Goss’s wilt: Get the facts! Alison Robertson Charlie Hurburgh Lisa Shepherd Charlie Block and Roger Elmore

Goss’s leaf blight disease progress 21 July 2 August 25 August 9 September

Q. Where was Goss’s wilt in Iowa in 2011?

Q. What symptoms occur with Goss’s wilt? Usually first seen on top leaves

Q. What symptoms occur with Goss’s wilt? May be seen in mid canopy

Q. What symptoms occur with Goss’s wilt? Greasy “Freckles” Wavy, margin

Q. What symptoms occur with Goss’s wilt? Saprophytic fungi “Freckles”

Q. Is there a kit to diagnose Goss’s wilt? Clavibacter michiganensis subsp michiganensis ImmunoStrip Test (Agdia®) Cost: 5 for $32.50 25 for $120 5-10 mins

Q. Is there a kit to diagnose Goss’s wilt? CAREFUL!!!!! False positives example: Purple leaf sheath; other saprophytic bacteria on corn. Extremely sensitive cross contamination between samples Purple leaf sheath

Q. Has a new race of Cmn evolved? Race: a subgroup or biotype within a species Usually distinguished from other races by virulence symptom expression or host range but not by morphology (D’ Arcy et al. 2001) ICM 2008

Q. Has a new race of Cmn evolved? Standardized soybean lines are used to identify races of P. sojae 1a 1b 1c 1k 2 3a 3b 3c 4 5 6 7 8 1d C ICM 2008

Q. Has a new race of Cmn evolved? Rpp9 resistance to Southern rust fungus Puccinia polysora Photo courtesy of B. Dolezal, Pioneer ICM 2008

Q. Has a new race of Cmn evolved? Ht1 resistance to Northern leaf blight fungus Helminthosporium turcicum Race 1 Race 0 Photos courtesy of B. Dolezal, Pioneer ICM 2008

Q. Has a new race of Cmn evolved? 131 strains of Cmn 1969 – 2009 origin ICM 2008

A: no correlation with strain, xxiorigin, history Two groups: A and B A: no correlation with strain, xxiorigin, history B: all strains collected after 1999 13/69 strains = <20% (Agrakova et al., 2011) ICM 2008

Goss’s disease cycle Symptoms Bacteria overwinter in infested crop residue and seed Infection Cmn bacteria ooze from residue; splash dispersed Epiphytic infection

Q. How long does Cmn survive in corn residue? Goss’s wilt bacterium survives for at least 10 xximonths in infested surface crop residue Survival is significantly reduced in buried residue Goss’s Disease Index 0” 4” 8” Leaves 80 Stalks 75 30 40 Cobs 63 5 Pure culture (Schuster, 1975)

Can Cmn survive longer?

Survival C. m. subsp. michiganensis on tomato Buried infested residue: ~7 months Surface infested residue: 2 years Gleason et al., 1991

What effect might corn stover removal have?

Percent corn residue and GLS disease severity de Zareno and Lipps, 1993 More residue = greater disease

What effect does manure have on survival of Cmn? Population of C.m. subsp. sepedonicus on potato decreased as other microbes in cattle manure slurry increased (Roozen and Vanvuurde 1991) Composts amended with cattle or poultry manure reduced C. m. subsp. michiganensis of tomato (tomato canker) by 79 to 100% Populations of C. m. subsp. michiganensis in composts declined to undetectable levels in 15 to 21 days (Yogev et al, 2009) Looking at potato tubers spreading ring rot of potato. Work done in Netherlands – no ring rot reported their. Pigs and cows eat tubers – if tubers are infected – could introduce.pathogen

Q. Was Goss’s wilt introduced on Cmn-infected seed? Seedborne infection (seed infection): pathogen carried on or in a seed Seed transmission: pathogen in or on seed infects developing seedlings Biddle et al, 1990

Q. Was Goss’s wilt introduced on Cmn-infected seed? Inoculated field trial Leaves of plants inoculated at V3, V6 and VT Seed infection: 17.1 - 30.7% Seed transmission: none detected (N=12000 seed) Biddle et al., 1990 Natural infection in field Seed naturally infected with Goss’s wilt Seed infection: 2 – 39% Seed transmission: 1 in 12864 seedlings. - single case found in 29% seed lot Shepherd, 1999 & 2011 Biddle et al, 1990

Q. Are there other hosts of Cmn? Several common weeds are secondary hosts of Cmn Green foxtail Shattercane Sudangrass Eastern gamagrass Schuster, 1975

Q. Are there other hosts of Cmn? Other susceptible hosts: sugarcane –atypical symptoms Resistant to infection: Oats Barley Wheat Bromegrass Orchardgrass Crabgrass Barnyard grass Proso millet Yellow foxtail Johnson grass Sugarbeet cabbage Chrysanthemum Poinsettia Tomato Petunia Potato Schuster, 1975

Q. Is there resistance to Cmn? Several genes quantitatively inherited not complete, i.e. no immunity known either leaf blight or wilt 115 bu/acre yield difference

Effect of Goss’s leaf blight on grain characteristics 9 fields 7 in Central IA; 2 in SW Iowa 8 hybrids from 3 major seed companies 2 to 11 locations per field Goss’s leaf blight severity at R3 or R5 Stalk rot severity prior to harvest 20 ears hand harvested per location

Goss’s leaf blight severity and stalk rot r=0.61 P=0.01 Robertson et al., 2011

Effect of Goss’s leaf blight on grain characteristics Variable <5% at R5 >5% at R5 P value # rows 16.4 (14.5-18.6) 16.9 (15.3-17.9) 0.175 # kernels per row 31.9 (29.2-34.6) 31.5 (29.7-32.6) 0.286 Seed weight (g/1000) 402.4 (327.8-472.0) 327.8 (245.2-395.6) 0.0001 Robertson et al., 2011

Effect of Goss’s leaf blight on grain characteristics Assessment <5% at R5 >5% at R5 P value Test Weight @ 15% moisture (lb/bu) 57.0 (55.2-60.3) 55.7 (53.6-60.6) 0.049 Starch (%) 60.8 (60.1-61.8) 61.3 (60.7-62.1) 0.041 Protein, oil and density: NS Robertson et al., 2011

Goss’s leaf blight severity and seed size r=-0.51 P=0.007 8 hybrids 8 hybrids Robertson et al., 2011

Goss’s leaf blight severity and seed size r=-0.77 P=0.001 2 hybrids These two hybrids are very closely related – one is RR and one is triple stack but they both have the same background genetics Robertson et al., 2011

Goss’s leaf blight severity and estimated yield loss 2 hybrids r=-0.87 P<0.001 Note – I also dropped the 100% severity from this – then r = 0.66 P=0.02 Robertson et al., 2011

Goss’s leaf blight severity and test weight 2 hybrids r = - 0.83 P=0.0002 Robertson et al., 2011

Seed Transmission (positive/ tested) Goss’s leaf blight severity and seed infection Goss's severity (%) Growth stage Seed Infection Seed Transmission (positive/ tested) 1 R3 5 R5 15 20 R5.25 35 R5.75 100 R5.5 ~R5

Seed Transmission (positive/ tested) Goss’s leaf blight severity and seed infection Goss's severity (%) Growth stage Seed Infection Seed Transmission (positive/ tested) 1 R3 0/200 5 R5 15 20 R5.25 35 R5.75 0/145 100 R5.5 1/145 ~R5 10/400

Seed Transmission (positive/ tested) Goss’s leaf blight severity and seed infection Goss's severity (%) Growth stage Seed Infection Seed Transmission (positive/ tested) 1 R3 0/200 5 R5 0/755 15 20 R5.25 0/768 35 R5.75 0/145 0/1154 100 R5.5 1/145 0/1233 ~R5 10/400 0/760

Risk factors for Goss’s wilt and leaf blight Percent surface residue Susceptible hybrid Continuous corn Percent surface residue Goss’s wilt in 2011 (Severe storms)

Management in 2012 Resistant hybrid Rotation Residue management

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