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Hangzhou Foods
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NY9406 Downy Mildew on seedlings - factsheet
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Parsley Disease Handbook
Parsnip Variety Trials
Phytochemical composition of food
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Reclaimed water use in Victoria
Recycled Water Quality - Lettuce
Sclerotina - Lettuce Conference 2002
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Summer Root Rot in Parsley
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Vegetable Disease Program
Vegetable Diseases in Australia
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VG00013 Leek Diseases
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VG00031 Peas - downy mildew & collar rot
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VG00044 Clubroot - Applicator design
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VG00044 Clubroot – Introduction
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VG00044 Clubroot – Prevention & Hygiene
VG00044 Clubroot – Understanding Risk
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VG00048 Alternate fungicides for sclerotinia control
VG00048 Brassica green manure conference paper 2004
VG00048 Brassica Green Manure Update 16
VG00048 Brassica Green Manure Update 18
VG00048 Diallyl Disulphide - DADS - trials
VG00048 Lettuce - Sclerotinia biocontrol
VG00048 Lettuce Sclerotina - Biocontrols
VG00058 Pea - Collar Rot
VG00069 Cucumber & Capsicum diseases
VG00084 Beetroot for Processing
VG01045 Bunching Vegetables - disease control
VG01049 Compost - Benefits
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VG01049 Compost - Getting Started
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VG01049 Safe Use of Poultry Litter
VG01082 Broccoli Adjuvant Poster
VG01082 Broccoli Head Rot
VG01096 Article - White Rot research
VG01096 Integrated Control of Onion White Rot
VG01096 Poster - Alternative fungicides
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VG02020 Capsicum - Sudden Wilt
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VG02105 Vegetable Seed Dressing Review
VG02118 White Blister
VG03003 Lettuce - Varnish Spot
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VG03100 Retailing Vegetables - Broccolini®
VG04010 Maximising returns from water
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VG04013 Brassica White Blister
VG04013 White Blister - Control Strategies
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VG04014 Better Brassica
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VG04014 Clubroot Guidebook
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VG04019 Nitrate & Nitrite in Leafy Veg
VG04021 Vegetable Seed Treatment
VG04025 Parsley Root Rot
VG04059 Diagnostic test kits
VG04061 White Blister - alternative controls
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VG04062 Beetroot Study Tour
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VG05014 IPM - Native vegetation pt1
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VG05045 Parsnip Canker
VG05051 Climate Change
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VG05068 Baby Leaf Salad Crops
VG05073 Mechanical Harvesting
VG05090 Green Bean - Sclerotinia
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VG06014 Revegetation for thrip control
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VG06046 Parsley Root Rot
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VG06066 LOTE Grower Communications
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VG06092 Pathogens - Gap Analysis
VG06092 Pathogens of Importance - poster
VG06140 Beetroot - colour quality
VG07010 Systemic aquired resistance
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VG07070 Conference Notes 2008
VG07070 Foliar diseases
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VG07070 Predicting Downy Mildew on Lettuce
VG07070 White Blister - Chinese Cabbage
VG07070 White Blister - Cultural Controls
VG07070 Workshop Notes - 2008
VG07070 Workshop Notes - 2010
VG07125 IPM - soilborne diseases
VG07126 Biofumigation oils for white rot
VG07126 New approaches to sclerotina
VG07127 White Blister - Alternative Controls
VG08020 Optimising water & nutrient use
VG08026 Pythium - field day
VG08026 Pythium - workshop 2010
VG08026 Pythium control strategies - overview
VG08107 - Carbon Footprint - workshop
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VG08426 Parsnip - Pythium Notes 2010
VG09086 Evaluation of Vegetable Washing
VG09159 Grower Study Tour- Spring Onions & Radish
VG96015 Carrot Crown Rot
VG96015 Carrot Defects - Poster
VG97042 Export - Burdock, Daikon and Shallots
VG97051 Pea - ascochyta rot
VG97064 Greenhouse Tomato and Capsicum
VG97084 Green Bean - white rot
VG97103 Celery Mosaic Virus
VG98011 Carrot - Cavity Spot
VG98048 Lettuce - Adapting to Change
VG98083 Lettuce - rots & browning
VG98085 GM Brassicas
VG98093 Microbial hazards - review
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VG99005 Quality wash water
VG99008 Clubroot - rapid test
VG99016 Compost and Vegetable Production
VG99030 Globe Artichokes - value adding
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VG99057 Soil Health Indicators
VG99070 IPM - Celery
Victorian soil health
VN05010 Folicur - alternative carriers
VN05010 Onion White Rot - Fungicides
VN05010 Onion White Rot - summary
VX00012 Metalaxyl breakdown
VX99004 Clean & Safe Fresh Vegetables
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VG98083 Lettuce - rots & browning

Rots and browning reduce the visual quality of the produce especially in fresh cut products.

Minor discolouration leads to loss of consumer appeal whilst majorr problems lead to rejection of the product

An investigation into the role of bacteria on rots and browning of cut lettuce is reported here.

Lettuce (Lactuca sativa L.) is an econorrically important food crop grown worldwide.

Demand far quality lettuce in the Australian domestic and export markets is high.

Visual quality of lettuce can be threatened by rots and browning, often leading to reduced shelf life and product quality issues with consumers.

We believe that the presence of plaM pathogenic bacteria may play a role in the elicitanon of the plant's defence mechanisms and be a major cause of browning at the cut surface.

Authors
Sue Pascoe
Robert Premier

Postharvest bacterial rots and browning in lettuce - 2002
Download 411kb

Conclusions:

This project has shown that fluorescent pseudomonads are capable of either causing a rapid browning reaction on the cut surface of lettuce or exacerbating the problem over a 48-hour period on bought lettuce or lettuce grown under sterile conditions.

The natural levels of fluorescent pseudomonads in soils of lettuce growing regions have been shown to vary over the seasons and also vary between crop types.

The finding that the after-harvest lettuce waste contained high populations of fluorescent pseudomonads resulted in a recommendation for a time lapse between harvest and replanting of seedlings.

Experiments conducted at Knoxfield have shown that different Pseudomonas species can induce browning of cut lettuce within 48 hours.

Browning is quite severe and rapid compared with other bacteria such as Erwima and Xanthomonas species.

The project has also shown that fluorescent pseudomonad levels on cut lettuce can be reduced, whilst maintaining good quality produce.

Also bacterial levels in the field were found to increase with the use of mulches, but the overall yield and quality of the lettuce heads were increased.

The results indicate that bacteria have an important role in not only rotting the cut surface of lettuce leaves but also in eliciting a browning response.

The cut surface of all leaves inoculated with bacteria turned brown whereas the cut surface of leaves that were not inoculated remained free of browning.

Recommendations :

  • Testing for fluorescent pseudomonads on the lettuce surface before processing to use as a warning system for lettuce that is likely to go brown.

  • Testing for fluorescent pseudomonads on lettuce as an indicator of the effectiveness of browning inhibition treatments, such as heat treatments, antimicrobial washes and chlorination.

  • Persistence of fluorescent pseudomonads on lettuce waste indicates that replanting should be conducted 10-14 days after the last harvest to reduce the chances of bacterial re-infection.

  • The use of plant based essential oils pre or post-harvest may be beneficial for the reduction of bacteria on the surface of fresh-cut lettuce (needs further research and development).

  • The use of mulches (of any type) are beneficial to lettuce production and increasing yields due to the soil water retention and the improved water infiltration in the field. They could provide large savings on water usage.

  • Maintenance of good postharvest conditions such as proper temperature management (<4�C) to improve the overall quality of lettuce and to retard growth of fluorescent pseudomonads.

Acknowledgments :

The completion of this project would have not have been possible without the assistance of a large number of people :

Kon Koroneos - Werribee South, Vic. Paul Gazzola - Somerville, Vic.
Nelson Cox - Lindenow, Vic. Bill Taylor Jnr - Boisdale, Vic.
John Faragher, Bruce Tomkins, James Hutchinson, Julia Behrsing and the other members of the NRE-IHD Food safety, quality and nutrition team

This project was commissioned by Horticulture Australia Limited�with funds frrom the Vegetable R&D levy and the Victorian State Government..

The Australian Government provides matched funding for all HAL's R&D activities.


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