Dickeya - University of Wisconsin–Madison

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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
-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
Management challenges for Dickeya and
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
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
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
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
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.
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
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
Irrigation water can be tested for
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.
Thank you!