benson fighting phytophthora 08
DESCRIPTION
2008 APS meeting, Phytophthora WorkshopTRANSCRIPT
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Two simple inoculation methods for Phytophthora blight and root rot studies
Mike BensonNC State University
Raleigh
NC STATE Ornamental Pathology
Steve TjosvoldUniversity of California Cooperative Extension,
Watsonville
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Trial
Hinodegiri azalea
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Phytophthora inoculum
• Rice grain method– 25 g long grain rice– 18 ml deionized water– Autoclave 40 min
Holmes, KA and Benson, DM. 1994Plant Disease 78:193-199.
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Next day
• ‘Stir up’ rice mat with bent rod
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Loosen mat & separate grains
• Autoclave 2nd time: 40 min
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Rice grain method
• Transfer agar disks
How many rice grains?
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‘Bump flask’ each day
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Uncultured rice 14-day-old culture
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Culture audit
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Local inoculum placement
• Whole rice grains– Host/Cultivar evaluations– Fungicide trials– Pathogenicity tests
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2 grains/hole; 3 holes/pot
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Inoculation time: approx. 60 plants/person/hour
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Foliar ratings
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Foliage symptoms: root rot
Rating = 1
Rating = 3
Scale: 1 = Healthy; 4 = Dead
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Root symptoms
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Controls
NC STATE Ornamental PathologyHinodegiri azalea
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Root rot rating
• 1= healthy, full root ball,• 2= some root rot, less than full root ball, • 3= severe root rot, 50% of root system
necrotic, • 4= very severe root rot, root ball falls
apart, • and 5 = plant dead, all roots necrotic.
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Year to year: consistency
1.0 c2.09 ab1.4 e1.3 f1.1 cSprayAliette 80WP 80 oz . . . . . . . . . . . . . . . .
2.9 b0.59 d2.9 b2.9 bc2.4 bzUntreated control . . . . . . . . . . . . . . . . .
Sep 7Aug 18Jul 20
Rootroty
Top wt(oz)
Foliar rating
ApplicationTreatment and Rate/100 gal
1.0 c1.74 ab1.6 cde1.6 def1.0 cNon-inoculated control . . . . . . . . . . . . .
2006
1.2 c2.2 abc1.2 c1.0 bSprayAliette 80W 80.0 oz. . . . . . . . . . . . . . .
3.0 a0.7 e 3.0 a2.4 a xUntreated control . . . . . . . . . . . . . . . . . . .
oz09 Sep22 Jul
Root rot(1-5)y
Top wtDisease severityz
ApplicationTreatment and rate /100 galapplied at a 30-day interval
2004
1.0 c2.3 abc1.0 c1.2 bNon-inoculated control . . . . . . . . . . . . .
Hinodegiri azalea
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Rice grain no. & Disease
3.2 a7 b9 rice gr/pot
2.0 ab18 ab6 rice gr/pot
1.8 ab25 a3 rice gr/pot
2.6 ab25 a1 rice gr/pot
1.2 b29 aUntreated
Root rot(1-5)
Top wt.(g)Treatment
Hinodegiri azalea: June 6 – September 19, 2006
Pot volume = 2.5 L
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Uniform inoculum placement
• Rice grain particles– Pre- & post-emergence damping-off studies
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Pulverize & Sieve
No. 10 sieve with 2-mm-openings
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Weigh inoculum
• How much to use?– Trial & error
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Adding carrier
• Surface applications
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Blending carrier & inoculum
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Seed & Cover
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Pre-emergence damping-off
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Did you notice the rice color change?
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Rhizoctonia solani
• Pythium and Thielaviopsis
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Foliar inoculation chamber• Steve Tjosvold
– University of California Cooperative Extension, Watsonville
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Chamber features
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Chamber close-up
• Inoculum– Mycelial disk– Spore suspension
• 5,000 zoospores/cap
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Chamber in place
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In the field
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Wounding
• More consistent– Uniform infection
circular, 6-mm-diameter, fine wire brush
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Uses
• Pathogenicity tests• Fungicide trials• Environmental studies• Hosts/cultivar evaluations
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Questions?