Maize Lethal Necrosis (MLN)
– What is happening in Africa
BM Prasanna and WL Trevisan
Infected maize fields in Bomet, Kenya (Sept
Disease Symptoms
What is Maize Lethal Necrosis (MLN)?
MCMV
Potyvirus
SCMV
MDMV
WSMV
MLN
Individual infection with MCMV alone can cause serious
disease (as seen in eastern Africa)!
Severe symptoms and yield loss (Rift valley, 2013)
Seed industry under stress in eastern Africa
Responses of some commercial maize hybrids against MLN
MLN in a Hybrid Seed Production Field in Tanzania
Losses due to MLN along the maize value chain
 Food and economic security at household and
national levels threatened
 Losses for seed producers (for both growers and
seed companies)
 Millers (both in quality and quantity)
 Transporters (reduced volume of business)
 Storage facilities (dormant capacity)
 Middlemen (loss of business volumes)
Why is MLN devastating in eastern Africa?
 New and perhaps highly virulent strains of
MCMV and SCMV
 Conducive environment for survival and spread
of insect vectors
 Continuous maize cropping in certain regions –>
build-up of virus inoculum
 Widespread cultivation of susceptible germplasm
that was never screened for MCMV
Distribution of MCMV and SCMV in 15 counties in Kenya2013
100
90
80
70
60
50
40
30
20
10
0
MCMV ONLY
SCMV ONLY
Sample size 3000
MCMV + SCMV
Source: Anne Wangai, KALRO
MLN Screening Facility established by CIMMYT-KALRO at Naivasha, Kenya
CIMMYT’s Rapid Response (several projects):
Intensive screening of maize germplasm (since 2012)
 Wide array of maize
germplasm screened
against MLN under
artificial inoculation
in MLN hotspots
during 2012-2014
 Promising MLN
tolerant inbred lines
and pre-commercial
maize hybrids
identified (although
<10% of total number
of germplasm entries
evaluated)
Summary of CIMMYT maize germplasm screened against MLN
under artificial inoculation (2012-2014)
Screening Completed
by
1st
Screening
Locations
Entries
Total Rows
Nov 2012
Olerai and
Naivasha
2636
5272
June 2013
Oleriai and
Marula farms
6021
16042
June 2014
Naivasha
15,712
32,807
Total
24,369
54,121
*
2nd
Screening
*
3rd
Screening
**
* CIMMYT, WEMA, DTMA, KALRO
** CIMMYT MLN Screening facility (ALL)
Identification of
MLN tolerant maize
germplasm
CLRCY039
(resistant)
CML395
(susceptible)
CML505
(susceptible)
CLRCY034
(resistant)
CIMMYT Update on MLN Tolerant Maize Germplasm
(May 2013)
CIMMYT Update on MLN Tolerant Maize Germplasm
(May 2014)
MLN Phenotyping Service initiated by CIMMYT to
Public and Private Sector Partners in Africa since 2013
S.No. Partner Institutions Total No. of Total No.
Entries
of Rows
1 WEMA/Monsanto
2000
4000
2 Monsanto, South
252
504
3 Pioneer
810
810
4 Western Seed,
1181
1861
5 EA Seed, Kenya
410
820
6 Seed Co, Kenya
540
540
7 NASECO, Uganda
156
156
8 Aminata, Tanzania
24
48
9 Zamseed, Zambia
221
487
5594
9226
Africa
Kenya
Total
MLN Marker Discovery and Validation by CIMMYT
Key Findings
 GWAS results from DTMA and IMAS AM panels
• Multiple leads – need to validate
• Favorable alleles from Mexico Lowland Tropical lines
 Three biparental populations evaluated against MLN
during 2012-2014
• Chr 6 potyvirus resistance locus detected in CML444 x
CML539
• Two large effect QTL identified on chr 3 from CML543
• One large effect QTL identified on chr 9 from CML494
 Full-sib genomic prediction from 0.58 to 0.66 based on
5-fold cross-validation
Understanding MLN Insect-vector Dynamics
 Survey and identification of vectors endemic
to eastern Africa that are capable of
transmitting MLN-causing viruses, especially
MCMV and SCMV
Aphids
 Determining patterns of insect-vector
movement and MLN disease development
under natural conditions.
 Understanding of the effects of novel seed
treatment technologies on the biology of
insect-vectors transmitting MLN-causing
viruses, and virus transmission competence.
A project being implemented by ICIPE since
2013 under CRP MAIZE to probe MLN insectvector dynamics in eastern Africa
Thrips
Leaf hoppers
Regional organizations in Africa are now
increasingly engaged on MLN
ASARECA-organized Workshop on
MLN (August 21-23, 2013) for
developing a regional strategy.
The workshop focused on:
1. reviewing the current efforts to
address the disease and identify
gaps
2. identifying priority areas that
need to be addressed that can
further be developed into a
proposal
3. developing a strategy and action
plan to address MLN in ECA
CIMMYT’s MLN-free Maize Germplasm Exchange Strategy
Three levels of phytosanitary regulation
Strict adherence to MLN management protocol at ALL
nurseries /seed production fields in MLN endemic
countries + official field inspection process
CIMMYT-internal testing for detection of MLN causing
viruses + official seed testing requirements, for safe
exchange of germplasm
CIMMYT’s MLN Quarantine Sites at Zimbabwe (from 2015)
for effective exchange of CIMMYT germplasm with
partners in Southern Africa
What we do not know yet
• How much is the extent of MCMV resistance in maize germplasm?
• What is the extent of MCMV/SCMV variability?
• What is the extent of seed transmission contributing to
introduction / spread of the disease? What are the possible factors
influencing seed transmission of MCMV?
• What are the alternative hosts (reservoirs) for MCMV/SCMV in
Africa?
• What is the role of MSV and other pathogens/stresses on MLN
epidemic?
• What is the role of insect-vectors (maize thrips, beetles, other
insects/nematodes) on MLN outbreak?
Thanks to…
 CIMMYT–Africa colleagues
 KALRO colleagues, NARS and
seed company partners across
Africa
 USDA/OSU and University of
Minnesota (especially Peg
Redinbaugh and Ben Lockhart)
 Donor agencies: Bill & Melinda
Gates Foundation, Syngenta
Foundation, USAID and CRP
MAIZE