Title: Fungicides vs Genetic Resistance for Control of Downy Mildew in Cucumber
1Fungicides vs Genetic Resistance for Control of
Downy Mildew in Cucumber
- Adam Call, Todd Wehner, Peter Ojambo, and Gerald
Holmes - Departments of Horticultural Science
- and Plant Pathology
- North Carolina State University
- Raleigh, NC 27695
- cucurbitbreeding.ncsu.edu
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3Downy mildew disease
- Introduction
- Downy mildew caused by the oomycete pathogen
Pseudoperonospora cubensis - Major foliar disease on cucurbits worldwide
- Downy mildew infects over 50 species of cucurbits
- In approximately 20 genera
- 19 species in the genus Cucumis are hosts
- Important hosts are melon (Cucumis melo),
watermelon (Citrullus lanatus), squash
(Cucurbita) - Epidemics on Cucumis observed in over 70 countries
4Downy mildew pathogen
- Introduction
- Pathogen is an obligate parasite
- Only survives on living plant tissue
- Overwinters in warm regions (or in greenhouses)
- Dispersed by wind and rain
5Downy mildew history
- Introduction
- Main cucumber disease in world production
- Currently and for decades (Europe, Asia)
- Main disease in U.S. until 1940s
- Partially controlled after 1947
- Completely controlled after 1960
- Reappeared in 1988-1989
- Reappeared in 2004-2007
- Less of a problem in NCSU trial plots in 2008
6Downy mildew resistance
- Introduction
- Carroll Barnes (Clemson Univ., Charleston)
- Developed DM resistant cucumber cultivars
- 'Palmetto' slicer (1948) moderately resistant
- 'Ashley' slicer (1956) moderately resistant
- 'Polaris' slicer (1961) highly resistant
- 'Pixie' pickle (1963) highly resistant
- 'Poinsett' slicer (1966) highly resistant
- 'Chipper' pickle (1968) highly resistant
7Downy mildew severity
- Introduction
- Genetic factors
- Host resistance
- Pathogen virulence
- Environmental factors
- Moisture
- Temperature
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9Downy mildew resistance
- Objectives
- Disease resistance
- few lesions
- small lesions
- no chlorotic margins on lesions
- no stunting of plant under disease load
- Disease tolerance
- Yield with vs. without disease
- Combining non-allelic genes
- High resistance (Poinsett)
- Moderate resistance (Ashley)
10Downy mildew resistance
- Methods
- 2 years
- 6 replications
- 3 varieties (SMR18, Sumter, M21)
- 4 fungicide treatments
- None
- Manzate
- BravoPrevicurFlex alt MancozebTanos
- BravoPresidio alt MancozebRanman
- 2 harvests
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12Downy mildew disease rating
- Methods
- Rate component traits
- chlorosis, necrosis, sporulation, stunting
- Rating scale 0 to 9
- 0no damage
- 1-2trace
- 3-4slight
- 5-6moderate
- 7-8severe
- 9dead
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19Downy mildew - 2008 ratings
Variety Fungicide Mean Clr3 Nec3 Snt5 M
21 Tanos 2.3 1.7 2.7 2.5 Mancozeb 2.6 1.5 3.2 3.0
None 3.1 1.8 3.0 4.5 Sumter Tanos 2.2 2.2 3.3 1.
2 Mancozeb 2.6 2.0 4.2 1.7 None 3.4 2.7 5.0 2.5
SMR18 Tanos 4.7 5.7 6.2 2.2 Mancozeb 5.3 7.2 7.2
1.7 None 6.1 7.3 7.5 3.5 LSD (5) 0.7 0.9 1.0 1.
0
20Downy mildew - 2009 ratings
Variety Fungicide Mean Clr3 Nec3 Snt5 M
21 Presidio 2.8 1.8 2.6 4.8 Tanos 3.6 2.8 3.8 5.
2 Mancozeb 3.4 2.4 3.0 5.8 None 4.0 2.8 4.0 6.
8 Sumter Presidio 4.1 3.8 5.2 1.3 Tanos 4.9 4.4
6.0 2.6 Mancozeb 4.9 4.3 5.5 4.3 None 4.9 4.3
5.3 4.8 SMR18 Presidio 5.7 5.8 5.8 3.5 Tanos 6
.2 6.2 6.8 4.2 Mancozeb 6.2 6.1 6.3 5.0 None 6
.7 7.1 6.0 6.3 LSD (5) 0.5 0.8 1.0 0.8
21Downy mildew - 2008 yield
Variety Fungicide cwt/A mkt early M
21 Tanos 81 58 41 Mancozeb 48 48 40 None 17 23 3
6 Sumter Tanos 45 27 11 Mancozeb 17 14 7 None
0 0 0 SMR18 Tanos 10 13 9 Mancozeb 2 0
0 None 0 0 0 LSD (5) 13 17 14
22Downy mildew - 2009 yield
Variety Fungicide cwt/A mkt early M
21 Presidio 59 67 24 Tanos 51 69 28 Mancozeb
21 75 47 None 17 84 52 Sumter Presidio 137 57 20
Tanos 57 23 10 Mancozeb 25 26 14 None 7
0 3 SMR18 Presidio 42 53 29 Tanos
14 45 60 Mancozeb 5 42 22 None 0 0 0 LSD
(5) 3 28 32
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25Control of Downy Mildew-1
- Fungicide - 2008
- Chlorosis (0.7 rating points)
- None-0.3-gtManzate-0.4-gtTnPrv
- Necrosis (1.1 rating points)
- None-0.3-gtManzate-0.8-gtTnPrv
- Yield (39 cwt/A)
- None-16-gtManzate-23-gtTnPrv
26Control of Downy Mildew-2
- Fungicide - 2009
- Chlorosis (0.9 rating points)
- None-0.4-gtManzate-0-gtTnPrv-0.5-gtPrsRn
- Necrosis (0.6 rating points)
- None-0.2-gtManzate-0-gtTnPrv-0.4-gtPrsRn
- Yield (71 cwt/A)
- None-9-gtManzate-24-gtTnPrv-38-gtPrsRn
27Control of Downy Mildew-3
- Genetic resistance - 2008
- Chlorosis (5.0 rating points)
- SMR18-4.6-gtSumter-0.4-gtM21
- Necrosis (4.0 rating points)
- SMR18-2.8-gtSumter-1.2-gtM21
- Yield (45 cwt/A)
- SMR18-17-gtSumter-28-gtM21
28Control of Downy Mildew-4
- Genetic resistance - 2009
- Chlorosis (3.9 rating points)
- SMR18-2.1-gtSumter-1.8-gtM21
- Necrosis (2.8 rating points)
- SMR18-0.7-gtSumter-2.1-gtM21
- Yield (41 cwt/A)
- SMR18-41-gtSumter-0-gtM21
29Control of Downy Mildew-5
- Fungicide plus genetic resistance - 2008
- Chlorosis
- SMR18/None-5.6 rating points-gtM21/Tn
- Necrosis
- SMR18/None-4.8 rating points-gtM21/Tn
- Yield
- SMR18/None-81 cwt/A-gtM21/Tn
30Control of Downy Mildew-6
- Fungicide plus genetic resistance - 2009
- Chlorosis
- SMR18/None-5.3 rating points-gtM21/Pres
- Necrosis
- SMR18/None-3.4 rating points-gtM21/Pres
- Yield
- SMR18/None-137 cwt/A-gtM21/Pres
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32Downy mildew resistance
- Conclusions
- Fungicides 1 rating point better
- 55 cwt/A better
- Genetics 4 rating points better
- 45 cwt/A better
- Combined 5 rating points better
- 100 cwt/A better
33Acknowledgements
- Tammy Ellington, research specialist
- Mike Adams, research specialist
- Jiyoung Oh, visiting scholar
- Mahendra Dia, research assistant
- Adam Call, research assistant
- Laura Arellano, GH assistant
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