Transcript Dickeya - University of Wisconsin–Madison
Biology and Management of Bacterial Soft Rot Amy Charkowski University of Wisconsin-Madison North American Dickeya Outbreak In 2015, Dickeya caused significant losses in potato, mainly in the Eastern US. Dickeya and Pectobacterium are closely related bacterial pathogens Erwinia carotovora = Pectobacterium Erwinia chrysanthemi = Dickeya Seed piece decay, blackleg, stem rot, tuber soft rot Dickeya and Pectobacterium live in xylem. They cause symptoms by digesting plant cell walls. Dickeya dianthicola caused the 2015 outbreak Dickeya dianthicola -Found in US and worldwide -Possibly present in US in other crops for many years Dickeya solani -Aggressive soft rot species -Emerged in Netherlands -Not yet reported in North America Dickeya and Pectobacterium infect many plant species Dickeya and Pectobacterium don’t appear to thrive on legumes or small grains Where would Dickeya and Pectobacterium likely be found on a farm? What caused the 2015 Dickeya outbreak? Dickeya had probably been present in seed for at least a few years. Rain in 2013 and 2014 spread pathogen, but cool temperatures caused latency. Warmer temps in 2015 on commercial farms resulted in significant outbreak. We can recover from this outbreak Good PCR tests for Dickeya are available. -Identify seed lots with a high incidence of Dickeya and remove these from the seed system. -Survey seed lots to avoid another outbreak. Seed potatoes can be tested for Dickeya PCR assays for Dickeya and Pectobacterium are available. Test extracts from stem end of tuber, as with Clavibacter. Multiplexing Clavibacter and Dickeya assays is feasible, and is being validated now. Testing for Dickeya Potato stem-end core extract that tested positive for Dickeya. Probability of erroneous acceptance of field How many tubers should be tested per seed lot for Dickeya? Clayton and Slack. 1988. Amer. Potato J. Probability of infected seed tuber in lot How many tubers should be tested per seed lot for Dickeya? 400 tubers per lot = likely to identify seed lots with 1% or greater incidence. 1200 tubers per lot = likely to identify seed lots with 0.3% or greater incidence. Multiple species of Dickeya and Pectobacterium can be present in same seed lot If you see symptoms and want to know if Dickeya is present, send multiple samples. -random sample of healthy appearing tubers/stems -”least diseased” symptomatic tubers/stem Management challenges for Dickeya and Pectobacterium No curative chemicals Resistant varieties not available Little ability to predict when disease will be severe in fields Management at Planting Purchase and plant only certified seed potatoes. - limited generation seed with tags - without blackleg noted on health certificate Dickeya and Seed Certification What should certification threshold be for Dickeya? Should blackleg incidence be reported on health certificates? What could certification agencies do right now? Did a small survey of Wisconsin FY-3 seed potatoes 30 tubers per lot 165 lots total No Dickeya was found. Pectobacterium was isolated from one lot. Recorded blackleg & stem rot in postharvest test. Follow-up on any lots where blackleg or stem rot is seen. Management at Planting Cutting seed will spreads Pectobacterium and Dickeya within a seed lot. Management at Planting When possible, plant uncut seed. Thoroughly sanitize seed cutting equipment and planter between seed lots. Management at Planting Warm the seed prior to planting so that it is approximately the same temperature as the soil (50OF) Reduces water condensation on tubers. Dickeya can not digest tuber periderm If cutting seed, suberize it prior to planting to avoid new infections. Problems at Planting When Dickeya is in seed: -poor stands -late emergence -weak plants Problems at Planting If you have a field like this – Test for Dickeya Try not to spread bacteria to other seed fields on equipment. Make backup plans since this field may be unharvestable. Dickeya and Pectobacterium thrive in water and low oxygen Over-irrigation or excessive rain will spread Dickeya and Pectobacterium. If possible, prepare field to avoid excessive water in field. Management of Blackleg Blackleg = bacterial pathogen in tuber kills base of potato stem Management of Blackleg Dickeya and Pectobacterium can both cause blackleg Only management option is copper sprays to try to reduce spread of bacteria to healthy plants. Dickeya “slow wilt” Dickeya can cause potatoes to wilt at any point in the growing season. Dickeya “slow wilt” Copper sprays can slow spread of disease in field, but it is not curative. Copper sprays also interfere with detection assays and copper can build up in soil. Dickeya does not survive well in soil Dickeya is not a good soil survivor (generally less than 2 years) and rotation out of potato for at least 3 years will greatly reduce disease. It survives well in surface water and weed roots. Dickeya and Pectobacterium can spread after severe storms Plant nutrition affects susceptibility Calcium helps protect against soft rot bacteria Too much nitrogen makes plants more susceptible to soft rot bacteria. Management at Harvest Potato tuber condition never improves during harvest or in storage. Soft rot pathogens will take advantage of any errors in harvesting or storing potatoes. Management at Harvest If soft rot is present in a portion of the field, do not harvest this part of the field. Sanitize harvest equipment between lots. Management at Harvest Dickeya grows slowly or not at all at seed storage temperatures, so if crop looks good going into storage, it will likely not decay in storage due to Dickeya. But, the bacteria will likely cause disease and spread the next year if these potatoes are planted. Management at Harvest Dickeya may leave a farmer with nothing to harvest. or Tubers may store well, even if infected with Dickeya. May depend on temperature during growing season. Can Dickeya infect tissue culture plantlets? Tissue culture plants are unlikely to survive if infected with Dickeya. Tissue culture testing for soft rot pathogens is already routine. Can Dickeya infect tissue culture plantlets or plants in greenhouses? Dickeya could feasibly spread in a greenhouse in NFT or potting-soil based systems. Irrigation water can be tested for Dickeya. Summary Blackleg incidence might not be recorded separately on seed potato health certificates. Testing is available for Dickeya and Pectobacterium. Disease thresholds for Dickeya are not yet determined. Management for Dickeya and Pectobacterium is the same and these management practices will also reduce incidence of many other potato diseases. http://labs.russell.wisc.edu/potato-blackleg/ Thank you!