Management of

blackleg caused by

Dickeya

Amy Charkowski

Professor

BioAgricultural Sciences and Pest Management

Collaborators: Jay Hao Gary Secor Keith Perry Carol Ishimaru Steve Johnson Noah Rosenzweig Funding:

Grower Organizations Universities USDA-ARS USDA-CARE

Advisors: Gerry Saddler* Ian Toth Jean van der Wolf Minna Pirhonen

Closely related bacterial pathogens Cause rot, wilt, and blackleg in many crops, including potato Dickeya is an emerging problem in potato in some regions

Dickeya and Pectobacterium

Field Symptoms - Dickeya

Multiple blackleg species are present in North American potatoes Pectobacterium atrosepticum P. carotovorum subsp. carotovorum P. carotovorum subsp. brasiliense P. carotovorum subsp. odoriferum P. parmentieri (P. wasabiae) Dickeya dianthicola D. dadantii

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

Wikipedia

Because multiple species are present and they infect many plant species, there are significant challenges in: -Detection -Epidemiology -Breeding for resistance

What caused this outbreak?

Rain in 2013 and 2014 spread pathogen, but cool temperatures caused latency. Warmer temps in 2015 on commercial farms resulted in significant outbreak.

Can we eliminate Dickeya?

Is it a recent introduction? Is it established in the environment?

Pathogen Potato

Blackleg disease diagram and management

Farm Environment

Pathogen Potato

Pathogen testing, sanitation

Blackleg disease diagram and management

Farm Environment

Is seed lot testing available for Dickeya?

1. Which test to use? 2. Which part of plant to test? 3. How many samples to test

per seed lot? 4. When to test the plants? 5. Are tests predictive of disease

the next year?

There is no inexpensive single test that can identify all Pectobacterium and Dickeya species

In 2015-2016, tested all published PCR assays for Dickeya and Pectobacterium PelADE and Dia-C PCR assays were effect and are currently the most commonly used

PelADE = detects all Dickeya species Dia-C = detects D. dianthicola Additional assays in final stages of development

Recent lab validation assays with 7 different labs led by Secor (NDSU) and Fox (Maine) 98% agreement between labs

Which part of potato plant should be tested for

Dickeya?

How many tubers should be tested per seed lot?

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Probability of infected seed tuber in lot

When to test for Dickeya?

Field Season: up to 5 stems per field when symptoms present (WI) Post-Harvest: 454 lots of 1058 total (ME) 150 lots from 16 states, 3 provinces (ND) FY1-FY3 lots (WI)

Should stems from a post-harvest grow-out be tested for Dickeya?

Dickeya is endemic in Hawaii and Florida. Cross-contamination can occur during shipping and planting. Symptoms may not develop reliably. Recommendation: If symptoms occur in the post-harvest test, have a second sample from the warehouse tested for Dickeya.

Are lab tests on tubers predictive of disease the following year?

Very little data available for the US Symptoms seem more likely to occur on East Coast Hot and humid weather promotes disease

In Netherlands: Samples tested in 4 groups of 50 tubers, with minimum of 200 per seed lot All samples negative = 3-4% chance of blackleg in the subsequent year. 1 to 3 positive = ~10% of lots have blackleg 4 positive = ~25% of lots have blackleg If Dickeya is present, expect blackleg in ~50% of seed lots If multiple Dickeya/Pectobacterium strains are found, then rate of blackleg is very high.

Already routinely tested Dickeya quickly kills plantlets in tissue culture

Are tissue culture plantlets a source of Dickeya?

Are greenhouse-grown tubers a source of

Dickeya?

Epidemiological evidence so far does not support this. Severe symptoms likely to develop under greenhouse conditions.

Are greenhouse-grown tubers a source of Dickeya?

To reduce risk in a greenhouse: 1. Irrigate with high quality water (ground water, not surface water). 2. Use good sanitation protocols. 3. Do not grow other crops alongside seed potatoes in greenhouses.

Sanitizers for blackleg management

Dickeya and Pectobacterium are very sensitive to sanitizers

Follow label directions, sanitize between seed lots at planting and harvest.

Same sanitizers also control spread of viruses and fungi

http://www.uap.ca/products/documents/COPPERFUNGICIDESAUG2010.pdf

Senator PSPT or Senator 509C (Thiophanate-methyl) as a seed piece treatment for Pectobacterium atrosepticum (blackleg)

-use on clean surfaces -use recommended dilution -leave wet for 10 minutes -rinse with potable water afterward and air dry

New Brunswick

Ontario

Pathogen Potato

Pathogen spread

Blackleg disease diagram and management

Farm Environment

How does Dickeya spread?

1. Seed 2. Irrigation water 3. Insects (spread Pectobacterium) 4. Equipment

Survival in soil is not an important factor

Are weeds or volunteer potatoes important for

spread of Dickeya?

Little data available for US fields Possible risk for seed growers Unlikely to be a major risk for commercial growers

Pathogen Potato

Potato resistance

Blackleg disease diagram and management

Farm Environment

Are there resistant varieties?

Potato varieties differ in susceptibility.

Little is known about mechanisms of resistance/tolerance and good molecular markers are lacking

Pathogen Potato

Questions?

Farm Environment