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Bacterial Rots of Onion:Knowledge Gaps & the USDA SCRI Project
Lindsey du Toit, Washington State UniversityPacific Northwest Vegetable Association Annual Convention & Trade Show
20-21 November 2019, Kennewick, WA
Known bacterial pathogens of onion(Compendium of Onion & Garlic Diseases & Pests, 2nd Edition)
1. Bacillus cereus – soft rot2. Burkholderia cepacia (Pseudomonas cepacia) – sour skin3. Burkholderia gladioli pv. alliicola – slippery skin4. Dickeya chrysanthemi (Erwinia chrysanthemum) - soft rot5. Enterobacter cloacae – Enterobacter bulb decay6. Erwinia rhapontici – soft rot7. Eschericia sp. – soft rot8. Klebsiella sp. – soft rot9. Lactobacillus sp. – soft rot10. Pantoea agglomerans – bacterial leaf necrosis11. Pantoea ananatis – center rot12. Pantoea allii – center rot13. Pectobacterium carotovorum subsp. carotovorum - soft rot14. Pseudomonas aeruginosa – brown rot15. Pseudomonas marginalis pv. marginalis – soft rot16. Pseudomonas syringae – bacterial leaf spot17. Pseudomonas viridiflava – leaf streak/bulb rot18. Serratia marcescens – soft rot19. Xanthomonas axonopodis pv. allii – Xanthomonas leaf blight
Estimated $60 million in losses to bacterial diseases of onion annually in USA
Bacterial soft rots
Pantoea agglomerans, Pectobacterium carotovorum, Dickeya spp.
Bacterial leaf blights/dieback
Bacterial bulb rots
PNW: Burkholderia gladioli, Pantoea agglomerans, Enterobacter cloacae
Factors Favoring Onion Bacterial Diseases
Contaminated seed and transplants
Storm damage, rain, hail, frost damage
Mechanical wounds, insects (thrips), weeds
Irrigation - runoff, excess, overhead irrigation
Excessive fertility, especially post-bulb initiation
Moderate to high temperatures (>30oC), except for some Pseudomonas spp. (cool to warm)
Dense plant stands
Some topping, curing, and handling practices
Irrigation and bacterial bulb rotsTeviotdale et al. 1990. Effect of sprinkler vs. furrow irrigation on
incidence of bacterial bulb rot
Inoc. Inoc.No
inoc.
No
inoc.
Irrigation and bacterial bulb rots
Insects• Erwinia soft rot – onion maggot• Center rot/Pantoea leaf blight - thrips
Weeds• Pseudomonas leaf streak
cutleaf evening primrosedandelionpurple cudweed
• Pantoea leaf blight & center rotcommon cockle burcommon ragweedyellow nutsedge
Seed• Pantoea leaf blight (center rot)• Xanthomonas leaf blight
Factors Favoring Onion Bacterial DiseasesH.F. Schwartz
Management of bacterial diseases • Clean planting material – seed, transplants
• Sanitation - cull piles, volunteers
• Cultivar maturity, scouting, minimize wounding• Preventative sprays: No systemic bactericides
– coppers + EBDC (copper resistance?), disinfectants, Actigard- coverage, non-ionic surfactant, when to apply?
• Cultural practices:- Irrigation management: type, frequency, crop use (monitor soil moisture status), terminating irrigation- N-fertility: amount, final application ~bulb initiation, monitor crop nutrient status, avoid ‘bull necks’
• Curing:- Field curing: undercut bulbs, topping = wounding?- Postharvest curing: forced air, minimal heat
Post-harvest curingSchroeder, Humann, & du Toit. 2012. Plant Dis. 96:1548-1555.
Fig. 2. Burkholderia cepacia Fig. 3. Burkholderia gladioli
Evaluating Irrigation Management and ManKocidefor Internal Dry Scale and
Bacterial Bulb Rots of Onion – 2016 & 2017 trials
Lindsey du Toit and Tim Waters, Washington State UniversityOnion World May/June 2015, pp. 4-7
du Toit, L.J., Waters, T., and Reitz, S. 2016. Internal dry scale and associated bulb rots of onion. PNW 686. 8 pp.
2017 Results: Bulbs at harvestInternal dry scale, bacterial rot, black mold, & double centers
Factor Treatment
Dry scale
(0-3 severity
index)
Bacterial
rot (% of
bulbs)
Black
mold (%
of bulbs)
Double
centers (%
of bulbs)
Irrigation Wet 0.68 a 13.9 a 2.3 a 26.5 a
Dry 0.63 b 12.4 a 1.3 a 25.3 a
LSD 0.04 4.9 3.0 5.8
Inoculation Inoculated 0.67 a 21.0 a 2.2 a 22.8 b**
Non-inoculated 0.63 a 5.3 b 1.4 a 29.0 a
LSD 0.05 4.5 1.5 4.8
Bactericide ManKocide 0.67 a 12.5 a 1.8 a 26.3 a
No ManKocide 0.64 a 13.8 a 1.7 a 25.6 a
LSD 0.05 4.5 1.5 4.8
**Difficult to discern doubles on rotten onions
Evaluation of Foliar Applications of Bactericides for Management of Onion Bacterial Rot – 2019 trial
Lindsey du Toit, Tim Waters, Washington State UniversityBeth Gugino, Pennsylvania State University
IR-4 Minor Crops Program
No. Product Active ingredient Rate of applicationNo. of applic.
Application interval
1 Control - - - -
2 ManKocide Mancozeb + CuOH 2.25 lb/A 5 7 days
3 Kocide 3000-O CuOH 1.5 lb/A 5 7 days
4 Champ WG CuOH 1.5 lb/A 5 7 days
5 Oxidate 2.0 H2O2 + peroxyacetic acid 1.25 fl oz/2 ga 7 5 days
6 Kasumin 2L Kasugamycin 32 fl oz/A 4 7 days
7 Kasumin 2L 64 fl oz/A 4 7 days
8 Nano-MgO Nano-magnesium oxide 200 ug/ml 5 7 days
9 Nano-MgO 1,000 ug/ml 5 7 days
10 GWN 10120 Ammonia CuOH 2.0 pt/A 5 7 days
11 SP8010 Unknown 19 fl oz/A 5 7 days
12 SP8010 + Kocide3000-O
Unknown + CuOH 19 fl oz + 1.5 lb/A 5 7 days
13 SP8010 + SP2700 2% SP
Unknown 19 fl oz + 4.2 oz/A 5 7 days
14 Lifegard WG Bacillus mycoides J 4.5 oz/100 gal 5 7 days
15 Instill CuSO45H2O + metallic Cu 0.86 lb a.i./100 gal 3 7 days
• Planted Calibra on 1 April 2019 at 164,000 seed/A• Split-plot RCBD, 4 replications, bactericides to main plots, inoculation
treatments to split-plots = 120 plots• 15 bactericide treatment applications:
– Initiated on 24 July, at 5- to 7-day intervals, 3 to 5 times• Inoculated with B. gladioli and P. agglomerans on 1 & 15 August• Sprinklers turned on in late afternoon every other day for 15 min (Jul.-Aug.)• Rated plots weekly 6x for incidence & severity of bacterial blight (23 July - 27
August), & 2x for phytotoxicity (6 & 27 August)• Bulb yield (size & weight) measured on 7 Oct.• Bulb rot (incidence & severity) rated on 16 Oct.• Bulb rot in storage to be rated in Feb. 2020
2019 Foliar Bactericide Trial
Variable Inoculated Non-inoc. P value
8/20 disease incidence 37.7 ± 2.5% 7.5 ± 1.2% <0.0001
8/27 disease incidence 63.1 ± 3.3% 23.4 ± 2.2% <0.0001
8/20 disease severity (0-7) 4.3 ± 0.2 1.7 ± 0.2 <0.0001
8/27 disease severity (0-7) 5.7 ± 0.2 4.3 ± 0.2 <0.0001
Tops down on 8/06 55.1 ± 3.8% 47.8 ± 4.0% 0.0620
% bulbs with bacterial rot 50.9 ± 2.2% 35.0 ± 2.3% <0.0001
Mean bulb rot severity 16.7 ± 1.1% 8.5 ± 0.8% <0.0001
No. of marketable bulbs/plot 34.0 ± 1.2 37.2 ± 1.3 0.0205
Marketable bulb yield (t/A) 38.7 ± 1.3 45.8 ± 1.3 <0.0001
• B. gladioli & P. agglomerans inoculation caused leaf blight & bulb rot• Symptoms observed 19 days after inoculation• Inoculation affected all variables. Bactericide treatments only affected incidence of bulb rot
at harvest and marketable bulb yield (# of bulbs and tons/acre)• No interaction between inoculation treatments and bactericide treatments
Inci
de
nce
(%
) o
f b
ulb
s w
ith
bac
teri
al r
ot
Incidence (%) of bulb rotANOVA for bactericide = 0.0613ANOVA for bactericide*inoculation = 0.9792
* *
**
Incidence (%) of bulb rotANOVA P value for bactericide = 0.0613
** *
Marketable bulb yield (tons/acre)ANOVA P value for bactericide = 0.0263
2019 IR-4 Foliar Bactericide Trial• Inoculation + frequent overhead irrigation caused
severe bacterial leaf blight and bulb rot
• Bactericides were largely ineffective, except Kocide and Lifegard, despite 2 applications before inoculation
• Management of bacterial bulb rots requires effective pre-harvest cultural practices – irrigation & fertility
Stop the Rot: Combating onion bacterial diseases with pathogenomic tools & enhanced management
strategies
Southeast
11,200 A sweet
Bc Pag Pan
Pv Xaa
Columbia Basin
1,000 A sweet;
24,000 A storage
Bg Ec PagWSU
OSU
UCR
UI
USU CSU
NMSU
TAM
UGA
PSU
Cornell
MSU
Rockies
4,000 A storage
Bg Ec Pag
Pan Xaa
Treasure Valley
23,000 A storage
Bg Ec Pag
Midwest
2,500 A storage
Bc Pag PanNortheast
7,800 A storage
Bc Ec
Pag Pan
Southwest
31,200 A storage;
28,700 A non-storage
Bc Bg Ec Pag
du Toit et al. 2019. USDA NIFA SCRI Project No. 2019-51181-30013
Stop the RotUSDA NIFA SCRI Project No. 2019-51181-30013
• $4,044,300 + $4,200,000 matching (universities, stakeholders)
• 4 year-project: Oct. 2019-Sep. 2023• 24 collaborators
• PD = Lindsey du Toit, WSU• Co-PI’s = Bhabesh Dutta & Brian Kvitko, Univ. of Georgia;
Christy Hoepting, Cornell Extension; Brenna Aergerter, Univ. of California; Mark Uchanski, Colorado State Univ.
• 12 states + Teresa Coutinho, Univ. of Pretoria, South Africa
• 12-member Stakeholder Advisory Panel• Kerrick Bauman, Michael Locati represent PNW
Stop the RotUSDA NIFA SCRI Project No. 2019-51181-30013
• Objective A: Onion bacterial disease characterization• A1 – Survey onion crops nationally for bacterial pathogens• A2 – Genetic analyses, virulence factors, bacterial communities• A3 – Develop molecular diagnostic tools• A4 – Develop methods to screen for resistance to bacterial
diseases of onion
• Objective B: Onion bacterial disease management• B1 – Irrigation practices• B2 – Fertility practices• B3 – Pesticide programs• B4 – Cultural practices• B5 – Postharvest practices• B6 – Bacterial disease modeling/risk prediction• B7 – Economic assessments, Extension/outreach
Stop the RotUSDA NIFA SCRI Project No. 2019-51181-30013
Washington State University team members:• Lindsey du Toit, Plant Pathologist• Tim Waters, Extension Specialist & Entomologist• Gabriel LaHue, Soil Scientist• Kirti Rajagopalan, Computer Scientist• Ananth Kalyanamaran, Data Modeler• Heather MacKay, Project Manager• Graduate students & technical staff
• Onion bacterial samples, fields surveyed• Field trial participation• Economic assessment of bacterial issues/needs• Bacterial disease risk modeling/prediction• Feedback on project direction, progress, etc.
Acknowledgements
Play With Your Food
• USDA NIFA SCRI• Pacific Northwest Vegetable Association• Columbia Basin Onion Research
Committee• WSCPR• IR-4 Minor Crops Program• Onion growers, consultants, seed
companies
WSU: Tim WatersDon Kinion, Jennifer Darner, Erika Ramirez Garcia, Eduardo Sallas, Andrea Vallejo Gutierrez
Mike Derie, Barbara Holmes, Paul Morgan, Erin Miller, Haruka Fukada, Ryan Solemslie