Plant Disease threats for 2009Wheat viruses

Stem rust

Dr. Mary BurrowsMontana 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

Table 2. Capacity of prevalent grassy weeds in Montana to serve as mite and virus hosts.*Common name Scientific name Life cycle Mite host WSMV hostJointed goatgrass Aegilops cylindricae Annual Yes YesCrested wheatgrass Agropyron cristatum Perennial Unknown UnknownWild oat Avena fatua Annual No YesSmooth brome Bromus inermis Perennial Yes NoJapanese brome Bromus japonicus Perennial No UnknownDowny brome/Cheatgrass Bromus tectorum Annual Yes YesPersian darnell Lolium persicum Annual Unknown UnknownWestern wheatgrass Pascopyrum smithii Perennial Yes NoFeral rye Secale cereale Annual Unknown UnknownYellow foxtail Setaria glauca Annual No NoGreen foxtail Setaria viridis Annual Yes Yes*data taken from literature cited in text

Weed Host: Volunteer Wheat

WSMV in Montana weeds

Plant Ft.Benton Conrad site 1 Conrad site 2Wheat (in crop field) 68/100 42/100 66/ 100Crested wheatgrass 0/25 0/25 0/25Downy Brome N/ A 6/100 0/25Foxtail 0/25 0/25 0/25Wild oat 0/25 0/50 1/25Volunteer wheat 4/50 7/50

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?Which weeds are susceptible?

Common nameLiteratur

e1 ELISA2

Jointed goatgrass Yes LocalWild oat Yes +Downy Brome Yes LocalCrested Wheatgrass

No -

Thickspike Wheatgrass No -Quackgrass No +Slender Wheatgrass

No -

Smooth Brome No -Barnyardgrass Yes +Green Foxtail Yes -1WSMV host data taken from Somsen 1970, Townsend 1996, and Brey, 1998.2Data 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

Pathogen Environment（ New York Times)

SDSU Extension

Vector

• Determine prevalence of wheat viruses in the Great Determine prevalence of wheat viruses in the Great Plains (Plains (WSMV, HPV, TriMV, BYDV-PAV and CYDV-WSMV, HPV, TriMV, BYDV-PAV and CYDV-RPVRPV))

• 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 Determine if host symptoms are diagnostic among virus species for single and multiple infectionsspecies for single and multiple infections

• Collect and provide virus infected plant tissues to support Collect and provide virus infected plant tissues to support research effortsresearch efforts

• Increase communication about wheat viruses in the Great Increase communication about wheat viruses in the Great Plains RegionPlains Region

Wheat virus survey, 2008: Objectives

WSMVWSMV 4433

3388

4400

2288

3399

6622

2277

Range:Range: 28 – 28 – 8383

Mean:Mean: 4747

% samples infected

6611

8833

HPVHPV99

1199

1122

77

88

Range:Range: 7 - 417 - 41

Mean:Mean: 1919

% samples infected

1100

4411

3388

3300

TriMVTriMV00

2244

00

22

66Range:Range: 0 - 570 - 57

Mean:Mean: 1717

% samples infected

2277

3300

1100

5577

mixedmixed % samples infected

3377

WSMWSMV+HPV+HP

VVWSMWSM+ +

TriMVTriMVHPV+HPV+TriMVTriMV

99

88 1155

88

77

99

55

1166

0000

00

00

2211118855

2211113344

3355332288

8800

11001100

ObjectiveObjective: : Determine prevalence of wheat viruses

• WSMV detected in all GPDN states at WSMV detected in all GPDN states at high percentage infection (27 – 83 %)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 HPV identified in MT and WY for the first

timetime• TriMV identified in CO, KS, NE, OK, SD, TriMV identified in CO, KS, NE, OK, SD,

TX, WYTX, WY• TriMV not detected in MT and NDTriMV not detected in MT and ND

Yield of spring wheat varieties inoculated with WSMV

0

5

10

15

20

25

30

35

Reede

r

Chote

au

Mcn

eal

Conan

Fortu

na

Ernes

t

Corbin

Hank

Amido

n

Schola

r

Yie

ld (

bu

/a)

Not inoculated

Inoculated

Race Evolution in TTKS (Ug99) Lineage

&

Implications to Resistance Breeding

Yue Jin, USDA-ARS

Ug99

First reported in Uganda in 1999 --Pretorius et al. 2000 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:90:476-480

Projected potential pathways for Ug99 based on the migration of Yr9 virulence

Singh et al. 2006. CAB Review 1, 54

Ug99 migration

Singh et al. 2008. Advances in Agronomy v981998 2001?

2004

2003?2005

2006

2006

2007

Evolution of the TTKS lineage

TTKSK

TTTSKTTKST

Sr24-Sr31+Sr36-

Sr24+Sr31+Sr36-

Sr24-Sr31+Sr36+

Our data point to:

Jin et al. 2008. Plant Dis. 92:923-926Jin et al. 2009. Plant Dis. (in Press)

% of resistance to

Type Entry TTKSK TTKST TTTSK(Ug99) Sr24v Sr36v

Hard red spring 89 21% 12% 21%

Hard red winter 416 29% 15% 28%

Soft red winter 377 27% 25% 11%

Western wheat 60 3% 3% 3%

Total 942 26% 18% 19%

Ramification of Sr24/Sr36 virulence to US Wheatbased 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

Ste

m r

ust (

% le

af a

rea)

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 14-21 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. 2007. Using foliar fungicides to manage soybean rust.. Land-Grant Universities Cooperating NCERA-208 and OMAF. Available online at http://www.oardc.ohio-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 row Triazole + Strobilurin

Fungicide modes of action: Strobilurins

• FRAC group 11• QoI (quinone outside) inhibitors (respiration); spore germination,

penetration, and mycelial growth• Provides 14-21 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 bc1 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. http://www.apsnet.org/education/AdvancedPlantPath/Topics/Strobilurin/top.htm

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 studentYue Jin, UMNJeff Stein, SDSU