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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)
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
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
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
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
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
• 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
• 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