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