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
Ongoing Plant Disease Epidemics
Banana
Citrus greening/ Huánglóngbìng
- worldwide problem
–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
apsnet.org
loe.org
PD-USGOV-USDA-ARS
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
apsnet.org
Sally Miller
Ongoing Plant Disease Epidemics
Ongoing Plant Disease Epidemics
Citrus greening/ Huánglóngbìng
- worldwide
Coffee Rust
- Central America
Wheat Stem rust Ug99
- east Africa
Citrus greening/ Huánglóngbìng
- worldwide
Coffee Rust
- Central America
Wheat Stem rust Ug99
- east Africa
apsnet.org
fao.org
apsnet.org
‘Disease Triangle’
Impact of Plant Diseases
Crop
Apples
Wheat
Potatoes
Hops
Totals
All WA Crops
Value,
$million USD
1,386
626
562
89
$2,663
$4,566
# Diseases
U.S.
WA
193
60
87
39
145
59
20
9
445
167
Limit losses to all diseases to 5% = $228 million
doesn’t include the cost of protection
Worldwide losses estimated @ $220 billion*
*Soc. Gen Microbiology, April 2011
Temperature
Moisture
Environment
Resistance
Susceptibility
Virulence
Pathogenic
specialization
Disease
Plant
Pathogen
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
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
 More fungal pathogens than any other group, but all
have some that are very important and damaging
openflights.org
24 hr air traffic among airports worldwide
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
Drivers of Future Epidemics
Evolution &
adaptation
- Genetic changes
that lead to
new races
e.g. wheat stem
rust Ug99
fao.org
Drivers of Future Epidemics
Drivers of Future Epidemics
Climate change
Evolution &
adaptation
Warmer/cooler temps
More intense dry
periods/drought
• More intense precipitation
events
• Unstable seasonal rains
• Crop production moves
northward
•
•
- Genetic changes
that lead to
pesticide-resistant
pathogens
unfccc.int/meetings/paris_nov_2015
waaesd.org/management-of-pesticide-resistance
 Uncertain future except
that climate will
continue to change
plantpath.cornell.edu/labs/mcgrath
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
justalittlefurther.com
ediblegeography.com/landscapes-of-quarantine/
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
Eradication Programs
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
Disease Management Principles
Barberry eradication
Eradication
- US from 1917-1981
- 400 million barberry bushes
destroyed
Physical methods: use of barriers, heat, or chemicals
to destroy pathogens
Citrus Tristeza eradication
- 274,000 ha of California
citrus tested for CTV
beginning in 1963
- infected trees removed and
growers compensated
- 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
Biological Control
Tomato spotted wilt
- peppers cultivated with
clear mulch have reduced
disease
Mangoes
- hot water treatment to
eliminate fruit flies
before import
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
mangosa.com
Biological Control
The “Phytobiome”
- consists of plants, their
environment, and the
associated communities of
organisms in, on and around
the plant
- Research in early stages; made
possible by low-cost nucleic
acid sequencing and highspeed computing
A systems approach to
improving crop productivity
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
Disease Management Principles
Disease Resistance
Kaufmann and Cleveland, 2007
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
 Need to manage pesticide use to avoid or
delay onset of resistance
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
Resistance
Papaya Ringspot
Virus
• Devastating to the
Hawaiian papaya
industry
Cucumber with
multiple virus
resistance
apsnet.org
apsnet.org
Chandrasekaran, Mol Pl Path 2016
Resistance
Questions?
apsnet.org
Inserting part of the virus genome into papaya
allowed it to resist the effects of the virus
apsnet.org
apsnet.org