2015 MAIZE DISEASE UPDATE

Wm. E. DolezalDuPont Fellow – Plant Pathology

Chicago, ILDecember 9, 2015

My Disclaimer

The thoughts and words in thispresentation 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 UpdateMaize 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 3Dr. 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.

Other MCMV hosts in Africa:• Sorghum• Sugarcane• Napier grass• Kikuyu grass

MCMV Host Range:

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:SystemicInfection

whichleads to

seed transmissionIn 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 seedtransmission 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 shotTropical Storm Bill & Tar Spot

Photo credit: Weather Underground

Current hypothesis:Long distance spore

movement viaTropical Storm Bill

Past Examples:• Sorghum Ergot• Asian Soybean Rust• Rpp9 Virulent Puccinia polysora

GEM Going Forward6.3- 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

Above photo credits: The American Phytopathological Society

Kernel Red Streak – a symptom of WCM feedingPotential Phytosanitary Implication

Potential Quarantine issues involving three vectored viruses• Wheat Streak Mosaic (a component of MLNV)• High Plains Wheat Mosaic Virus• Triticum Mosaic Virus

Suggestions: If you observed true kernel red streak on your corn kernels, have it tested.

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 towork with the GEM program for these

many years while at Pioneer.

GEM has been the model of public/privatecollaboration. I do wish you the very best

of success!

QUESTIONS?