Diseases and Pests: Bacterial Disease Management IAN TOTH, JAMES HUTTON INSTITUTE International Storage Conference Sponsored by Certis, 13 February 2014
What causes blackleg and soft rots? Bacteria belonging to the groups Pectobacterium and Dickeya cause blackleg in the field and soft rot in storage Pectobacterium atrosepticum (GB blackleg, soft rot) Pectobacterium carotovorum (GB soft rot) Dickeya dianthicola and D. solani (Europe blackleg and soft rot)
P. atrosepticum symptoms
Which pathogens are responsible for blackleg? Blackleg findings in seed potato stocks entered for classification in England and Wales (2010-2012). 2010 2011 2012 % seed stocks with blackleg 32.1 21.5 33.8 % blackleg caused by D. solani 7.0 2.3 1.8 % blackleg caused by D. dianthicola 0.4 0.6 1.8 % blackleg caused by P. atrosepticum 75.2 74.4 84.1 John Elphinstone (Fera)
Blackleg and seed production in Scotland Total area (%) with fault recorded at Growing Crop Inspection 2012 Rogues Groundkeepers Variations Leafroll Severe Mosaic Mild Mosaic Blackleg Maureen McCreath at SASA
Seed area downgraded or failed in Scotland 2000-2013 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Maureen McCreath at SASA
Crops with blackleg over tolerance Percentage crop area affected
Area (%) Area with blackleg recorded for each field generation (FG) 80 70 2011 2012 2013 60 50 40 30 20 10 0 FG 1 FG 2 FG 3 FG 4 FG 5 FG 6 Maureen McCreath at SASA
How are tubers contaminated? Contact with contaminated material, e.g. graders, machinery, boxes in storage, rotting tubers Within fields via infected potato plants, volunteers, alternative hosts, ground water, soil Between fields via insects, rain splash, aerosols Understanding contamination of high grade seed is crucial in delaying onset of blackleg
Control options Avoiding contamination Certification of seed potatoes including: Planting of pathogen-free minitubers Inspections and rogueing Grading of seed Diagnostic testing Effect of nutrition on plant resistance to blackleg and soft rot Calcium fertilizers Nitrogen fertilizers
Control options Breeding for resistance Traditional breeding no commercial cultivars are fully resistant (immune) But partial resistance is found in some cultivars Narrow range of genetic diversity in breeding material Good resistance found in CPC, incl. S. phureja (cultivated) and wild species Not highest priority compared to blight etc. Genetically modified (GM) potato plants
Control options Biological control Biocontrol bacteria Bacteriophages (commercial) Physical seed tuber treatment Hot water treatment Storage at low temp with ventilation
Storage Disease is caused by contaminated seed tubers - more contamination = more disease (weather dependant) Blackleg almost always occurs from contaminated seed Good storage conditions may prevent soft rot in storage but if bacteria are internal (lenticels, vascular tissue) storage is unlikely to lead to reductions in blackleg when seed is planted in the following season Good storage may reduce bacteria on tuber surface, including apical buds
Storage conditions Store in one-tonne boxes, in well-ventilated stores at low temperatures to avoid condensation on tuber surfaces and prevent multiplication of the pathogen. Wet tubers can lead to tuber decay and further spread of the bacteria when tubers are graded. Important to dry tubers rapidly by forced ventilation to remove field heat, remove moisture and dry up rots. Reduce holding temperature as soon as possible.
Guide to blackleg management
Seed and seed handling Best Practice for seed handling and storage
Scottish Government & Potato Council-Funded Blackleg Research (Pectobacterium spp.) How /when do early field generations become contaminated by Pectobacterium spp. (particularly P. atrosepticum - Pba) Use this information to modify current control strategies Delay infection in subsequent field generations Compare currently available haulm desiccants with sulphuric acid in their effect on spread of Pba.
Objectives Plant 25 Contamination of PB1 crops Movement within fields (Experimental) Pba movement through and between plants Determining populations of Pectobacterium Modelling the spread of Pectobacterium 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Drill A B C D E F G H I J K L M N O P Effectiveness of sulphuric acid treatment
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