Plant Disease threats for 2009 Wheat viruses Stem rust Dr. Mary Burrows Montana State University, Bozeman, MT

WSMV: The Pathogen Family Potyviridae, genus Tritimovirus Mite-transmitted virus

Wheat streak mosaic virus Infects both winter and spring wheat –Symptoms in spring Earlier infection = greater yield loss Grassy weeds, volunteer wheat, corn, etc. can harbor both WSMV and the mite vector 5-10% yield loss/yr across Great Plains 100% yield loss in individual fields SDSU Extension

No chemical controls are effective for control of mite or virus

The life cycle of mite-transmitted wheat viruses

Weed Host: Volunteer Wheat

WSMV in Montana weeds Volunteer wheat is the best non-crop host, but weed species are also are infected with virus and may serve as a source

Which weeds are susceptible? Common nameLiterature 1 ELISA 2 Jointed goatgrassYesLocal Wild oatYes+ Downy BromeYesLocal Crested WheatgrassNo- Thickspike Wheatgrass No- QuackgrassNo+ Slender WheatgrassNo- Smooth BromeNo- BarnyardgrassYes+ Green FoxtailYes- 1 WSMV host data taken from Somsen 1970, Townsend 1996, and Brey, Data from MSU: 'Local' = Virus restricted to inoculated leaves in preliminary assay

Regional variation in the susceptibility of weeds to WSMV

Increase in regional virus incidence? Host PathogenEnvironment （ New York Times) SDSU Extension Vector

Determine prevalence of wheat viruses in the Great Plains (WSMV, HPV, TriMV, BYDV-PAV and CYDV-RPV)Determine prevalence of wheat viruses in the Great Plains (WSMV, HPV, TriMV, BYDV-PAV and CYDV-RPV) Nine states:Nine states: WY, MT, CO, KS, OK, TX, SD, ND, NE Determine geographic distribution for TriMV & HPVDetermine geographic distribution for TriMV & HPV Determine if host symptoms are diagnostic among virus species for single and multiple infectionsDetermine if host symptoms are diagnostic among virus species for single and multiple infections Collect and provide virus infected plant tissues to support research effortsCollect and provide virus infected plant tissues to support research efforts Increase communication about wheat viruses in the Great Plains RegionIncrease communication about wheat viruses in the Great Plains Region Wheat virus survey, 2008: Objectives

WSMV Range:28 – 83 Range:28 – 83 Mean:47 Mean:47 % samples infected 61 83

HPV Range: Range: Mean:19 Mean:19 % samples infected

TriMV Range: Range: Mean:17 Mean:17 % samples infected

mixed 37 WSMV +HPV WSM+ TriMV HPV+TriMV

Objective: Objective: Determine prevalence of wheat viruses WSMV detected in all GPDN states at high percentage infection (27 – 83 %)WSMV detected in all GPDN states at high percentage infection (27 – 83 %) HPV detected in all GPDN statesHPV detected in all GPDN states HPV identified in MT and WY for the first timeHPV identified in MT and WY for the first time TriMV identified in CO, KS, NE, OK, SD, TX, WYTriMV identified in CO, KS, NE, OK, SD, TX, WY TriMV not detected in MT and NDTriMV not detected in MT and ND

Race Evolution in TTKS (Ug99) Lineage & Implications to Resistance Breeding Yue Jin, USDA-ARS

Ug99 First reported in Uganda in Pretorius et al Plant Dis 84:203  Virulent on Sr31 Sr31 is located on 1BL.1RS translocation. Also carries Lr26, Yr9. Increased adaptation and higher yield. As a result, widely spread in wheat worldwide. Helped to reduce stem rust population worldwide.  Virulence to Yr9, originated in the eastern Africa in mid 80s, caused worldwide epidemics.

TTKS In 2002 and 2004, CIMMYT nursery planted in Njoro, Kenya were severely infected by stem rust. In 2005, we identified Kenyan isolates from 2004 were race TTKS. --Wanyera, Kinyua, Jin, Singh 2006 Plant Dis 90:113

Broad virulence of TTKS to North American spring wheat  US spring wheat CVs of the Northern Great Plains, known to have broad-based resistance to stem rust, were mostly susceptible (84%).  500 CIMMYT CVs released since 1950’s, 84% were susceptible. Conclusion: Ug99 possesses a unique virulence combination that renders many resistance genes ineffective. Jin & Singh, 2006, Plant Dis:90:

Projected potential pathways for Ug99 based on the migration of Yr9 virulence Singh et al CAB Review 1, 54

Ug99 migration Singh et al Advances in Agronomy v ? ?

Evolution of the TTKS lineage TTKSK TTTSKTTKST Sr24- Sr31+ Sr36- Sr24+ Sr31+ Sr36- Sr24- Sr31+ Sr36+ Our data point to: Jin et al Plant Dis. 92: Jin et al Plant Dis. (in Press)

% of resistance to TypeEntryTTKSKTTKSTTTTSK (Ug99)Sr24vSr36v Hard red spring8921%12%21% Hard red winter41629%15%28% Soft red winter37727%25%11% Western wheat603%3%3% Total94226%18%19% Ramification of Sr24/Sr36 virulence to US Wheat based on testing of 2007 elite breeding germplasm

The good news Phil and Luther are both working on it already! Li Huang, PSPP, is starting to map genes for resistance Fungicide trials with great results Communication and education ramping up!

Wheat stem rust fungicide trial results (2008) Stein and Gupta, SDSU Stem rust (% leaf area)

Triazoles Triazole + Strobilurin

Fungicide modes of action: Triazoles FRAC group 3 DMI (demethylation) inhibitors; biosynthesis of sterols in fungal cell membrane; spore penetration and mycelial growth Provides days of protection Medium risk of resistance development Greater mobility in plant than strobilurin fungicides Most widely used class of fungicide in the world Control a wide array of fungal diseases Protective and curative effects (if applied early in disease development)

Fungicide movement in the plant From: Tenuta, A., D. Hershman, M. Draper and A. Dorrence Using foliar fungicides to manage soybean rust.. Land-Grant Universities Cooperating NCERA-208 and OMAF. Available online at state.edu/SoyRust/

20 July, 2009, Fort Ellis stem rust fungicide trial (14 d after fungicide application, 45 d after pathogen inoculation) Control Triazole Strobilurin

20 July, 2009, Fort Ellis stem rust fungicide trial (14 d after fungicide application, 45 d after pathogen inoculation) Control Strobilurin Triazole

28 July, 2009, Fort Ellis stem rust fungicide trial (22 d after fungicide application, 53 d after pathogen inoculation) Spreader rowTriazole + Strobilurin

Fungicide modes of action: Strobilurins FRAC group 11 QoI (quinone outside) inhibitors (respiration); spore germination, penetration, and mycelial growth Provides days of protection High risk of resistance development because it has a very specific mode of action (they block electron transfer at the site of quinol oxidation (the Qo site) in the cytochrome bc 1 complex, thus preventing ATP formation) Originally isolated from wood-rotting fungi Strobilurus tenacellus ‘Reduced-risk’ pesticide (pose less risk to human health than other chemical options at the time of registration by EPA) Control a wide array of fungal diseases Excellent preventative fungicides, but limited curative effects “Plant health benefit” independent of disease control?

Figure 1. Mobility of trifloxystrobin, an example of a QoI fungicide.

Preventing fungicide resistance Limit the number of applications of a single FRAC group per season Limit the number of consecutive applications of a single FRAC group Mix fungicides with different modes of action (FRAC groups) Use early in disease development

Acknowledgements Dai Ito, graduate student Yue Jin, UMN Jeff Stein, SDSU