DISTRIBUTION OF MAIZE LETHAL NECROSIS, ITS VECTORS AND HOST PLANTS IN MAJOR MAIZE GROWING AREAS OF UGANDA

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DISTRIBUTION OF MAIZE LETHAL NECROSIS, ITS
VECTORS AND HOST PLANTS IN MAJOR MAIZE GROWING
AREAS OF UGANDA
PhD proposed research in Uganda by Mudde
BarnabasPhD student, University of Nairobi
Presented During The Workshop To Develop
Strategic Plan For Maize Lethal Necrosis Disease
For Eastern And Central Africa, Jacaranda Hotel,
Nairobi, Kenya 21st -23rd August,
2013 Supervisors 1. Prof . Olubayo Florence,
Faculty of Agriculture, University of Nairobi 2.
Dr. Miano Douglas, Faculty of Agriculture,
University of Nairobi
3. Dr. Asea
Godfrey, National Agricultural Research
Organisation (NARO)
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Background

• Maize Zea mays (L.) is one of the chief starchy
  cereal crops in East Africa
• It is the vital staple for over 70 million people
  
• Uganda ranked 10th in Africa
• Annual production estimate at 1,373,000 tonnes
• Annual yield is 1.5 tons per hectare
• Low yields majorly attributed to biotic
  constraints
• Major biotic constraints include diseases caused
  by
• Fungi
• Bacteria
• Viruses
• Most important viruses are
• Maize streak virus, Maize rough dwarf virus
• And the new Maize lethal necrosis

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Maize lethal necrosis disease

• Maize Lethal Necrosis disease (MLN) first
  identified in USA in 1976 In East Africa from
  Kenya and Tanzania (2011) In Uganda (2012).
• Symptoms include drying of leaves, premature
  plant death failure to tassel / sterility in
  male plants malformed /no ears premature drying
  or rotting of cobs
• Potential yield losses 30 -100 . (Wangai et al.,
  2012)
• MLN caused by double infection with Maize
  chlorotic mottle virus (MCMV) and any of cereal
  viruses in Potyviridae group Sugarcane mosaic
  virus (SCMV), Maize dwarf mosaic virus (MDMV) or
  Wheat streak mosaic virus (WSMV).
• MLN-causing viruses are transmitted by several
  insect vectors. MCMV (thrips and beetles) MDMV
  and SCMV (aphids).
• Alternate hosts of MLN causing viruses include
  Maize, sugarcane, grasses of family poaceae,
  sorghum, millet and johnson grass.

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Symptoms
Fine chlorotic streaks
Dead heart symptoms
Complete necrosis
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Problem statement

• Maize Lethal Necrosis disease (MLN) stands out as
  greatest threat to African food security crop
  (maize).
• In 2012, this MLN disease outbreak was first
  reported in Busia district in eastern Uganda, it
  is not known to what extent this disease is now
  prevalent and distributed in Uganda.
• It is not known which maize viruses of the
  Potyviridae group in Uganda could be combining
  with MCMV to cause the MLN symptoms observed in
  maize fields so far.
• Apart from maize, the maize lethal necrosis
  causing viruses are haboured by alternate plant
  hosts. The potential plant hosts for MLN causing
  viruses in Uganda not known.
• The vectors of the MLN-causing viruses in Uganda
  are not known and their virus transmission
  efficiency.
• Plant virus epidemics are multi-component systems
  resulting from interactions between the virus
  (es), vectors and host plant (s).
• A full understanding of the epidemiology of MLN
  disease is critical for development of
  sustainable management strategies

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Objectives

• General Objective
• To provide a better understanding of the
  epidemiology, host plants, vector range of MLN
  disease for improved control
• Specific objectives of the study
• 1. To establish the distribution and incidence
  of MLN in Uganda
• 2. To determine alternate hosts of MLN causing
  viruses in Uganda
• 3. To identify potential insect vectors of MLN
  causing viruses in Uganda
• 4. To determine transmission efficiencies of
  vectors of MLN causing viruses in Uganda

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Methodology
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Methodology

• Objective. 1 . Distribution, incidence and
  severity of MLN in major maize growing districts
  of Uganda
• Data from 13 major maize-growing districts of
  Uganda
• Disease incidence Estimate of percentage of
  maize plants infested
• Severity assessed using a 1 to 5 scale by
  Biswanath et al. 2013
• GPS coordinates recorded

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Methodology contd

• Activity 1.1. Serological and molecular detection
  of MLN in maize samples
• Lab studies at National Crop Resources Research
  Institute, Namulonge in Uganda.
• ELISA against MLN causing viruses (MCMV, SCMV,
  MDMV, WSMV) as well as antibodies against the
  entire Potyvirus genus (AGDIA, Elkhart,IN).
• Confirmation with reverse transcription-polymerase
  chain reaction (RT-PCR) using specific primers
  (Wangai et al., 2012)

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Methodology contd

• Objective 2 Identification of alternate plant
  hosts of MLN in Uganda
• Alternate MLN host plants collected from
  confirmed hotspots of MLN in Uganda.
• Identified to species level in collaboration with
  Botany and Zoology department of Makerere
  University Institute of Environment and Natural
  Resources
• ELISA against MLN causing viruses (MCMV, SCMV,
  MDMV, WSMV) as well as antibodies against the
  entire Potyvirus genus (AGDIA, Elkhart,IN).

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Methodology contd

• Objective 3 Identification of potential insect
  vectors in Uganda
• Activity 3.1. Vector collection
• Sampling vectors from confirmed hotspots of MLN
  in Uganda.
• Potential vectors colonizing maize will be
  identified to species level in collaboration with
  ICIPE.
• Insect vector viral content MLN causing viruses
  will be determined using Enzyme Linked
  Immunosorbent Assay as previously described by
  Chu and Francki, (1982).
• Real time PCR will be also be used to quantify
  viral load in potential vectors

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Methodology contd

• Objective 4 Determine transmission efficiencies
  of potential vectors in Uganda to transmit MLN
• Vectors transferred to MLN-infected 3 week old
  maize
• For each insect vector, 3 species selected for
  transmission studies
• MCMV symptoms noted in seedlings at 5, 10, 15,
  20, after feeding
• Viral content will be measured at each of these
  stages using ELISA
• Percent transmission rates based on number of
  infected plants out of total observed

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Expected budget and output

• Budget USD 90,000
• Outputs
• 1. Incidence and distribution of MLN in Uganda
  established.
• 2. Knowledge of alternative hosts and
  vectors of MLN causing viruses prevalent in
  Uganda
• 3. At least 4 scientific papers and PhD thesis
  published.

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Acknowledgements

• NARO
• Government of Uganda
• Development Partners
• University of Nairobi

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