using physiological and horticultural principles to create superior
TRANSCRIPT
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Management practices for control of soilborne pathogens in UC strawberry
cultivars
Kirk LarsonUC Davis / UC South Coast REC
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Low-ElevationNurseries
High-Elevation Nurseries
Watsonville/Salinas
Santa MariaOxnard
Orange CountySan Diego
Central Valley
CoachellaValley
California strawberry nursery and fruit
production regions
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Major strawberry soilborne pathogens
Phytophthora cactorum root & crown rotVerticillium dahliae
Macrophomina phaseolinaFusarium oxysporum
Colletotrichum acutatum* root & crown rotBotrytis* petiole, crown and root rot
Viruses and phytoplasms** Technically not soilborne pathogens
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Superior plant quality starts in the nursery…- Pest- and disease-free plants
(meristem culture, soil fumigation, BMPs) - Location, soil type, dig date, handling- Physiological conditioning (chill, CHO+N levels)- Plant size / development
…but does not end there- Plant selection, postharvest handling, transport- Establishment conditions, methods- Fruiting field BMPs
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Heat treatment
Suppresses viruses and other pathogens
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Disease-freemeristem
plant
Photo courtesy C. Gaines
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Meristem Propagation
- Eliminates plant pathogens
- Enhances plant vigor
- Plants derived from meristem culture willremain pathogen-free if kept isolatedfrom sources of contamination (attention to sanitation, BMPs)
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Screenhousepropagation
Each meristem plant produces
100-200 daughter plants
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Foundation Block - Isolation
Photo courtesy C. Gaines
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Low elevation increase nursery
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Nursery development September 1
High elevation nursery planted April 1
(~10k mother plants/A)
Low elevation nursery planted late May - June(<2k mother plants/A)
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California nurseries ship plants worldwide
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Generational increase in plant numbers from one meristem
1 meristem plant 100 Screenhouse daughters100 Foundation plts X 100 10,000 daughters10,000 LE increase plts X 100 1m daughters1m HE increase plts X 30 30m daughters
1 meristem plant can easily generate 30,000,000 plants in four years
Pathogens or off-types can become explosive!
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Breeding for disease tolerance/resistance
Helpful & desireable, but not a complete solution:
- high inocula levels can overcome resistance
- resistance to all major pathogens is statistically impossible
A combination of horticultural management and resistance breeding is likely to be most
effective way to minimize harmful effects of soilborne pathogens
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Disease resistance scores for UC short-day cultivars, 2004-07
Resistance score: 5 = most resistant
Phytophthora Verticillium C. acutatumresistance resistance resistance
Genotype (5 = best) (5 = best) (5 = best)
Camarosa 3.6 2.5 2.6
Camino R 4.4 4.2 3.1
Ventana 2.5 3.0 3.0
Palomar 2.4 3.3 3.2
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Disease resistance scores for UC day neutral cultivars, 2004-07
Phytophthora Verticillium C. acutatumresistance resistance resistance
Genotype (5 = best) (5 = best) (5 = best)
Albion 4.3 3.8 3.4
Monterey 3.2 3.4 2.4
S. Andreas 3.8 3.8 2.9
Portola 4.4 3.3 2.7
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Phytophthora cactorum in HE nursery
Pythium and Phytophthora are in same general class of fungi
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Phytophthora cactorum in fruiting field
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Phytophthora/Pythium control strategies
- Choose well-drained soils and sites – avoid heavy soils and low-lying areas
- Deep rip 3-4 ways
- Pre-plant soil fumigation using the most
effective compounds available
- Pre-plant dip with Aliette, Phosgard, etc.
- Regular applications of Phosgard, Ridomil,
Aliette
- Irrigate appropriately
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Phosphorous acid materials
Phosphorous acid (H3PO3, Phosguard, etc.) dissociates into phosphite ion (HPO3
-2)Phosphite readily taken up/translocated in plant
but is not converted to phosphate (nutrient) Phosphite contributes little or nothing to P
nutrition of plantPhosphorous acid fungicides are effective
against water molds (Oomycetes) such as Phytophthora and Pythium
Are stable in plant, apply infrequently (~1x/month)
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Phos- 12# C/A to Size App FirmItem gard 3/1 4/1 6/1 (g) (1-5) (1-5)
Camarosa Yes 1355 2601 8492 30.8 2.6 3.5No 999 2250 8478 30.6 2.6 3.4
Palomar Yes 1562 3258 8001 30.1 3.8 3.8No 1409 2876 7511 30.4 3.8 3.8
Ventana Yes 1031 2965 8532 30.7 3.4 3.6No 990 2880 7839 29.8 3.4 3.5
* Phosguard applied as a pre-plant dip, then at monthly intervals through the drip irrigation system
Performance of SD cultivars with or without Phosguard treatments*, Irvine 2006-07
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Verticillium in HE transplants
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Fumigated and non-fumigated runner nursery plots
Verticillium wiltNo Verticillium wilt
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InLinefumigated *HE nursery
plot
NoteVerticilliumsymptoms
*445#/a of 2:1 (wt:wt) Telone:chloropicrin
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Verticillium control strategies
Avoid crop rotations that include tomato, potato, alfalfa, cotton, olive
Use preplant soil fumigation with highest possible rates of the most-effective fumigants
In strawberry nurseries, apply fumigants in fall rather than in spring
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Non-treated Vapam Chloropicrin
Methyl bromide alternatives
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Transplants fromnon-fumigatednursery with no
detectable
pathogens
Transplants from MBPic-fumigated
nursery
Nursery soil fumigation
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Macrophominaphaseolina
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M. phaseolinaWide host range Prefers warm, dry soil
Variable cultivar susceptibility
2009: Genetic screen (Larson, Gordon, Koike, Shaw)
Flat fume with MBPic to eliminate all pathogensEstablish plants of Albion, inoculate with MpIncorporate inoculated plants into soil Establish 50+ HE cultivars and selectionsRate plant vigor and survival
Also in 2009: Implement fungicide efficacy trials
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Establish Albionplants in fumigated
soil
Inoculate with Mp
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Inoculation, infection
andincorporation
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Infested plots
Control plots
Establish replicated plots in clean
and infested soil
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Strategies for controlling Macrophomina
Choose colder sites (?)
Avoid soil water-stress
Anecdotal evidence suggests differences in varietal susceptibility
Topsin applications may help suppress Mp
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Fusarium oxysporum
Genetic screen similar to Macrophomina screenis being developed by D. Shaw and T. Gordon
at UC Davis
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C. acutatumNot a true soil pathogen
Can cause root and
crown infection
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Transplants infected withC. acutatum
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Colletotrichum acutatum Fruit & flower infection in fruiting field
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C. acutatum control strategies
Pre-plant hot-water dip in low-elevation nurseries
Pre-plant fungicide dip (Abound, Rovral, Topsin, etc.)
Apply foliar fungicides on a routine basis
Move workers from clean to infected fields
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Control WashWash +
Quadris dip
Preplant fungicide dip for control ofC. acutatum and other diseases in
nurseries and fruiting fields
Reduces pathogen levels, re-hydrates plants
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C. acutatum genetic screen
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C. acutatum genetic screen
Cultivar Parent info selection
Sweet Charlie
‘05 selection‘05 selection
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Drip-irrigated runner nurseries
Nursery drip irrigation used at SCFS since 1998Reduces incidence of certain pathogens
Periodic sprinkler irrigation to manage soil salinity
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Phytoplasms
Leafhopper-vectored
Multiplier disease
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Viruses
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Virus complexes
Vectors: aphids, whitefly, leafhoppers
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Control strategies for viruses and phytoplasms
Use systemic and contact insecticides to controlaphids, leafhoppers, whitefly:
Admire, Esteem, Disyston, Malathion+Danitol
Eliminate weeds that can be host plants
Isolation from other strawberry plantings
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Botrytis fruit rot
Also: Botrytis petiole, crown and root rot
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New UC strawberry (Pomology) website:
http://www.plantsciences.ucdavis.edu/ucstrawberry
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THANK YOU!