Maize Lethal Necrosis
Disease:
Identification and
characterisation of causal
agents
Julian Smith
Noah Phiri
Symptoms
Identification at Fera in the UK
 Received samples of first
‘outbreak sites’ in Kenya
via CABI in early 2011
 ‘Traditional’ identification
methods proved
inconclusive
 Realised the significance
of the situation and need
for an answer
Next generations sequencing
(NGS) for identification of
unknowns
 Good at identifying what
is known and familiar
 Challenged when faced
with a new problem
 NGS was used to seek
out all virus, bacterial,
fungal nucleic acid
sequences in infected
samples
Quantification and assignment
of nucleic acid ‘signatures’ to
organisms
Probable causal agents
 Maize Chloritic Mottle
Virus (MCMV) and
Sugarcane Mosaic Virus
(SCMV) were shown to
account for the vast
majority of viral nucleic
acid
 MCMV and a potyvirus
associated with Maize
Lethal Necrotic Disease
 No other organisms
seemed to fit a ‘probable
cause’ hypothesis
Confirmation of association of
MCMV and SMV
 Real-time PCR assays
developed and tested on
individual samples
 MCMV identified with all
samples
 SCMV identified with some
samples only
 Plant test gave symptoms on
maize and barley for MCMV only
Inoculation of MCMV on Maize
Inoculation of MCMV on Barley
Nucleic acid alignment with
Genbank accessions
 MCMV had absolute similarity to a accession
described in China, and was with minor
separation from US accessions
 SCMV had a strong similarity to accessions of
Asian origin, that were characteristic of the
region and quite distinct from other SCMV
accessions sequence of other regions
Identification of MCMV in
Rwanda
 Samples received via CABI in 2013
 7 samples looked at and MCMV has been found in all, but
no SCMV or potyvirus has been found
 Characterisation shows these strains to be 100% identical
to Kenyan strains
 Awaiting further test data for any potyvirus associated with
samples
Identification with farmers – the
example of Plantwise
 Plantwise is a CABI product that
gathers and assimilates data on
plant pests for support to
research, policy and the private
sector
 Plantwise consists of two main
elements
− Knowledge bank
− Plant Health Clinics
Grass roots knowledge from
Plant Clinics
Plant Health Rally in DR Congo.
A farmer discusses what she
sees on cassava with a plant
doctor. Follow-up identified first
country report of CBSD
 Plant Clinics provide extension
services, modelled on a doctors
surgery
 The two-way flow of information
is gathered and assimilated
 A variation on Plant Clinics has
been successfully employed to
focus on priority pests
 Termed Plant Health Rallies,
these events provide tailored
information on a specific pests
such as MLND
MLND Plant Health Rallies in
Kenya for determining
distribution and giving advice
Map of Plant Health Rally
locations held in Kenya, 2013
 Events held in public
gatherings
 A fact sheet on MLND
symptoms was produced
and shared with farmers
 Many events held in a
short space of time
reaching many 100s of
farmers
 Information gathered on
distribution of MLND
Some key questions – amongst
many
Syngenta and Syngenta
Foundation staff review efficacy
of trials to control MLND, 2012
 Is MCMV the primary causal agent;
what role, if any, is with the potyvirus
 What are contributions of insect
vectors, alternate hosts and seed in
local and disparate spread?
 How do we map distribution and
achieve early outbreak notice
 Can visual field inspection be
sufficient for certification?
 What IPM packages for farmers and
industry?
 What are the roles of government
and industry in control?
Thank you
Staff of KEPHIS,
KARI and Pannar
Seed working at
Fera on developing
the diagnostics and
methods for MLND
detection