DISTRIBUTION OF MAIZE LETHAL NECROSIS, ITS VECTORS AND HOST
PLANTS IN MAJOR MAIZE GROWING AREAS OF UGANDA
PhD proposed research in Uganda by
Mudde Barnabas
PhD 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)

• 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 10 th 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

• 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.

Fine chlorotic streaks
Dead heart symptoms
Complete necrosis

• 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

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

Methodology
Survey in
13 districts of Uganda
Maize
ELISA and
PCR
Objective 1
Alternate hosts
Species identification
Collection of potential vectors of MLN causing viruses
Species identification
ELISA and
PCR
Objective 2
ELISA and PCR and transmission
Objective 3
Conduct studies to determine efficiency of transmission of different species of confirmed vectors of MLN viruses
Objective 4

• 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

Methodology cont’d
• 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)

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).

• 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

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