disease Xylella fastidiosa Grapes (includes the raisin and wine industries) CA 1990

Depending on the plant species and pest or pathogen, these outbreaks may be spread by: Aphids and other vectors (carriers) Propagation of diseased plants Planting of infected seeds Contaminated cattle manure Crops moved in contaminated equipment Wind, including hurricanes & tornadoes Human transportation of infected plants and fruits (intentional and unintentional)... and other methods

Losses associated with select pests and pathogens and their status in the U.S.: Sources: APHIS/PPQ and APS Society Pest or pathogenLossesStatus Citrus canker Xanthomonas axonopodis pv. citri 2.3 million commercial trees destroyed by Dec ,219 residential trees destroyed Jan 2001 $145 million spent on eradication in 2000 Eradicated in 1910 and Current FL eradication program started in Quarantines in 13 areas Plum pox virus (sharka) Plum pox potyvirus (PPV-D) 900 acres of tress destroyed and burned Quarantines in PA; ongoing surveys Glassy-winged sharpshooter, a new carrier (vector) of Pierce’s Disease Xylella fastidiosa Multi-million dollar losses to grape industry. CA statewide plan implemented

Can you list a soybean plant pest or pathogen that has NOT YET been introduced in the continental United States, but for which we are “at risk?” Question:

Answer: Soybean Rust Soybean Rust is NOT present in the continental U.S., but is found in every other major soybean-growing area in the world. Source: Soybean Rust: Is the U.S. Crop at Risk, APSnet feature, Soybean Rust is caused by the fungi Phakopsora pachyrhizi and P. meilbomiae

This chart depicts the exponential spread of a soybean rust epidemic in a field. Soybean Rust-- continued Once introduced, soybean rust could spread rapidly as the generation time for new inoculum can be as little as 9 days and in the U.S., there is little variation in cultivars. Source: SASPP.org 2002

The epidemic may readily spread across the U.S., as the rust spores are carried by wind to new areas. The “Puccinia Pathway” Stem rust of the spores survive the winter in Mexico and each year are blown northward to Canada. (It is likely that similar winds carried soybean rust from Asia to South Africa). Soybean Rust -- continued Source: SASPP.org 20002

Lima bean Butter beanGreen bean CowpeaLupineSweet Clover... and Kudzu Further, over 30 legume species may serve as alternate hosts for soybean rust, including Soybean Rust -- continued

Question: Could a soybean rust epidemic occur? Would the environment be conducive to disease? Is there uniform susceptibility in host plants? Is a pathogen present? If the soybean rust fungi were introduced, the answer would be yes, an epidemic could occur.

If established in main soybean production areas, losses could be % A 1984 economic risk analysis predicted total potential losses of $7.1 billion Source: Soybean Rust: Is the U.S. Crop at Risk APSnet feature, 2003 If an epidemic occurred in the U.S., the potential ramifications are: Soybean Rust -- continued

What strategies are being used to keep soybean rust out of the United States? Question: Soybean Rust -- continued

Current Strategies to Manage Soybean Rust Immediate strategy: Fungicides Longer term strategy: Resistance However, no commercial cultivars in the U.S. have resistance, although a resistant germplasm has been identified in other parts of the world.

Part Three Currently-available protection and control strategies Emerging plant protection and control strategies State of the Art Plant Biosecurity Strategies for combating natural and man-made epidemics

Protection and Control Strategies Field, orchard, and vineyard quarantines Fungicide treatments Biological control such as insects, pathogens, and/or nematodes Destroy infected fields, orchards, and vineyards Disinfect equipment and storage facilities Depending on the plant pest or pathogen, strategies spread might include:

In the future, producers may also have access to Emerging Plant Protection Strategies Novel strategies for disease resistance Accurate and reliable sensing technologies Cultivars bred for resistance to threatening diseases Plants genetically-manipulated for natural resistance

Conclusion Past epidemics teach us strategies for combating new pests and pathogens: Environments conducive to disease Uniform susceptibility of host plants Introduction pests or pathogens Several emerging and novel strategies for combating plant epidemics are on the horizon New pests and pathogens have been introduced; still others threaten the U.S.

Presentation References  Schoelz, J. (2003, December). What can we learn from past and current epidemics of plants? Paper presented at the Missouri Summit on Agroterrorism. University of Missouri, Columbia, MO.  Southern Plant Diagnostic Network. (2004). Disease categories. Retrieved from the University of Florida

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