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Human Defense Strategy Against this Attack,Problems in Taming CBSVs(Cassava Brown Streak Viruses),New Understanding of Epidemiology,Virus-free Cassava Seed Systems
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Taming the Cassava Virus Monster:
A Research for Development Case Study
James Legg: Review Seminar – IITA-Ibadan, March 22, 2011
CLARFIYING DEFINITIONS
1. A creature of abnormal form or
structure
2. One who deviates from normal or
acceptable behaviour or character
3. A threatening force
4. One that is highly successful
Merriam-Webster Definition
How do you tame it?
1. Stab it through the heart with a knife
Outcome. DEATH (unless it’s a vampire, in which
case you need a wooden stake)
2. Put some fresh cassava leaves in its supper
Outcome. DEATH
3. Infect it with a nasty chronic disease
(preferably a virus) Outcome. WEAKNESS
4. Be extra nice to it (and hope it reciprocates
the favour)
Outcome. UNAFFECTED
Chase it away
Effect of Taming Strategies on Outcomes
for Monsters and Humans
Taming Strategy Also Called Who Wins?
1 (Murder) Eradication Humans
2 (Infection) Mitigation Mainly humans
3 (Friendship) Co-existence Mainly monsters
4 (Chasing) Chasing Monsters Humans
…….but they can look pretty scary…
And together ‘attack’ humans indirectly through
removing ca. 1/3 of all production of one of their
food staples in Africa: Cassava
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Hea
lthy
EACM
V-U
g
EACM
V-U
g+ACM
V
Kg/p
lant
Primarily Strategy 2
Mitigation
Human Defense Strategy Against this Attack ?
Adequate ?
CBSD incidence
2010(GLCI)
Map: Hein Bouwmeester
CBSDincidence
change2009-10
Map: Hein Bouwmeester
How Good has our Taming
been so far?
Cassava Mosaic Geminiviruses (CMGs)
Conventional HPR – virtual immunity
Cassava Brown Streak Viruses (CBSVs)
Limited effort
Promotion of ‘tolerant’ varieties
Cassava Whiteflies
Largely ignored. Virus management perceived
to be more straightforward
Problems in Taming CBSVs
Knowledge. Almost none prior to 2008
Symptoms. Cryptic. Field diagnosis hard
Awareness. Little before late 2000s
One-dimensional. Existing mitigation work
Status of CBSD Knowledge
Element Pre-2008 Post-2008 IITA
1. Partial sequencing S
2. Whole genome sequencing X
3. Confirmation of aetiology X
4. Symptom relationship characterization L
5. Crop loss assessment L
6. Determination of vector X
7. Characterization of transmission L
8. Field-based epidemiology L
9. Regional epidemiology L
10. Development of diagnostics S
11. Molecular markers L
12. Conventional HP tolerance L
13. Transgenic resistance X
Framework for CBSV
Research at IITA
Foundation of support through CORE
GLCI Project (IITA-Ibadan, IITA-Tanzania)
Biotechnology Project (IITA-Kenya)
Malawi CBSV Project (IITA: Tanzania, Ibadan
and Malawi)
167 (
f3/r
3)4
20
8(f
3/r
3)4
217(F
3R
3)2
292 (
F3R
3)1
168(f
3/r
3)4
229(f
3/r
3)4
170(f
3/r
3)4
231(f
3/r
3)4
178(f3/r3)4
21 (f3
R3)1
280
(f3R
3)1
177(
f3/r3)
4
173(
f3/r3)
4
186(
f3/r3
)4
207(
f3/r3
)4
293(f3/r3
)4
318(f3/r3
)4
326(f3/r3
)4
324 (F3R3)1
335(F3/R3)3
275(F3R3)2
243(10-11)2
173(10/11)3
335(10/11)3
209(10/11)3
273 (10/11)3
332(f3/r3)4
181(f3/r3)4273(F3R3)2271(F3R3)2173(F3/R3)3241(F3R3)1138(F3/R3)3243(F3/R3)3261(F3R3)2
250 (F3R3)1
247(F3/R3)3
248(F3R3)2
259(F3R3)2
EU916831 CBSV (BSA2) CP
EU916829 C
BSV (LWR2) C
P
EU916828 C
BSV (H
MA9) C
P
EU916827 C
BSV (N
TG10) C
P
EU
916832 CBSV (B
SA4) C
P
EU
916830 CBSV (IG
A8) C
P
295(f3
/r3)4
296(f3
/r3)4
298(f3
/r3)4
285(F
3/R
3)3
80(F
3R
3)2
EU
916825 C
BS
V (M
LB
3) C
P
FJ039520 C
BS
V-M
LB
Tz
EU
916826 C
BS
V (M
LB
9) C
P
209 (F
3R
3)1
32
8(F
3/R
3)3
33
7(f3
/r3)4
321(F
3/R
3)3
81 (F
3/R
3)3
14 (F
3R
3)1
23(1
0-1
1)2
274(1
0-1
1)2
281 (1
0-1
1)2
138(1
0-1
1)2
43 (F
3R
3)1
137(F
3/R
3)3
269 (F3R
3)1
82 (F3R
3)1
249 (F3R3)1
80 (1
0/11
)3
294(
f3/r3
)4
255(F3R3)2
289(f3/r3
)4
AY008441 CBSV (t
ype B) C
P
314(f3/r3
)4
FN423418 CBSV-Naliendele-2 (Tz
FN423416 CBSV-CP (Naliendele-1 Tz
FN423416 CBSV-Naliendele-1 ( Tz-N
FN423418 CBSV-CP (Naliendele-2-Tz
355(10/11)3357 (10/11)3359(10-11)2354 (10/11)3
355(F3R3)2
354(F3R3)2
357(F3R3)2
AY007597 CBSV CP
AY008440 CBSV (type C) CP
FN423417 CBSV-CP (Nam-Moz)
FN423417 CBSV Nam-Moz
AY008442 CBSV (type A) CP
AF311053 CBSV
FJ821794 CBSV (KBH2) CP
FJ821795 CBSV (KBH1) CP
AF311052 CBSV
356 (10-11)2
358(10-11)2
276(10-11)2
278(10-11)2
353(10/11)3
352(10-11)2
353(F
3R
3)2
279(1
0-1
1)2
280(1
0-1
1)2
FJ795780 S
PF
MV
-ug
0.1
CBSV
Karonga & Rhumpi
UCBSV
All areas
Diversity of CBSVs in Malawi(Slide from Lava Kumar)
70 isolates were analyzed from six districts
Based on 3’ coat protein gene sequence
Neighbor-Joining method; 1000 bootstraps
Reference sequences from GenBank are with accession numbers
CBSV Diagnostics
at IITA-Tanzania
CBSV Diagnostics Validation
CBSV 10/11
CBSV Real CBSV UG
F/R
CBSUV Real
CBSV + + - -
UCBSV-1 - - + +
UCBSV-2 + - + +
CBSV+UCBSV-1/2 + + + +
Tanzania CBSVs detected by primers combination
CBSV 10/11 with CBSV UG F/R detect > 99% real-time +ves
Working with IITA-Ibadan/NRI to add F3/R3, new primers
Putting PCR into practise
PCR underway: ISABU,
Bujumbura, Burundi
PCR results: ISAR,
Ruhengeri, Rwanda
Can it spread through plant parts ?
Can it spread via other plants ?
Is there a vector ?
If so, how good is it?
How important is plant vs. vector spread ?
What are the effects of environment ? (crop
intensity, crop management, variety, temperature)
Are all these things the same or different for
different viruses ?
New Understanding of EpidemiologyEpidemiology Questions
What are the conditions for doing
epidemiology experiments ?
Guaranteed CBSV-free planting material
TC introductions through NRI partnership
Establishment of isolated nuclear multiplication sites
Usambara Mountains – eastern Tanzania
Sensitive, reliable and robust diagnostics
Developed with IITA-Ibadan, NRI and FERA
Routine RT-PCR and real-time RT-PCR in Tanzania
Extensive experimental programme
Field and screenhouse experimental sites set up
Whitefly Control – CBSV Epidemiology
TC Epidemiology Trial – Kibaha,
Tanzania
TC Epidemiology Trial – Kibaha,
TanzaniaSecond Planting, cv. Kiroba – 4 sites
CBSD Epidemic Simulation - Kibaha
Materials: CBSD-infected spreader, CBSD-free test plants,
whiteflies introduced
Treatments: Drought and fertilization
Replicates: 1 (next to spreader) to 4 (far from spreader)
CBSD Epidemic Simulation Results
Inoculum Pressure Assessment StudyTertiary Multiplication Sites
Question? How does the location of a tertiary site
affect CBSD infection
Plan: Assess inoculum pressure for 20 tertiary
sites in Lake Zone, Tz
Measured: CBSD in multiplication sites as well as
surrounding farmers’ fields
Factors Compared: District, Source of planting
material, Inoculum pressure, Virus species
Virus Diagnostics: Used to confirm virus
presence and identity
CBSD incidence in multiplication sites vs.
surrounding farmers’ fields
Effect of distance from surrounding farmers’ fields
on CBSD incidence in multiplication sites
CBSVs in Inoculum
Pressure Study
(IITA-Tanzania)
21 CBSV 10-11
138 CBSV 10-11
120 CBSV 10-11
57 CBSV 10-11
108 CBSV 10-11
121 CBSV 10-11
116 CBSV 10-11
101 CBSV 10-11
94 CBSV 10-11
92 CBSV 10-11
141 CBSV 10-11
12 CBSV 10-11
135 CBSV 10-11
26 CBSV 10-11
80 CBSV 10-11
102 CBSV 10-11
18 CBSV 10-11
106 CBSV 10-11
131 CBSV 10-11
145 CBSV 10-11
137 CBSV 10-11
AY008440 short
AY008442 short
AY008441 short
AF311052 short
AF311053 short
141 CBSV UG
142 CBSV UG
123 CBSV UG
CBSV MLB9 short
129 CBSV UG
96 CBSV UG
54 CBSV UG
62 CBSV UG
DQ837303 short
DQ837302 short
DQ837304 short
22 CBSV UG
72 CBSV UG
98 CBSV UG
121 CBSV UG
105 CBSV UG
122 CBSV UG
35 CBSV UG
25 CBSV UG
25 CBSV 10-11
35 CBSV 10-11
98 CBSV 10-11
72 CBSV 10-11
52 CBSV 10-11
93 CBSV 10-11
CVYV short
25
65
65
37
45
90
37
18
14
48
50
19
49
10
57
72
43
75
36
98
65
32
62
30
50
43
0.02
CBSV
UCBSV
Farmers’ Fields:
Both UCBSV and CBSV
Tertiary Sites:
Mainly CBSV
Inoculum Pressure Assessment StudyOutcomes
Key Factors in CBSD infection?
Source of planting material: No
District location: No
Virus species prevalent: No
Proximity to neighbouring fields: YES
QMP outcomes: 8 out of 22 fields failed. All
isolated fields passed
Control implications: Isolation critical.
Training required
Vector TransmissionIITA partnering with NRI, UK (Maruthi)
CBSV/UCBSV: Summary of NRI/IITA PhD
results
Irrefutable confirmation of B. tabaci as vector
Min. acquisition period – 5 mins
Min. Inoculation period – 30 mins
Max. retention time – 1 hour
Results suggest semi-persistent transmission
Regional EpidemiologyTanzania Lake Zone Surveys 2000-2009
(Jeremiah and Ndyetabula)
Wf Pk 1 Wf Pk 2 Wf Pk 3 CBSD>10 CMD >50
Bukoba 2000 2004 2007 2008 2000
Muleba 2000 2004 2007 2007 2001
Biharamulo 2000 2004 2007 2007 2001
Karagwe 2002 2004 2009 2008 2005
Ngara 2002 2007 2009 2008 2005
Ukerewe 2000 2002 2009 2007 2001
Geita 2002 2009 2008 2001
Sengerema 2004 2009 2008 2005
Mwanza 2004 2009 2009 2003
Magu 2004 0 2009 2005
Kwimba 0 0 0 2007
Misungwi 2004 0 0 2007
Kibondo 2004 2007 0 2003
Kasulu 2004 2007 2008 2003
Kigoma 2004 2007 2009 0 2007
Bukombe 2004 2007 2009 2008 2005
Kahama 0 0 0 2009 0
Bunda 2004 2007 2007 2007
Musoma 2004 2007 2009 2007 2005
Tarime 2004 2007 2009 2007 2005
Serengeti 2007 2009 2008 2005
Whitefly Population Peaks vs.
Disease Outbreaks
0
2
4
6
8
10
12
W h it e ly a b u n d a n c e p e a k s
A v e r a g e D if f e r e n c e in Y e a r s
Proposed Model for Epidemiology
of CMD and CBSD Pandemics
Monster Taming StrategiesThe Case of CBSD
Taming Strategy Also Called Who Wins?
1 (Murder) Eradication Humans
2 (Infection) Mitigation Mainly humans
3 (Friendship) Co-existence Mainly monsters
4 (Chasing) Chasing Monsters Humans
Monster Taming StrategiesThe Case of CBSD
Taming Strategy Also Called Who Wins?
1 (Murder) Eradication Humans
2 (Infection) Mitigation Mainly humans
3 (Friendship) Co-existence Mainly monsters
4 (Chasing) Chasing Monsters Humans
Resistance breeding for CBSV
Tolerance and resistance. Continue
existing search
Wild relatives. Identify new sources of
resistance
Biotech approaches. Molecular markers
and GM
Resistance breeding for whiteflies
Existing germplasm
Strengthen Mitigation
Application to Introduce Eretmocerus
hayati for the control of Bemisia whiteflies in
Tanzania
Presented at the 16th Biological Control Agents sub-Committee
(BCAS) Meeting
SRI, Kibaha – February 25, 2011
Strategic Laboratory Network
Virus testing and indexing. Standard
protocols
NARS facilities. Regional support from IITA
Virus-free propagation material. In TC
Virus-free Strategic Propagation Sites
‘Holding site’, ‘Clean seed site’
Regional sites for decentralized
propagation
Virus-free Cassava Seed Systems
Community PhytosanitationCollective Action to Eradicate Viruses
Primary
Recipient
Community
Secondary
Recipient
Community
> 200m