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2015 MAIZE DISEASE UPDATE
Wm. E. Dolezal
DuPont Fellow – Plant Pathology
Chicago, IL
December 9, 2015
My Disclaimer
The thoughts and words in this
presentation reflect my views and my
personal opinion. They do not
necessarily reflect the views and opinions
of any company, trade or professional
association. They are derived from my
working nearly 35 years in the seed
industry in providing disease resistance
support to maize plant breeding
programs and in addressing
phytosanitary issues.
I will also try to express the valued input I
received from my friends and colleagues
in the public & private sectors who
shared their thoughts on this topic.
I will not try to repeat much of the same material that I presented last year.
I will focus this update on Maize Lethal Necrosis Virus
MLNV Update
Maize Lethal Necrosis Virus
Background Information:
MLNV is a complex involving two different viruses:
1. Maize Chlorotic Mottle Virus +
2. One of several “potyviruses”
• Sugarcane Mosaic Virus
• Wheat Streak Mosaic Virus
• Johnsongrass Mosaic Virus
Excellent article recently published:
July 2015 Phytopathology
FYI - Thursday @ 2pm in West Tower, Crystal Ballroom A, Grand Suite 3
Dr. Peg Redinbaugh is giving a presentation to the Phytosanitary Committee:
Maize Chlorotic Mottle Virus (MCMV) and Maize Lethal Necrosis (MLN) in Africa:
Status, Implications for U.S. Corn Seed Exports, Research Needs
Maize Chlorotic Mottle Virus Worldwide Movement Timeline:
Location
Year
Peru
1973
USA (KS,NE)
1976
Argentina
1982
Thailand
1982
Mexico
1989
USA (HI)
1992
Colombia
1999
China
2011
Kenya
2012
Rwanda
2013
Dem. Rep. Congo
2013
Taiwan
2014
Mechanically transmitted:
Multiple vectors for the virus
• Frankliniella occidentalis (HI)
• F. williamsi (Kenya)
@ 3 hr. acquisition feeding, thrips were
able to transmit . No latent period.
Larvae and adults are able to transmit
the virus for up to 6 days post acquisition.
MCMV Host Range:
Other MCMV hosts in Africa:
• Sorghum
• Sugarcane
• Napier grass
• Kikuyu grass
Other New MLNV Findings:
SCMV strains:
• Over 25 species of aphids transmit SCMV
• Two distinct SCMV Groups found in Kenya, one with common Asian origin
• Earlier diagnostic tools (ELISA) not able to detect some strains.
• Need diagnostic tools to rapidly and accurately identify virus
Seed Transmission Studies:
MCMV
• Historically – in USA, seed transmission ranged from 0.0% - 0.33%
• Kenya
• 18/25 (72%) detected by RT-PCR
• In pools of 10 seed bulked from local market 12/26 (46%) were positive
VIRUSES:
Systemic
Infection
which
leads to
seed
transmission
In developing
seed
vs.
Thrip feeding introduction of MCMV
into the kernels while on the ear.
“silk cut” is often thrip feeding injury.
Is this why there is a much higher seed
transmission rates in Africa vs. USA?
Other New MLNV Findings:
Soil Transmission:
Taken from G. Mahuku et al 2015. Maize lethal necrosis (MLN), an emerging
threat to maize-based food security in sub-Saharan Africa. Phytopathology
105:960.
Other New MLNV Findings:
Detection Methods:
• Some commercial MCMV & SCMV kits were not able to detect African strains.
• RT-PCR is much more sensitive and will detect high incidence vs. ELISA
• Detection does not necessarily translate to seedling infection.
• Some SCMV lack of detection due to wide variation in stains found.
Host Resistance:
• Resistance to Potyviruses known on Ch6 and Ch3
• Little is know of resistance to MCMV
• Some of J. Brubaker’s HI lines have shown some MCMV tolerance (HI)
• Genome Wide Association Studies (GWAS) & QTL mapping
• 9 SNPs associated with MLN
• 2 major QTLs on Ch3 (Bin 3.04/3.05)
• Major QTLs on Ch3 & Ch6, similar to that found for potyviruses
• ?? Coinfection with SCMV & MCMV leads to higher titer of MCMV
• Resistance to SCMV may lessen symptoms?
ISU-GEM USDA Allelic Diversity Doubled Haploid Releases
• Look for other chromosomal regions different than those
previously identified?
MLNV Proposal to ASTA
There is a real need to conduct extensive seed transmission studies!
“Be Prepared” – another warning shot
Tropical Storm Bill & Tar Spot
Current hypothesis:
Long distance spore
movement via
Tropical Storm Bill
Past Examples:
• Sorghum Ergot
• Asian Soybean Rust
• Rpp9 Virulent Puccinia polysora
Photo credit: Weather Underground
GEM Going Forward
6.3- Disease evaluation network: one item that was discussed by the
Development Team is the need to increase the disease evaluation network
using US and international Cooperators. Recently GEM has sent GEM coded
germplasm to be evaluated for MLN, a disease that has ruined the maize crop
in East Africa. This effort, and the recent good news about the work done by
our cooperators in Egypt who found several GEM germplasm lines to be
resistant to Late Wilt, are great examples of the unique opportunities that
GEM has to establish a more comprehensive disease evaluation network and
provide disease resistance information for diseases (or races of existing
diseases) that have not yet been introduced in the US. We suggest that the
new coordinator, with the help of the TSG, develop a plan to organize this
network to regularly obtain germplasm evaluation information on present
and possible future diseases. Some effort should be done also to develop a
more comprehensive database for Cooperators to access these informations.
More International Cooperation
Opportunities:
• Black Bundle vs. Late Wilt Disease
• Numerous Downy Mildews
• Viral Screenings
• Southern Corn Rust Race Determinations
Kernel Red Streak – a symptom of WCM feeding
Potential Phytosanitary Implication
Above photo credits: The American Phytopathological Society
Suggestions: If you observed true kernel red streak on your corn kernels, have it tested.
Potential Quarantine issues involving three vectored viruses
• Wheat Streak Mosaic (a component of MLNV)
• High Plains Wheat Mosaic Virus
• Triticum Mosaic Virus
Disease Update Summary
• MLNV & will continue to be important
– Ongoing research needed: Sources, diagnostic,
epidemiology – ASTA helping to fund basic research
– New viral phytosanitary barriers are going up which may
hamper GEM germplasm movement.
– GEM Going Forward opens opportunity to help to identify
new potential sources of disease resistance
• Investigate how to effectively use allelic diversity lines.
• GEM has great potential to help identify new sources
of resistance for seed industry
– Try to identify those offshore to have ready if needed.
It has been my great pleasure to
work with the GEM program for these
many years while at Pioneer.
GEM has been the model of public/private
collaboration. I do wish you the very best
of success!
QUESTIONS?