Bacteria, Bioterrorism, and Geraniums

1
Bacteria, Bioterrorism, and Geraniums
2

• Bacteria, Bioterrorism, and Geraniums
• What is a Select Agent plant pathogen?
• Introduction to bacterial wilt and Ralstonia
  solanacearum its impact, pathology and
  epidemiology
• Unintended consequences the geranium outbreaks,
  research, and developing world agriculture
• Select Agent classification revisited

3
The Agricultural Bioterrorism Protection Act
currently lists 8 plant pathogen Select Agents,
pathogens that pose a severe threat to U.S.
agriculture What traits should a plant pathogen
possess if it must be listed as a Select Agent?
4

• Select Agent Plant Pathogens (2008)
• Peronosclerospora philippinesis (sugarcane downy
  mildew)
• Phoma glycinicola (soybean red leaf blotch)
• Ralstonia solanacearum, race 3, biovar 2 (potato
  brown rot)
• Rathayibacter toxicus (ryegrass toxicity
  gumming)
• Scelrophthora rayssiae var. zeae (brown stripe
  downy mildew of corn)
• Synchytrium endobioticum (potato wart)
• Xanthomonas oryzae (bacterial blight of rice)
• Xylella fastidiosa (citrus variegated chlorosis
  strain)

5
Bacterial Wilt Disease
-soilborne, vascular pathogen - single most
destructive bacterial disease in the
tropics Hosts include tobacco, pepper, peanut,
tomato, banana, ginger, potato eggplant
6
Bacterial Wilt Disease
Symptoms -chlorosis -stunting -va
scular browning -wilting -rapid death

• Symptoms
• Yellowing
• Stunting
• Vascular browning
• Wilting
• Rapid death

7

• Ralstonia solanacearum
• - A soilborne bacterium in ß-proteobacteria
  (family Burkholderiaceae)
• - Gram-negative rod with 1-5 polar flagella
• - Optimal growth temperature is 28 C (83 F)
• Doesnt grow well in soil
• Survives in water, soil, and latent host plants
• Does not form spores (resting structures)
• Is not airborne

8
Control of Bacterial Wilt Disease is
Difficult - chemical control (soil fumigation)
is impractical - R. solanacearum survives well
in water and soil - many weed/native plant
hosts - R. solanacearum forms latent
(symptomless) infections - fallowing lt 5 years
largely ineffective - best strategies -
breeding for resistance - clean seed/cuttings
for vegetatively propagated crops (bananas,
plantains, potatoes, ginger, ornamentals etc.)
9
R. solanacearum is divided into 3 races based on
host range
Race 1 broad host-range tropical
strains tomato, peanut, eucalyptus, tobacco, etc
etc
Race 2 banana and plantain strains cause
Moko/bugtok
Race 3 cool-adapted strains cause potato brown
rot many latent weed ornamental hosts (like
geranium)
10
Potato Brown Rot (Race 3, bv2)
- Infected seed tubers, soil, water spread
pathogen - Control exclusion pathogen-free
seed - Many other hosts, e.g. tomato, eggplant,
geranium, nightshade weeds - this race not yet
in N. America, quarantine pest
11

• Global Impact of Potato Brown Rot
• - Caused by R. solanacearum Race 3, Bv 2
• A top 5 potato disease up to 85 losses
• Over 950 M/year in losses in tropics

- Affects 3 million families in 80 countries -
Incidence rapidly increasing in Africa, Asia,
S. America
12

• Potatoes are a key carbohydrate
• crop in the highland tropics
• Little research is done on brown rot

13
Discussion question Given the global impact of
brown rot, should the US government list R.
solanacearum R3bv2 as a bioterrorism agent? If
you were a government agency scientist, what data
would you need to decide whether to list R3bv2 as
a Select Agent?
14
Brown rot in Europe
15
1995 Significant European Brown Rot -Unusually
hot summer -Outbreaks on 25 scattered seed and
ware farms in Holland -Several cultivars
affected -Dutch blame Egyptian starch
potatoes -Italy, France, and UK also eventually
report outbreaks (they blame Dutch seed
potatoes) - Retrospectively, it appears both
water seed tubers contributed. Pathogen
probably there since 1989
16
1997 Official EU Control Directive
to -determine extent of pathogen
distribution -contain outbreak -eventually
eradicate the bacterium Director of Dutch Seed
Potato Federation Eradication is a good option
for brown rot in the Netherlands. BUT.
17
Research reveals that -R. solanacearum Race 3
can survive 2 years in temperate soil. - R.
solanacearum Race 3 can survive indefinitely in
surface water. - latent hosts like stinging
nettle bittersweet nightshade (S. dulcamara)
hold large populations. -R. solanacearum becomes
VBNC in response to cold or copper. -Still
present in Dutch canals after 10 years.
18
By 2002 Brown rot reported in Belgium,
Denmark, France, Germany, Greece, Italy, the
Netherlands, Portugal, Spain, Sweden, and the
UK HOWEVER outbreaks are minors sporadic.
No significant losses to brown rot disease EU
microbial ecology consortium declares R.
solanacearum endemic, recommends abolishing
quarantine eradication program
19
Given these facts, does Ralstonia solanacearum
race 3 biovar 2 qualify as a Select Bioterrorism
Agent?
20
Brown rot disease has historically not
affected potatoes grown in cool temperate
climates (winter temperatures below -5C). The
pathogen can not be efficiently spread by
spraying. Brown rotted potatoes are not toxic to
humans. Is this a tool a terrorist would choose?
How scary is a potato disease?
21
Is brown rot a threat to the US potato industry?
(conducive environment)
Disease Triangle
susceptible host
(pathogen)
22
Another factor The US-Canadian Potato Wars A
long history of blocking each others potato
imports based on discovery of quarantine
pests 1980 Canadians have potato golden
nematode (US blocks Canadian potatoes) 1990 US
gets potato golden nematode (blocks
dropped) 1994 US has potato virus Y (Canada
blocks US potatoes) 2001 Canada has potato
wart (Synchytrium endobioticum) (US blocks
Canadian potatoes) R3bv2 is a quarantine pest in
both countries
23
Should economic protection of a crop market be a
consideration in listing a pathogen as a Select
Bioterrorism Agent?
24
December, 2002 R. solanacearum Race 3 was
listed as a potential bioterrorism Select Agent
in the Agricultural Bioterrorism Protection Act
of 2002, mandating strict new biosecurity and
quarantine regulations.
25

• Select Agent Regulations
• All researchers (including students) must undergo
  Dept of Justice personal background checks and
  regular training, reporting
• Shipment and storage of Agent only under highest
  physical security
• Mandates exhaustive record-keeping, monthly
  inventories, spot inspections, visitor logs, etc.
• Research in separate lab with videosurveillance,
  fingerprint access locks, duplicated equipment

26
February 2003 R. solanacearum R3bv2 discovered
on N. American geraniums
27
R. solanacearum bacterial wilt symptoms on
geranium
J. Janse
J. Janse
-wilting leaves -yellowed leaves -necrotic wedges
on leaves -vascular browning in
stem -eventual collapse death
J. Janse
J. Janse
28
(No Transcript)
29

• February, 2003
• Growers report wilting Wisconsin geraniums
• - We determine pathogen is RsR3bv2, tell USDA
• - FBI calls

30
Impact of February 2003 Outbreak - Hold orders
placed on over 1000 greenhouses - Neither
diagnostics nor Action Plan in place - RsR3Bv2
found in 127 facilities in 27 states Cost 6M in
crop losses, 880K in regulatory costs
31

• December 2003, Ralstonia Round 2
• - Geraniums with Southern wilt detected in one
  New York greenhouse
• Company has no traceback ability USDA
• issues destruct orders for all 2 million
  geraniums of
• suspect varieties shipped from Guatemala since
  August
• 458 greenhouses in 41 states are affected
• - Cost over 4 million

32
March 2003 Goldsmith plants goes under. 1200
Kenyan and Guatemalan workers lose their jobs
33
Bacterial wilt has disproportionate impact on
small growers in the developing tropics, where
there is little research capacity
34
Select Agent regulations impede or prevent US
researchers working to control bacterial wilt in
the developing tropics