CP 157 Aerial oomcycetes review

174 Pages·2016·2.11 MB·English

Project title: Aerial Oomycetes: Assessing Management and Control
Options Needed in UK Edible & Ornamental Crops

Project number: CP 157

Project leader: Erika F. Wedgwood

Report: Final Review

Previous report: N/A

Key staff: Matthew Hamilton (ADAS)
Erika Wedgwood (ADAS)
Matthew Cromey (RHS)
John Scrace (RHS)
Geoff Denton (RHS)
Celia Van Sprang (ADAS)
Tim O’Neill (ADAS)
Tim Pettitt (University of Worcester)
Peter Gladders (ADAS)
David Talbot (ADAS)
Jill England (ADAS)
Angela Huckle (ADAS)
Sarah Mayne (ADAS)
Chris Creed (ADAS)
Janet Allen (ADAS)

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Locations of project: ADAS UK Ltd
ADAS Boxworth
Battlegate Road
Boxworth
Cambridge
CB23 4NN

The Royal Horticultural Society
Wisley
Woking
Surrey
GU23 6QB

University of Worcester
NPARU
Charles Darwin Building
University of Worcester
Henwick Grove
Worcester
WR2 6AJ

Industry Representative: Karl O'Neill, Bransford Webbs,
The Bransford Webbs Plant Company
Bransford
Worcester
WR6 5JN

Date project commenced: 1 October 2015

Date project completed: 31 March 2016
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DISCLAIMER

While the Agriculture and Horticulture Development Board seeks to ensure that the
information contained within this document is accurate at the time of printing, no warranty is
given in respect thereof and, to the maximum extent permitted by law the Agriculture and
Horticulture Development Board accepts no liability for loss, damage or injury howsoever
caused (including that caused by negligence) or suffered directly or indirectly in relation to
information and opinions contained in or omitted from this document.

© Agriculture and Horticulture Development Board 2016. No part of this publication may be
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AUTHENTICATION

We declare that this work was done under our supervision according to the procedures
described herein and that the report represents a true and accurate record of the results
obtained.
Erika Wedgwood
Project Leader, ADAS

Signature Date 31 March 2016

Matthew Cromey
Project Collaborator, RHS
Signature Date 31 March 2016

Report authorised by:
Barry Mulholland
Head of Horticulture, ADAS

Signature Date 31 March 2016

Gerard Clover
Head of Research, RHS

Signature Date 31 March 2016
 Agriculture and Horticulture Development Board 2016. All rights reserved
CONTENTS
GROWER SUMMARY ............................................................................................... 1
Headline.................................................................................................................. 1
Background ............................................................................................................. 1
Summary ................................................................................................................ 1
Host range ..................................................................................................................... 2
Biology .......................................................................................................................... 2
Integrated Crop Management ........................................................................................ 2
Financial Benefits ................................................................................................... 3
Action Points ........................................................................................................... 4
SCIENCE SECTION .................................................................................................. 7
Introduction ............................................................................................................. 7
References .................................................................................................................... 9
Aims and Objectives ............................................................................................. 11
Materials and methods ......................................................................................... 11
Life Cycles ............................................................................................................ 13
Reference ............................................................................................................. 14
Possibilities of spread of predominantly airborne oomycetes via contaminated
irrigation water ...................................................................................................... 14
References ........................................................................................................... 15
Elicitors: an overview of their mode of action ........................................................ 16
Introduction ........................................................................................................... 16
Types and pathways of elicitation agents .................................................................... 16
Degree of elicitation can vary with host genotype ........................................................ 18
Potential drawbacks of elicitors ................................................................................... 19
Conclusion ............................................................................................................ 19
References ........................................................................................................... 20
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Changes affecting the incidence and severity of aerial oomycete diseases ......... 21
Fungicide resistance in aerial oomycetes and product availability ............................... 21
Invasive pathogens ..................................................................................................... 24
References ........................................................................................................... 25
Edible Crop Reviews ............................................................................................ 25
Vegetable Brassica Downy Mildew .............................................................................. 25
References ........................................................................................................... 29
Vegetable Brassica White Blister ................................................................................. 31
References ........................................................................................................... 34
Onion Downy Mildew ................................................................................................... 36
References ........................................................................................................... 38
White Tip of Leeks ....................................................................................................... 38
References ........................................................................................................... 40
Pea Downy Mildew ...................................................................................................... 41
References ........................................................................................................... 43
Broad Bean Downy Mildew .......................................................................................... 44
References ........................................................................................................... 45
Cucumber Downy Mildew ............................................................................................ 45
References ........................................................................................................... 49
Tomato Late Blight ...................................................................................................... 51
References ........................................................................................................... 54
Wild and Salad Rocket Downy Mildew ........................................................................ 55
Red Beet Downy Mildew ............................................................................................. 56
Rhubarb Downy Mildew ............................................................................................... 58
References ........................................................................................................... 59
Blackberry Downy Mildew............................................................................................ 59
References ........................................................................................................... 62
Apples and Pear Phytophthora Fruit Rot ..................................................................... 63
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References ........................................................................................................... 64
Downy Mildew of Herbs ............................................................................................... 65
Basil ...................................................................................................................... 66
Sage ..................................................................................................................... 67
Parsley .................................................................................................................. 68
Chives ......................................................................................................................... 68
Mint ............................................................................................................................. 69
References ........................................................................................................... 69
Ornamental Plants Review ................................................................................... 71
Aerial Phytophthora on Ornamental and Amenity Trees and Shrubs ........................... 71
References ........................................................................................................... 75
Antirrhinum Downy Mildew .......................................................................................... 77
References ........................................................................................................... 79
Aquilegia Downy Mildew .............................................................................................. 80
References ........................................................................................................... 81
Hebe Downy Mildew .................................................................................................... 81
References ........................................................................................................... 84
Impatiens Downy Mildew ............................................................................................. 84
References ........................................................................................................... 86
Lisianthus (Eustoma) Downy Mildew ........................................................................... 87
References ........................................................................................................... 88
Nicotiana Downy Mildew ............................................................................................. 88
References ........................................................................................................... 90
Poppy Downy Mildew .................................................................................................. 91
References ........................................................................................................... 93
Pansy and Viola Downy Mildew ................................................................................... 94
References ........................................................................................................... 96
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Rose Downy Mildew .................................................................................................... 96
References ........................................................................................................... 99
Senecio cineraria White Blister .................................................................................. 100
References ......................................................................................................... 102
Summary tables of common UK pathogens, knowledge areas and gaps ........... 103
AHDB Funded Research on Aerial Oomycete Pathogens (Edible Crops) .......... 110
AHDB Funded Research on Aerial Oomycete Pathogens (Ornamental Plants) . 123
References ......................................................................................................... 128
Grower survey responses ................................................................................... 130
Grower overview of potential issues with aerially sporulating oomycetes in
propagation and methods used on a nursery for pathogen control. .................... 134
Downy mildew ........................................................................................................... 135
White blister .............................................................................................................. 136
Biofungicides ............................................................................................................. 136
Agronomist overview of prevalence and problems in edible crops in the UK ...... 137
Crop Consultants’ evaluation of aerial oomycete prevalence in the UK on edible and
protected ornamental crops and potential crop losses ........................................ 140
Discussion............................................................................................................ 143
References ......................................................................................................... 147
Conclusions ......................................................................................................... 148
Host range ................................................................................................................. 148
Biology ...................................................................................................................... 148
Integrated Crop Management .................................................................................... 148
Knowledge and Technology Transfer ................................................................. 149
Appendices .......................................................................................................... 150
Appendix 1. Table of useful websites ........................................................................ 150
Appendix 2. Knowledge Exchange; grower evaluation of various methods ................ 152
Appendix 3. Grower Survey Form .............................................................................. 153
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Appendix 4. Contents of CP 126 – A desk study to review global knowledge on best
practice for oomycete root-rot detection and control. ................................................. 162
Appendix 5. Information on oomycete pathogens on the UK Plant Health Risk Register
.................................................................................................................................. 163

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GROWER SUMMARY
Headline
Developments in spore detection, disease forecasting and biological treatments are aiding
progress towards development of effective IPM strategies for aerial oomycete pathogens, but
more work is needed.
Key knowledge gaps remain in our understanding of these pathogens, with implications for
their control.
Background
Downy mildews, white blisters and certain Phytophthora species are examples of oomycete
pathogens which can be transmitted aerially and infect above ground plant tissue. The
oomycetes are a group of fungus-like organisms that can cause economically significant
losses on a wide range of plant species. They can exist as a range of structures throughout
their lifecycle, enabling them to persist aerially, in water and in soil.
Economically significant losses due to oomycetes occur across the majority of horticultural
production systems. They are often considered to be fairly ubiquitous in the environment, with
most aerial oomycetes also able to persist in soil and growing media as either mycelium or
oospores. Temperatures between 5-25°C (varying for individual pathogens) favour diseases
caused by oomycete pathogens, with white blister pathogens in general favouring slightly
higher temperatures than Phytophthoras and downy mildews. The correct temperature
coupled with high humidity and/or foliage wetness can lead to the rapid spread of oomycete
diseases throughout a crop once present. There has been recent industry concern over
downy mildews new to, or not previously a problem in the UK, including on basil, impatiens
and aquilegia and also aerial Phytophthora species including P. ramorum.
Summary
Information on the main aerial oomycete diseases of horticultural crops, determined by a
survey to be currently important to UK growers, was obtained from recent UK and overseas
research. In addition to published journals, the outcomes of relevant AHDB projects were
evaluated. This review highlights research that has provided new understanding of the
pathogens and measures for their control, and the gaps in knowledge remaining. Future
threats including pesticide resistance and emerging disease problems were reported. Areas
for further investigation related to host range, biology and disease management are itemised
below. Thirteen crop-specific reviews of edibles and 11 of ornamentals were carried out and
key areas of knowledge for the principal pathogens are tabulated below.
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