BACTERIAL WILT OF POTATO IN SUB-SAHARAN AFRICA NEW PERSPECTIVES ON AN OLD DISEASE

Kalpana Sharma1, M.L. Parker1, B. Ochieng1, A. Abdurahman1, J. Kreuze2, G. Nugundo3, E. Schulte-Geldermann1

1International Potato Center (CIP), Sub-Saharan Africa, Nairobi-Kenya2International Potato Center (CIP), Lima-Peru3Kenya Plant health inspectorate Service (KEPHIS), Nairobi-Kenya

WPC | ALAP | CUSCO, PERU | 2018

WPC | ALAP | CUSCO, PERU | 2018

Ralstonia solanacearum on Potato in SSA

➢ Notoriously destructive

pathogen

➢ Numerous economical crops

important in tropics: potato,

tomato, capsicum, tobacco,

eggplant

➢ Widespread, essentially

endemic in SSA

➢ Avoidance/quarantine

impossible in many regions

➢ Thus needs to be managed

WPC | ALAP | CUSCO, PERU | 2018

Potato Value Chain – Bacterial Wilt – Yield Losses

Y = -2.5281x + 26.97

R2 = 0.56

0

5

10

15

20

25

30

35

0 2 4 6 8 10

Bacterial wilt incedence (Sq root)

Ma

rke

tab

le y

ield

(t

ha-1

)

(P<0.001)

COUNTRY % loss

Burundi 30 – 70

Ethiopia 45-60

Kenya 50 – 70

Uganda 26 -100

D C

BA

Bacterial wilt present at all stages of potato value chain

Farmers predominately use poor quality seed, & consequently, low

yields in SSA (8-12 t/ha)

Ralstonia is a major cause of poor seed quality

WPC | ALAP | CUSCO, PERU | 2018

Bacterial Wilt, an Increasing Threat

• Low seed renewal frequency

• Lack of seed quality control systems

COUNTRY BW prevalence

Ethiopia 158 out of 263 farms

Kenya 128 out of 176 farms

Uganda 166 out of 288 farms

Alt

itu

de

(m)

Bacterial wilt reported year

• Detection of Ralstonia at >3000 masl

• Climate change in the favor of Ralstonia adaption

Go

Surv

ival

Pro

po

rtio

n

Year

Gondar

WPC | ALAP | CUSCO, PERU | 2018

144 bp: Phylotype I

372 bp: Phylotype II

280 bp: RS species complex

91 bp: Phylotype III

East Africa P I P IIA P IIB P III

Ethiopia x xKenya x x xUganda x x xRwanda On going

Bacterial Wilt, an Increasing Threat

Molecular genotyping of Ralstonia from Eastern Africa

➢ Molecular epidemiological studies are underway to understand the movement of Ralstonia within East African region

➢ Evidence based findings for policy makers, cross border seed movement

➢ Integrated seed health strategy

VNTR study of Ralstonia to trace bacterial wilt epidemic in Chencha, Ethiopia

WPC | ALAP | CUSCO, PERU | 2018

Seed Source on Bacterial Wilt

Strategy % bacterial wiltShangi

100% CF 0

100% PS 4 ± 7

100% RSFS 74 ± 24

20% CF + 80% PS 0

20% CF + 80% RSFS 5.3 ± 7.6

5% SSPT + PS 4 ± 6.9

5% SSPT + RSFS 1 ± 2.3

On-farm trial in Kenya

Three seasons, 8 farms (each a replication)

2014-2015

CF = certified seed

PS = positive selection seed

RSFS = randomly selected farmers seed

SSPT = small seed plot technique

WPC | ALAP | CUSCO, PERU | 2018

Soil Amendments

On-station, fully replicated trial, 2 seasons- 2014 and 2015

TreatmentMarketable yield

(t/ha)BW Incidence

(%)

10³ 10⁷ 10³ 10⁷

Neem cake @ 1 t/ha 33.7 19.6 20 33

Plantmate @ 1t/ha 33.1 21.4 13 35

Control 0 0 75 83

Neem cake @ 250 kg/ha 26.3 15.5 23 45

Neem cake @ 125 kg/ha 25.6 16.2 21 46

WPC | ALAP | CUSCO, PERU | 2018

Rotation Pattern and Best Rotation Crops

69

35

25

14

21

0

10

20

30

40

50

60

70

0 1 2

Number of break crops

Bacterial wilt incidence (%)

Marketable yield (t/ha)

>50%• Onion, spring onion, garlic– Peru, Ethiopia, Kenya• Brassica nigra – Ethiopia

25-50%• Cabbage, Canola

Pre -crops which reduced RS in soil and BW incidence

WPC | ALAP | CUSCO, PERU | 2018

INIA-Uruguay

CIP-Lima

CIP-EthiopiaEMBRAPA-

Brasil

Capturing resistance genes to bacterial wilt from S. commersonii into 4x cultivated genetic background

Race 3Bv2 Race 1

cmm phu2n=2x ; 2 EBN)

(cmm phu )

tbr

(2n=3x ; 2 EBN) (2n=4x ; 4 EBN)

(2n=5x ; 4 EBN)

BC1

BC2

F1

tbr

BC3

(2n=2x ; 1 EBN)

Procedures for Generation of Potato Tuber

Families from true (botanical) seed

Protocol for bacterial wilt resistance implementing a test

sensitive method for detection of R. solanacearum in

latently-infected tubers

WPC | ALAP | CUSCO, PERU | 2018

Bacterial Wilt Diagnostics

NCM-ELISA is the

standard test in seed certification

POCKET TEST Kit

Lateral flow device (LFD)

ImmunoStrip®

LAMP assay

How: Rapid detection of specific DNA or RNA targets; highly sensitive, target specific

Users: Public and private seed certification authorities as well as seed producers

2.2

×1

08

2.2

×1

07

2.2

×1

06

2.2

×1

05

2.2

×1

04

2.2

×1

03

2.2

×1

02

2.2

×1

01

CONVENTIONAL/ MULTIPLEX PCR

WPC | ALAP | CUSCO, PERU | 2018

Concluding Remarks

Holistic approach required in BW management combining improvements in:

➢ Disease management with suppressive soil amendments/ better rotations

➢ Host-plant resistant

➢ Disease free seed production and make it accessible to famers

➢ Improved diagnostics

➢ Positive seed selection for farm saved seed

➢ Integrated seed health strategy

THANK YOUEthiopian Institute of Agricultural

Research (EIAR)