maize lethal necrosis (mln): progress in finding solutions to a new threat to maize in africa

www.iita.org A member of CGIAR consortium

Maize Lethal Necrosis (MLN):

23 November 2015 (R4D Week 2015)

Progress in finding solutions to a new threat to maize in Africa Lava Kumar et al

A member of CGIAR consortium www.iita.org

23 November 2015, R4D Week 2015

Maize Lethal

Necrosis (MLN): Progress in finding solutions to a new threat to maize in Africa

Lava Kumar et al.

[email protected]


Viral disease of maize


Maize streak virus (MSV) is an

endemic threat to maize in Africa

Leaf hopper (C. mbila)

• Widespread in Africa

• Transmitted by leafhoppers

• Causes severe yield reduction in

susceptible lines

• MSV resistant lines developed for

disease control


Outbreak of a new maize

disease in Kenya

• First outbreak in

September 2011 in Bomet

county in Kenya

•Necrosis, rapid decline

and premature death of

plants

•Rapid spread within and

between the fields

•Referred as ‘Bomet

Disease’


Outbreak of a new maize disease



Cobs from MCMV infected plants



• Yield losses vary from 30 to 70% depending on the

stage of infection

• In 2012, MLN outbreak in Kenya affected 77,000 ha ;

destroyed production worth US$52 million

• All the farmer adopted lines and hybrids are highly

susceptible


Maize chlorotic mottle virus

Sugarcane mosaic virus

The new disease identified as maize lethal necrosis

(MLN) caused by mixed infection of two viruses


The new disease identified as maize lethal necrosis

(MLN) caused by mixed infection of two viruses

SCMV

+

MCMV

Synergistic

interaction

• SCMV is known to be endemic and widespread in Africa. Not known to

be a threat to maize.

• MCMV is a new record in the continent; and the main contributor for

MLN outbreak.

• MCMV on its own can cause severe symptoms and yield losses.

• Both viruses have wide host range


Pedigree

Grain Yield (tha-1)

Optimal Conditions

Grain Yield (tha-1)

MLN

SYN(B)F2-5-8/CML539/CML442 7.6 2

SYN(B)F2-17-1/CML539/CML442 7.2 2.2

SYN(B)F2-14-3/CML539/CML442 7.1 1.8

SYN(B)F2-17-4/CML539/CML442 7.1 2.2

SYN(B)F2-19-4/CML539/CML442 7.1 1.6

SYN(B)F2-11-11/CML539/CML442 7.1 2.2

SYN(B)F2-5-5/CML539/CML442 7.0 2.9

SYN(B)F2-23-5/CML539/CML442 7.0 2.1

SYN(B)F2-22-3/CML539/CML442 7.0 1.4

SYN(B)F2-5-1/CML539/CML442 7.0 1.5

SYN(B)F2-5-4/CML539/CML442 7.0 1.1

SYN(B)F2-14-13/CML539/CML442 7.0 1.3

SYN(B)F2-9-1/CML539/CML442 6.9 1.5

SYN(B)F2-6-6/CML539/CML442 6.9 2.5

SYN(B)F2-12-2/CML539/CML442 6.9 1.1

SYN(B)F2-12-3/CML539/CML442 6.9 1.3

SYN(B)F2-17-3/CML539/CML442 6.9 2

SYN(B)F2-14-14/CML539/CML442 6.8 1.7

SYN(B)F2-7-1/CML539/CML442 6.8 2.2

SYN(B)F2-7-3/CML539/CML442 6.8 1.7

SYN(B)F2-11-8/CML539/CML442 6.8 0.4

Commercial Check 6.0 0.9

Mean 6.4 1.60

LSD (0.05) 2.3 1.33*

CV 18.8 41.85

Maize yield losses associated

with MLN-Babati

75%

reduction in

yield


2004

Thailand

2010

China

2012

1974

Peru

1976

USA 1989

Mexico

MCMV distribution

MCMV has been identified in two MLN outbreaks

1. Kansas state USA (1980s)

2. Eastern Africa (since 2011)


Distribution in Africa

•Kenya (2012)

•Tanzania (2013)

•Uganda (2013)

•Rwanda (2013)

•Burundi (2013)

•South Sudan (2013)

•DRC (2014)

•Ethiopia (2014)

MCMV spread in Africa


• Delayed initial diagnosis

– Unfamiliar disease

– Lack of awareness

– Lack of diagnostic capacity

• Once established, difficult to control

• Limited control options (mainly regulatory control)

– Multiple sources of inoculum • Soil, residues and water

• Seed

• Vectors

Challenges to MLN control


IITA’s R4D focus on MLN

•MLN epidemiology (AfricaRISING and CRP): Causes and factors

contributing to disease spread

•Development of MLN diagnostics (BMGF, AfricaRISING and CRP):

Tools for reliable detection of causal viruses

•Breeding for MCMV resistance (CRP & BMGF): Evaluation of

maize lines for assessing host response to MLN causal agents and

finding promising lines for breeding

•Risk assessment & pre-emptive management (CRP): Determine

the spread risk potential and preparedness in Central and Western

Africa.

SARI

Sealian Agricultural

Research Institute


1. Understanding MLN Epidemiology

Sub-Humid District

(1610 to 2178 mts)

Semi-Arid Districts

(1261- 1527 mts) Medium elevation

Studies in Tanzania


MCMV + SCMV

(MLND)

MCMV only

MCMV SCMV

SCMV+

MCMV MSV

51 (64%) 18 (22.5) 17 (21.5) 16 (20)

Viruses detected (N = 80 samples)

SCMV only

Incidence of MLN agents differ

First survey in 2013

•MCMV alone can cause severe symptoms


MCMV spread into DRC

• Only MCMV was detected in the MLN

outbreak in DR Congo.

• It is very likely that MLN-like severe

symptoms can result from MCMV infection

alone.

• Controlling MCMV is critical for MLN control


MLN surveys in 2015 in

Tanzania

Widespread and expanding; incidence between 5 to 70%


0.0

20.0

40.0

60.0

80.0

100.0

120.0

1

4

7

10

13

16

19

22

25

28

31

34

37

40

43

46

49

52

55

58

61

64

67

70

73

76

79

82

85

88

91

94

97

100

103

106

109

112

115

118

121

124

127

Manyara Dodoma Arusha

Babati

Perc

ent in

cid

ence

Prevalence and incidence of maize lethal

necrosis in 2015 crop season (N = 116)

Kiteto Hanang Mbulu Simanjiro K Kongwa A Kondoa M Ch Mo


MLN Virus MSV

Incidence of viruses

1 - 34% 1 - 62% 0 - 37%


MLN Virus MSV

Prevalence of viruses

10 - 100% 51 - 100% 0 - 100%


JX286709-MCMV (Kenya)

MCMV-DRC (KJ699379)

JQ982468-MCMV (Yunnan2)

KF010583-MCMV (Yunnan)

GU138674-MCMV (Yunnan)

EU358605-MCMV (USA)

X14736-MCMV (USA)100

99

84

63

0.002

MCMV diversity in East Africa

•Viral isolates from Kenya, Tanzania and DRC

are 99 – 100% identical to MCMV China isolates

•SCMV isolates were similar but greater

diversity observed in some locations

Afr

ica


D02_Rm2COI_826285

E02_Rm3COI_826286

G04_RmECR1_826304

G11_RmECR2_826360

H11_RmECR3_826361

A05_RmAIbo_826306

B01_F11TTa_840483

D03_Rm4COI_826293

C02_Rm1COI_826284

F02_Rm3bCO_826287

HQ112195India-R maidis

F01_F12Tan_840487

G01_F9Tanz_840488

A01_F10Tan_840482

C01_F11BTa_840484

TANZF13COF

D01_F2Tanz_840485

GU457795RhoKorea-R padi

GU140277Canada-P nigronervosa

100

100

99

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.07

0.02

0.03

0.04

0.01

0.01

Rh

op

alo

sip

hu

m m

aid

is

Rh

op

alo

sip

hu

m p

ad

i

• Molecular analysis (COI gene-based taxonomy) confirmed R. padi

as common aphid vector of SCMV.

• Corn thrips, Frankliniella williamsi common vector of MCMV

MLN Vectors


Late planting in March

(High incidence)

Early planting in

January (no or low

incidence)

MLN disease cycle

Vectors

Maize growing period


MCMV Seed transmission

•Seed collected from infected plants for

seed transmission assay

•High rate of seed loss due to fungal

infection. Survived seed planted.

•Total 48 batches of 7 hybrids / lines; 500

seed tested per batch.

•11,527 of 24,000 planted seed germinated

(48% germination)

•No evidence of MCMV in the seed lots

tested

•MCMV seed transmission suspected for long range spread in Africa

•Previous reports indicated 0 to 0.33% rate of MCMV seed transmission

•MCMV can be detected in the seed


2. New diagnostics for MCMV

Scaling of new diagnostic tools developed in

AfricaRISING

•New diagnostics for MCMV

developed in 2013-14

•Recombinant polyclonal

antibodies against MCMV


• Single tuber Multiplex PCR for simultaneous

detection of all the major maize viruses

Improving diagnostics

10-1 -2 -3 -4 -5 -6 -7

Multiplex assay detected up to

10-3 dilution


New diagnostics

RT-

LAMP

Dilutions MCMV MSV

1 1:1000 + +

2 1:5000 + +

3 1:10000 + +

4 1:100000 + +

5 1:1000000 + +

6 1:10000000 + -

7 Buffer - -

8 Water - -

MSV

MCMV

• Reverse transcriptase/Loop-mediated isothermal amplification

(LMPA) assay.

• Further modified to develop UDG-LAMP to avoid contamination


• Established a MLN diagnostic Lab at Selian

Agricultural Research Institute (SARI), Arusha

• Pathology lab refurbished with essential equipment

• Training to staff

Developing diagnostic capacity


• 22 persons trained from Tanzania and

• Field and lab diagnosis | Insect vector identification

• Disease control

Developing diagnostic capacity


3. Breeding for MLN Resistance

• IITA initiated pre-emptive breeding for deploying MLN resistance

in cultivars and lines preferred in West and Central africa

• Evaluation CIMMY – KALRO MLN phenotyping facility at Naivasha,

Kenya


Initiation of pre-emptive breeding against the

spread of MLN to West and Central Africa

• 40 elite inbred lines screened and 3 promising inbred lines with

moderate resistance to MLN identified

• Used as partners to develop 22 bi-parental crosses in 2014

• The 22 bi-parental crosses were self pollinated in 2015 to

develop MLN resistant inbred lines

• Additional 33 bi-parental crosses involving other elite

inbred lines were successfully made in 2015

• Inbred lines with resistance to MLN introduced from CIMMYT

for crossing to expand the genetic base of resistance source

germplasm


0.0

1.0

2.0

3.0

4.0

5.0

6.0

Score1 Score2 Score3 Score4

ML

N S

co

res

(1

-5)

TZMI730 TZMI746

TZMI723 TZMI740

TZMI764 TZMI765

• Identification of MCMV resistant lines for use in crossing

Initiation of pre-emptive breeding against the

spread of MLN to West and Central Africa

TZMI723

TZMI730 TZMI746


•SCMV and MSV detected but not MCMV

•Aphids and thrips are widely distributed

• Baseline study for maize

viruses

• Assessment of risk to

seed production sector

• Awareness creation

about MLN

• Capacity development

of regulatory authority

• Understanding viruses

in perennial cereal

hosts (e.g. sugarcane)

Pre-emptive control


Unknown’s

•Rate of transmission

•Virus transmission through seed

•Inoculum survival

•Vector diversity and their role in spread

•Effect of environment and farmers practices

•Disease distribution in MLN affected countries

Knowledge gaps


MLN: Ebola of Maize

•MLN outbreak is a spoiler of maize revolution in Africa.

•Severely reduced maize production

•Crippled commercial seed industry in Kenya

•Forced re-strategising of maize improvement

programs (search for identification of high levels of

resistance to recovery maize production)

•Pre-emptive control (surveillance), preparedness and

emergency response plans are critical to save maize

from invasive threat.

Conclusions & Lessons


Acknowledgments

SARI

Sealian Agricultural

Research Institute

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maize lethal necrosis (mln): progress in finding solutions to a new threat to maize in africa

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