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Institute for Ag Professionals Proceedings 2016 Crop Pest Management Short Course & Minnesota Crop Production Retailers Association Trade Show http://www.extension.umn.edu/agriculture/ag-professionals/ Do not reproduce or redistribute without the written consent of author(s).

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Institute for Ag ProfessionalsProceedings

2016 Crop Pest Management Short Course & Minnesota Crop Production Retailers Association Trade Show

http://www.extension.umn.edu/agriculture/ag-professionals/

Do not reproduce or redistribute without the written consent of author(s).

Jim Kurle, Department of Plant PathologyUniversity of Minnesota

St. Paul MN

Soybean Seed, Seedling, and Root Rots: Is Management a Prescription or a Package?

• Seedling Diseases• The Disease and the Pathogen• Status in Minnesota• Resistance Resources• Management Resources

Phytophthora sojae and Pythium spp.

Second to sixth among diseases that suppressed soybean yield from 1996 to 2007 Influenced by spring planting season moisture

conditions Phytophthora – up to 6% annually Pythium, Fusarium, Rhizoctonia, Phomopsis – up

to 6% annually: Sensitive to environment

(Wrather & Koenning, 2009)

Seed and Seedling Diseases

Background• Seed constitutes a large percentage of input cost• Farmers are planting earlier each year.• Risk of stand loss increases with early planting date, no

till, wet conditions

D. Malvick (PHI, U of Wisconsin)

Soybean production costs in IA

(Iowa Farm Business Association)

Input costs increased 87% (2003 to 2010)

Seed costs increased 100% (2003 to 2010)

Cos

t ($)

Seedling diseases most often encountered (past 5 yrs)

Commonly Occasionally Rarely Never

Fusarium root rot 5.5 44.1 38.1 6.7

Phomopsis seed decay 1.0 15.3 44.2 22.3

Phytophthora root rot 33.2 51.6 11.9 1.2

Pythium root rot 28.4 51.3 16.6 1.5

Rhizoctonia root rot 18.0 49.6 26.3 2.3

Unidentified seedling disease 4.4 31.5 33.6 6.3

(Arbuckle & Robertson, 2012)

Pythium spp.

Rhizoctoniasolani

Fusariumspp.

Phytophthorasojae

oomycetes fungi

(A. Robertson, ISU)

OomycetesPhytophthora sojae,

Pythium species

• Cell wall composed of cellulose

• No cross walls in hyphae• Diploid nuclei in vegetative

state• “Swimming” spores• More closely related to

brown algae and diatoms

True fungiFusarium species, Rhizoctonia solani

• Cell wall composed of chitin

• Cross walls in hyphae• Haploid nuclei in vegetative

state• Air- or splashed- dispersed

spores• More closely related to

animals

The Soybean Root Rot Complex

Rhizoctonia

Phytophthora

Sudden Death Syndrome

Pythium

Fusarium

Fusarium

(adapted from Grau et al.,2004; Hanson et al., 2000; Irmak et al., 2006, Meyer, 2011)

Temperature and Moisture Effect on Infection

Phytophthora Root Rot –Seedling Rot & Damping Off

Disease Symptoms

post-emergencedamping-off

http://www.planthealth.info/prr_basics.htm

root & stem rot

Phytophthora Root and Stem Rot• Causal agent: Phytophthora sojae Kauf. & Gerd.• Widespread in soybean growing areas of the US and

worldwide (Canada, Australia, Queensland, & East Asia).

• 2nd most damaging disease to soybean in north central US from 1996-1998.

• Annual yield loss: 42,218,000 bu in US in 1998• Minnesota losses average ~ 1.0% of yield.• On individual field basis losses of 50 to 60%.

P. sojae Life Cyle

http://www.apsnet.org/edcenter/intropp/lessons/fungi/Oomycetes/Pages/PhytophthoraSojae.aspx

St. Louis

Martin Faribault Freeborn Mower Fillmore Houston

Murray Watonwan

Winona

Nobles JacksonRock

Lyon Redwood

BrownNicollet Rice

Wabasha

SibleyScott DakotaYellow Medicine Renville

Carver

LacQuiParle

Chippewa

Kand

iyoh

i

Meeker WrightAnoka

Chis

ago

IsantiSherburne

Stearns

Swift

Big Stone

PopeTrav

erse Grant Douglas

Todd Morrison

Mill

e La

cs

Pine

Otter Tail

Clay

Wad

ena

Becker Cass

Crow

Wing

Aitkin Carlton

Norman Mah-nomen

Polk

Red Lake

Pennington

Marshall

Kittson RoseauLake

of the

Woods

BeltramiKoochiching

ItascaLake

Cook

Clea

rwat

er

Phytophthora sojae Found in 2000

Phytophthora sojae races (pathotypes)

Rps gene (s)

1 3 4 7 25 31

Rps1a R S S S S RRps1c R R S R S RRps1k R R R R S SRps3a R R R S R RRps6 R R R S R SRps8 R R R R R R

Race Pathotype

1

3 1a

4 1a, 1c

7 1a, 3a, 6

25 1a, 1c, 1k

31 1k, 6

Race vs Pathotype

Resistance genes

1 3 4 6 25

Rps1a R S S S SRps1b R R R R SRps1c R R S R SRps1k R R R R SRps3 R R R S RRps6 R R R S R

Phytophthora races Found In Minnesota in 1984

Race ---------------------------------Pathotype---------------------------------1 Rps02 Rps0 Rps1b3 Rps0 Rps14 Rps0 Rps1, Rps1c

6 or 7 Rps0 Rps1, Rps3, Rps4, Rps68 or 9 Rps0 Rps1, Rps4, Rps6

13 Rps0 Rps615 Rps0 Rps318 Rps0 Rps1c21 Rps0 Rps1, Rps322 Rps0 Rps1, Rps1c Rps3, Rps4, Rps625 Rps0 Rps1, Rps1b Rps1c Rps1k27 Rps0 Rps1b Rps1c Rps1k Rps 3, Rps4, Rps628 Rps0 Rps1, Rps1b Rps1k Rps431 Rps0 Rps1b Rps1c Rps1k Rps4, Rps645 Rps0 Rps1, Rps1b Rps1c Rps1k Rps4, Rps6ND Rps0 Rps1, Rps1kND Rps0 Rps1, Rps1c Rps6ND Rps0 Rps1b Rps1k Rps3, Rps6ND Rps0 Rps1, Rps1c Rps1k Rps4, Rps6ND Rps0 Rps1c Rps1k Rps 3, Rps6ND Rps0 Rps1, Rps1c Rps1k Rps3, Rps4, Rps6ND Rps0 Rps1, Rps1b Rps1c Rps1k Rps3, Rps4 Rps6

Phytophthora races Found In Minnesota in 2000

Change in number of Phytophthora sojaepathotypes identified in Minnesota

0

10

20

30

40

50

60

70

80

90

1984 2000 2012

Pathotype

Proportion of P. sojae Isolates Virulent on Major Resistance Genes

Rps Genes Defeated by Isolates found in Minnesota - 2012

Within Field Diversity of P. sojae

Rps3a Rps1c Rps1k

(Dorrance, 2007)

Diversity : Horizontal and Vertical P. sojae within a single field is highly diverse.

Location 1: 21 isolates belonging to 10 races and nine pathotypes were recoveredLocation 2: a total of 13 isolates of P. sojae belonging to nine races and three pathotypes

P. sojae population within the root zone can be diverse.

In a single soil sample: Isolate 1, able to defeat Rps1a, 3a, and 7; Isolate 2, defeats Rps1a, 1d, 1k, 3a; Isolate 3 defeats Rps1c and 7; and Isolate 4 defeats Rps1a, 1k, 4, 6, and 7.

(Robertson et al., 2007)

Qualitative Resistance

Resistance genes (Rps genes)• 14 Rps genes identified

-Rps1a, Rps1b, Rps1c, Rps1d, Rps1k, Rps2, Rps3a, Rps3b, Rps3c, Rps4, Rps5, Rps6, Rps7, & Rps8

• 9 Rps genes deployed into commercial cultivars-Rps1a, Rps1b, Rps1c, Rps1k, Rps2, Rps3a, Rps4, Rps6, & Rps7

Susceptible(S)

Resistant(R)

Reaction Types

Partial Resistance to P. sojae

1 to 2 3 to 4 5 to 6 7 to 8 9 to 10

1 to 2--- Healthy, no symptoms.3 to 4--- Slight discoloration of secondary roots to first signs of pruning of secondary roots.5 to 6--- Pruning of secondary roots to first appearance of lesions on primary root.7 to 8--- Secondary roots essentially absent. Lesions present on primary root and tip pruning.9 to 10-- Damping of seedling. Dead seedling. Rotted seed.

0.00

2.00

4.00

6.00

8.00

10.00

Cultivar

Roo

t Rot

Rat

ing

HIJIJ

JK

KL

L LKL

(P ≤ 0.05)

Root Rot Rating of 28 Soybean Cultivars Evaluated for Partial Resistance

Partial Resistance

• More durable than resistance (Rps genes) -non race-specific-not affected by shifts in race composition of P. sojae-exert no selection pressure on P. sojae population

• Why have not been widely used? -hard to incorporate into cultivars -polygenic, quantitative trait

-identify QTLs before incorporating into cultivars

Managing Phytophthora sojae

• Cultural practices: -crop rotation, soil drainage, tillage

• Planting resistant cultivars (Rps genes)

• Planting partially resistant cultivars

• Chemicals: metalaxyl, mefanoxam, ethaboxam-seed treatment, in-furrow application

Pythium spp.

• The Pathogen• Status in Minnesota• Resistance Resources• Fungicide Efficacy• Integrated Management

Pythium Symptoms

Post emergence damping off

Stem lesion caused by Pythium

(Photos, XB Yang, ISU)

Identities and frequencies of Pythium and Phytopythium species isolated from seedling and soil samples collected in soybean fields in Minnesota.

(Radmer et al., 2016)

Growth of Pythium and Phytopythium species on PDA amended at three concentrations with either A) ethaboxam, B) mefenoxam, or C) trifloxystrobin.

Sensitivity to fungicides varies among Pythium species

ethaboxam mefenoxam trifloxystrobin

(Radmer et al., 2016)

Growth of Pythium and Phytopythium species on PDA amended at three concentrations with either A) azoxystrobin, B) pyryclastrobin, or C) trifloxystrobin.

Sensitivity to fungicides varies among Pythium species

(Radmer et al., 2016)

azoxystrobin trifloxystrobinpyryclastrobin

Pythium spp. infecting soybean in MN

(Radmer et al., 2016)

Pythium spp. infecting corn in MN

(Radmer et al., 2016)

• The number of Pythium species complicates utilization of resistance

• Resistance to Pythium spp.has been identified in soybean cultivar “Archer” (MG-IV)and in PI424354

• Resistance to different Pythium species is not correlated

• Cultivar resistance to Pythium is not yet a reality

Cultivar Resistance to Pythium

Active ingredient

Phytophthorasojae

Pythiumspecies

Rhizoctonia solani

Fusariumspecies

mefenoxam/metalaxyl

E E N N

azoxystrobin N P F Ffludioxonil N N G Gipconazole N P F G

pyraclostrobin N P F Ftrifloxystrobin N P F F

sedoxane N N E G(ethaboxam) E E N N

E = excellent; G = good; F = fair; P = poor N = none(Adapted from K. Wise, NCSRP, 2016)

Fungicide Seed Treatments

• Crop Rotation– Limited effectiveness, oospores persist

• Promote Drainage • Minimize Compaction• Disease Resistance

– Effective for Phytophthora, less so for Pythium spp.

• Seed Treatment– Mefanoxam, Metalaxyl, and now Ethaboxam

Managing Diseases Caused by Oomycetes

• Funding for supporting studies provided by MSRPC, NCSRP,USB, and MAES.

Acknowledgements

• Bradley, C. (University of Illinois) • Chase, T. (South Dakota University)• Chilvers, M. (Michigan State University)• Esker, P. (University of Wisconsin) • Giesler, L. and Lee, D. (University of Nebraska)• Jardine, D. (Kansas State University)• Malvick, D. and Kurle, J. (University of Minnesota)• Markell, S. and Nelson, B. (North Dakota State University)• Robertson, A. and Arbuckle, J. (Iowa State University)• Rupe, J. (University of Arkansas) • Sweets, L. (University of Missouri) • Wise, K. (Purdue University)

Web newsletters

The Plant Health Initiative: http://www.planthealth.info/

ICM News: http://www.extension.iastate.edu/CropNews

Minnesota Crop Diseases: http://www.extension.umn.edu/cropdiseases/

The Bulletin:http://www.bulletin.ipm.illinois.edu

Wisconsin Crop Manager: http://ipcm.wisc.edu/

Additional Resources