Challenges for Agriculture and Food Production:

Understanding Plant Pathology

Timothy Murray

Washington State University

Sustainable Food Security in ASEAN – Role of Genetics and New Technologies

Singapore, 5 September 2016 Kuala Lumpur, 7 September 2016

Ongoing Plant Disease Epidemics

Banana –100 million tonnes/yr in 120 countries

17 Aug 16: “Bananas could be extinct in five years because of a fast-advancing disease compound” news.com.au

Sigatoka complex

20 April 16: “There's a global banana crisis” CNNMoney(London)

Panama Disease, Tropical Race 4

21 May 12: ““Banana AIDs” threatens social fabric on Idjwi island” irinnews.org

Xanthomonas wilt

loe.org apsnet.org

Sally Miller

Ongoing Plant Disease Epidemics

Citrus greening/ Huánglóngbìng - worldwide problem

PD-USGOV-USDA-ARS

apsnet.org

Ongoing Plant Disease Epidemics

Citrus greening/ Huánglóngbìng - worldwide

Coffee Rust

- Central America

Wheat Stem rust Ug99 - east Africa

apsnet.org apsnet.org

Ongoing Plant Disease Epidemics

Citrus greening/ Huánglóngbìng - worldwide

Coffee Rust

- Central America

Wheat Stem rust Ug99 - east Africa

fao.org

Limit losses to all diseases to 5% = $228 million doesn’t include the cost of protection Worldwide losses estimated @ $220 billion*

Impact of Plant Diseases

Crop Value,

$million USD

# Diseases

U.S. WA

Apples 1,386 193 60 Wheat 626 87 39 Potatoes 562 145 59 Hops 89 20 9

Totals $2,663 445 167 All WA Crops $4,566

Limit losses to all diseases to 5% = $228 million doesn’t include the cost of protection

*Soc. Gen Microbiology, April 2011

Pathogen Plant

Environment

‘Disease Triangle’

Resistance Susceptibility

Virulence Pathogenic

specialization

Temperature Moisture

Disease

Causes of Plant Disease

Biotic = transmissible - Fungi - Protozoa - Viruses - Bacteria - Nematodes - Viroids - Phytoplasmas - Parasitic plants

Abiotic = nontransmissible - Heat or cold damage - Too much, to little or

uneven water supply - Unfavorable soil pH - Nutrient deficiencies - Air pollutants - Pesticide damage

More fungal pathogens than any other group, but all have some that are very important and damaging

Drivers of Future Epidemics

Globalization • The world is smaller in terms of the time it takes to

reach distant places, leading to rapid appearance of new diseases & pests in areas

24 hr air traffic among airports worldwide

openflights.org

Drivers of Future Epidemics

Globalization • Pathogens and plants move around the world in

plants, seeds, vegetative propagating material (cuttings) and contaminants on clothing

e.g. Coffee rust introduced into the western hemisphere on infected plants and stripe rust into Australia on clothing

Global monitoring of disease and communication among regulatory agencies and scientists is critical fao.org

Drivers of Future Epidemics

Evolution & adaptation - Genetic changes

that lead to new races e.g. wheat stem rust Ug99

Drivers of Future Epidemics

Evolution & adaptation - Genetic changes

that lead to pesticide-resistant pathogens

plantpath.cornell.edu/labs/mcgrath

waaesd.org/management-of-pesticide-resistance

Drivers of Future Epidemics

Climate change • Warmer/cooler temps

• More intense dry periods/drought

• More intense precipitation events

• Unstable seasonal rains

• Crop production moves northward

Uncertain future except that climate will continue to change

unfccc.int/meetings/paris_nov_2015

Disease Management

How do we limit the impact of plant diseases? • Use a multi-pronged approach as opposed to a

single practice or “Silver-bullet”, which are often effective for only short periods of time Integrated Pest / Disease Management (IPM)

Effective management requires: • Accurate diagnosis • Timely application of management practices

Disease Management Principles

Exclusion Try to keep pathogens from entering areas where they don’t occur • Legal regulation of

movement of agricultural products = Quarantines & Embargoes

ediblegeography.com/landscapes-of-quarantine/

justalittlefurther.com

Disease Management Principles

Exclusion Inspections before or during transit, or upon reaching port of entry • Infested products may be

rejected, destroyed or treated to remove the pathogen or pest

Widely used around the world by most countries

Disease Management Principles

Eradication

Eliminate pathogens from areas where they already occur

• Involves Cultural, Physical & Biological methods

Cultural: any practice having to do with crop management

- commonly includes planting dates, crop rotations, tillage, cleaning equipment, and removal of infected plants or plant parts

Eradication Programs

Barberry eradication

- US from 1917-1981 - 400 million barberry bushes

destroyed

Citrus Tristeza eradication

- 274,000 ha of California citrus tested for CTV beginning in 1963

- infected trees removed and growers compensated

Disease Management Principles

Eradication

Physical methods: use of barriers, heat, or chemicals to destroy pathogens

- common methods include cultivation under glass or screens to exclude insects transmitting pathogens, heat treatment and fumigation

Biological control: use of an organism, genes or gene products to benefit crop production

- introduced microorganisms most common, but also includes inducers of plant resistance

Physical Control

Tomato spotted wilt

- peppers cultivated with clear mulch have reduced disease

Mangoes

- hot water treatment to eliminate fruit flies before import

mangosa.com

Biological Control

Crown gall

- Agrobacterium tumefaciens modifies the plant to begin growing autonomously

- Roots of seedling plants are dipped in a suspension of a related bacterium that prevents it from infecting the plant

- A model system for natural genetic engineering

Biological Control

- Research in early stages; made possible by low-cost nucleic acid sequencing and high-speed computing

A systems approach to improving crop productivity

The “Phytobiome”

- consists of plants, their environment, and the associated communities of organisms in, on and around the plant

Disease Management Principles

Protection

Prevent pathogen from infecting plant

- Most commonly achieved by application of pesticides to growing or harvested product

Evolution of products: contact, broad-spectrum, long-lived to systemic, narrow-spectrum, shorter-lived (environmentally

friendlier)

Greater potential for resistance

Resistance to Pesticides

Need to manage pesticide use to avoid or delay onset of resistance

Kaufmann and Cleveland, 2007

Disease Management Principles

Disease Resistance

Develop plants that are genetically able to reduce activities/damage caused by a pathogen

•Historically based on naturally occurring genes present in crop species or their relatives

a cornerstone of IPM

•High-throughput, low-cost sequencing has resulted in new approaches to speed the traditional breeding process with more predictable results

Disease Resistance

•Advances in biotechnology enable movement of genes between species, transgenics, within the species, cisgenics, and from the pathogen = Pathogen Derived Resistance

•New advances in gene-editing technology (CRISPR/Cas9) allow precise changes enabling control diseases for which control has been difficult

Chandrasekaran, Mol Pl Path 2016

Cucumber with multiple virus resistance

Resistance

Papaya Ringspot Virus

•Devastating to the Hawaiian papaya industry

apsnet.org

apsnet.org

Resistance

Inserting part of the virus genome into papaya allowed it to resist the effects of the virus

apsnet.org apsnet.org

apsnet.org

Questions?