Dr. Suresh presented on maize lethal necrosis (MLN), a devastating viral disease affecting maize in East Africa. MLN is caused by a combined infection of the maize chlorotic mottle virus and sugarcane mosaic virus. It was first reported in Kenya in 2011 and has since spread to several other East African countries. MLN causes symptoms including chlorosis, necrosis, and premature death of maize plants, resulting in yield losses between 50-100%. Effective management requires integrated strategies like using virus-free seed, rogueing infected plants, controlling vectors, and growing resistant varieties.

1. Dr. Suresh, L.M.
Maize Pathology Lead – Sub Saharan Africa
Integrated Disease Management technologies
and approaches in Changing world
Global Maize Program
International Training program on Plant Health Mananagement Technologies and Approaches ,
Septermber, 2017

2. Maize an important food crop in the
Region
2
Consumption per capita is 98kg in
Kenya ( FAO, 2014)

3. Introduction
• The disease has affected many farmers in the east
African region since causing yield loses between 50% -
100%.
• Kenya and Uganda have both registered MLN as a
threat to food security in their country reports.

4. History of MLN
• First report of viral co-infection (MCMV+MDMV) leading to MLN was reported in
Kansas and Nebraska (USA) in 1976 (Niblett). Disease was termed Corn Lethal
Necrosis (CLN)
• In the 1990s, co-infection of MCMV+MMV was reported to cause extensive
damage to temperate seed production in Hawai.
• First report of MLN in Africa made in 2011 in Kenya (Wangai et al, 2012).
Causal agents identified to be MCMV and SCMV by tissue blot immuno-
assay and PCR.

5. MLN is a viral disease caused by
combined infection of maize with
Maize Chlorotic Mottle Virus
(MCMV) and any of the
Potyviruses infecting cereals,
especially Sugarcane Mosaic
Virus (SCMV)
The disease was first reported
in Africa, particularly in Kenya
in Sept 2011, and since then
reported in Uganda, Tanzania,
Rwanda, D.R. Congo, and
Ethiopia.

6. MLN Disease Development
Vectors:
Presence of
aphids and
thrips
Environment:
Conditions
favoring
vectors and
disease
Susceptible
Germplasm
Virus: Either
individual or
compound

7. MCMVMCMV
Potyvirus
SCMV
MDMV
WSMV
MLNMLN
• Individual infection with mixture of viruses can also cause disease
• Typically, infection with one virus results in milder symptoms than MLN but
reaction depends on germplasm and viral strain.
Maize Lethal NecrosisMaize Lethal Necrosis

8. Why is the MLN devastating in EA?
• MCMV is new to the region
• Potentially new strains of SCMV/MDMV
• Widespread cultivation of susceptible germplasm
that has never been screened for MCMV
• Characterization of viral populations will reveal
identify of strains in the region.

9. Source: Aisja Frenken (FAO REOA)
Spread of Maize Lethal Necrosis (MLN) in eastern Africa
Kenya Nov 2011
Tanzania Aug 2012
Rwanda Mar 2013
Uganda Oct. 2012
S. Sudan Jan 2013
Ethiopia June 2014
DRC March 2014

16. Disease Symptoms
• Dying leaves, leading to premature plant death
• Failure to tassel and sterility in male plants
• Malformed or no ears
• Rotting cob

17. Symptoms of the disease
• Symptoms observed vary widely depending on;
-Germplasm
-Time of infection
-Prevailing environmental conditions
-Ratios of the viruses infecting the plant
• The symptoms can easily be confused with drought ,
micro- nutrient deficiency or stalk borer infestation

18. Symptoms in artificially inoculated maize plants in
screen house
MCMV SCMV

19. Early Symptoms
Mild mosaic and mottling Mild mosaic and mottling

20. Chlorosis and Mottling Diffuse mottling and chlorosis
Early MLN Symptoms

21. Severe chlorosis and leaf necrosis

22. Shortened internodes and severe chlorotic mottle

23. ‘Dead Heart’ symptoms

24. Premature drying of the husks

25. Poor or no grain filling

26. 26
VIRULANT PATHOGEN
SUSCEPTIBLE
HOST
CONGENIAL
ENVIRONMENT
TIME
DISEASE

27. IPM
Integrated Pest Management

28. Management Strategies of Viral Diseases
Avoidance:
•Plant a location where the virus or vector is present
•Time planting so that plants are at a less susceptible growth stages when the virus and the vectors is present.
Avoidance:
•Plant a location where the virus or vector is present
•Time planting so that plants are at a less susceptible growth stages when the virus and the vectors is present.
Exclusion
•Impose quarantine ( local and international)
•Use virus free seeds
Exclusion
•Impose quarantine ( local and international)
•Use virus free seeds
Eradication:
Use herbicides to kill the weed hosts.
Rogue infected plants.
Use insecticides to kill vectors
Eradication:
Use herbicides to kill the weed hosts.
Rogue infected plants.
Use insecticides to kill vectors

29. Recommendation for prevention for disease spread

30. FARM TOOLS AND IMPLIMENTS
DISINFEACTION
A
V
O
ID
A
N
C
E
E
X
C
L
U
SI
O
N

31. E
R
A
DI
C
A
T
I
O
N
E
X
C
L
U
S
I
O
N

32. 32
SUCKING PESTS ROLE
Aphids
SuckingPests
Whitefly
Thrips
Transmits
Viruses

33. 33
Initial inoculum source
(Weed)
Vector – Transmits Virus
Rapid spread due to vector
movement and Host susceptibility Disease

34. Over-the-Top
Over-the-Top
Over-the-Top
Under
Dose
Optimum
Dose
Over
Dose
Under
Dose
Optimum
Dose
Over
Dose

35. Aerial View of MLN Screening Facility at Naivasha

36. MLN Screening Facility established by CIMMYT-KALRO at Naivasha, Kenya

37. MLN Phenotyping Service to Partners (2015-16)
Source of
germplasm
# of
germplasm
entries
# of rows
NARS in SSA 2568 5144
Private sector 3651 4390
Total 6,219 9,534
S.
No.
Institution
1 SeedCo
2 Western Seed
3 Pannar
4 Monsanto
5 Pioneer
6 NASECO
7 Syngenta
8 Tanseed
9 Gicheha Farm
10 Victoria Seed
Private Sector
Public Sector
S.
No.
Institution
1 KALRO-Kenya
2 EIAR-Ethiopia
3 ZARI-Zambia
4 RAB-Rwanda
5 KEPHIS
6 Makerere Univ.
7 NARS-South Sudan

38. First-generation MLN-tolerant hybrids released and being
scaled-up for delivery to farmers in eastern Africa
Country Variety Released
by
Seed
company
Uganda UH5354 NARO NASECO
Kenya H12ML KSC KSC
H13ML KSC KSC
Tanzania HB607 Meru-
Agro
Meru-Agro
5 more MLN-tolerant
hybrids recently
recommended for
release in Kenya.

39. 2nd
generation MLN Resistant Hybrids (Naivasha; 2016)
11 second-generation
CIMMYT-derived MLN
resistant hybrids presently
under NPTs in Kenya,
Tanzania and Uganda.

40. MLN Resistant Hybrids versus Susceptible Checks
Under high natural disease pressure in Tanzania
Yield advantage of at least 3-4
t/ha for MLN tolerant hybrids
(with a score of 1.0-2.0) under
high MLN pressure in farmers’
fields (in Tanzania), as compared
to MLN-susceptible commercial
checks (with a score of >3.5)
yielding 0 to <1.0 t/ha.

41. 1.Vehicles or machinery can introduce pathogens to production area from outside.
2.Vehicles can visit many places and agricultural area so wheels and car body can be contaminated by
pathogen
Precaution
1. Disinfect all vehicles and machinery before entering to our research /production area
2. If disinfection is not available, prepare parking lots isolated from
production area to prevent contamination. Red zone is allowed.
Risk:
Vehicle or agricultural machinery not disinfected

42. 1.All waste materials came from our GH/field area must be dumped at designated area only and
it should not throw away near facility or near walk way. Rain or people can carry pathogen and
this mechanism will cause disease again. If facility is poor without fence or less depth, plant sap
can overflow in rainy season and its sap can come to the field.
Precaution
1.Designate waste area far away from our field.
2.If it is not available, waste area will fenced and covered. Putting chemical or lime will stimulate
decomposing
2. Plant materials will bury or burn
Risk:
No waste designated area

43. MLN - infected MLN - free

44. Thank you
for your
interest!