elisabeth wood defense seminar final
TRANSCRIPT
The use of volatile organic compounds to control postharvest
potato pathogens
Elisabeth M. Wood
Aberdeen Research and Extension CenterDepartment of Plant, Soil and Entomological Sciences
University of Idaho
Major Professor: Dr. Phillip Wharton
Agenda Introduction
Potato Storage Diseases Volatile Compounds
Objectives Will plant derived volatile organic compounds work to control
postharvest potato pathogens?
Results in vitro studies Mode of action studies in vivo studies
Conclusions
Introduction
Potatoes are a food source for millions of people
Can be processed and utilized in a variety of ways making them a highly desirable crop
Able to be stored for many months after harvest
Time spent in storage can lead to loss from disease
Controlled by carefully monitoring storage temperature, humidity, and sanitation
Spread easily and quickly through storage, especially if potatoes are damaged during harvest
In storage, one of the only defense mechanisms available to potatoes is their impermeable skin
Only a few fungicides approved for direct use on edible product
Expensive control measures and losses from disease can be costly to producers
There is a need for better disease control methods
Potato Storage Diseases
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Blemish diseases of
potatoes caused by 3 main
pathogens:
P. atrosepticum is the causal agent of potato soft rot and pit rot
Infected in wet soils (anaerobic conditions), high humidity and warm temperatures in field and storage
The bacterium contains pectolytic enzymes
• Pectobacterium atrosepticum
• Colletotrichum coccodes• Helminthosporium solani
Blemish diseases of
potatoes caused by 3 main
pathogens:
C. coccodes is the causal agent of blackdot
Symptoms on stems and roots, and senesce prematurely (early die off)
Infected tubers have sooty lesions (microsclerotia)
Does not spread in storage
• Pectobacterium atrosepticum
• Colletotrichum coccodes
• Helminthosporium solani
Blemish diseases of
potatoes caused by 3 main
pathogens:
H. solani is the causal agent of silver scurf
Infected by soil-borne inoculum
Storage spread via air-borne conidia
Infected potatoes show silvery raised lesions and rough skin
• Pectobacterium atrosepticum
• Colletotrichum coccodes
• Helminthosporium solani
Storage rots of potatoes caused
by 3 main pathogens:
P. erythroseptica is the causal agent of pink rot
Stolons infected in water-saturated soils. In storage, infection spreads in warm and humid conditions via zoospores.
Softened tuber tissue turns pink when exposed to air
• Phytophthora erythroseptica
• Pythium ultimum• Phytophthora infestans
Storage rots of potatoes caused
by 3 main pathogens:
P. ultimum is the causal agent of pythium leak
Infected during harvest through wounds when humidity and temperatures are high
Infected potatoes have soft, discolored tuber tissue and watery discharge
• Phytophthora erythroseptica
• Pythium ultimum• Phytophthora infestans
Storage rots of potatoes caused
by 3 main pathogens:
P. infestans is the causal agent of late blight
Infected by plant material or soil, high humidity and warm temperatures in field and storage. Infection can spread quickly in storage
Infected potatoes show rust colored tissue and darkened lenticels
• Phytophthora erythroseptica• Pythium ultimum
• Phytophthora infestans
Other potato diseases, 3 more
pathogens:
F. sambucinum is a causal agent of dry rot
Infected by soil-borne inoculum, in storage spreads quickly and is able to infiltrate wounded skin
Infected potatoes have visible mycelia in tuber wounds
Dry rot infection is often followed by soft rot infection (P. atrosepticum)
• Fusarium sambucinum
• Alternaria solani• Sclerotinia sclerotiorum
A. solani is the causal agent of potato early blight
Infected when tuber skin is wounded during harvest
Typically a foliar pathogen, but infected potatoes have sunken, corky, lesions that extend into tuber tissue
• Fusarium sambucinum
• Alternaria solani• Sclerotinia sclerotiorum
Other potato diseases, 3 more
pathogens:
S. sclerotiorum is the causal agent of white mold
Potato stems and leaves infected in the field at flowering, kills stems and can cause early senesce
Not typically a tuber pathogen in the USA, but has been shown to infect tubers under specific conditions resulting in tuber tissue decay
• Fusarium sambucinum• Alternaria solani
• Sclerotinia sclerotiorum
Other potato diseases, 3 more
pathogens:
Infected potato images courtesy of Queensland Government Department of Agriculture, Fisheries, and Forestry
Agenda Introduction
Potato Storage Diseases Volatile Compounds
Objectives Will plant derived volatile organic compounds work to control
postharvest potato diseases?
Results in vitro studies Mode of action studies in vivo studies
Conclusions
2E-hexenal is a naturally produced volatile compound (lipoxygenase pathway)
Previous studies show anti-fungal and anti-bacterial properties
Approved by the FDA as a food/flavor additive
Volatile nature allows for highly effective control methods such as fumigation or headspace treatment
2E-hexenal
Volatile compounds to control disease
H 3C
Acetaldehyde is a naturally produced volatile compound (pyruvic acid and pyruvate decarboxylase)
Previous studies show slowing of the ripening process of fruit
Previous studies show anti-fungal properties
Volatile nature allows for highly effective control methods such as fumigation or headspace treatment
Volatile compounds to control disease
Acetaldehyde
Agenda Introduction
Potato Storage Diseases Volatile Compounds
Objectives Will plant derived volatile organic compounds work to control
postharvest potato diseases?
Results in vitro studies Mode of action studies in vivo studies
Conclusions
Objectives
Which volatile compound is the most effective and at what concentration in vitro?
Can this volatile compound control other potato pathogens in vitro?
What is the mode of action of this volatile compound?
Can this volatile compound control these pathogens in vivo?
In vitro methods
Results: Acetaldehyde least effective
Acetaldehyde Did not inhibit the growth of
any of the blemish pathogens
None of the treatment volumes of acetaldehyde were significantly different from the untreated control
Results: P. atrosepticum2.5 µL/L of 2E-hexenal was capable of inhibiting growth of P. atrosepticum completely in vitro.
() UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
2.5 µL/L
Untreated Control
Results: C. coccodes2.5 µL/L of 2E-hexenal was capable of slowing C. coccodes growth, but 5 µL/L completely inhibited growth in vitro.
Untreated Control
() UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
2.5 µL/L5 µL/L
Results: H. solani2.5 µL/L of 2E-hexenal was able to inhibit the growth of H. solani completely in vitro.
2.5 µL/L
Untreated Control
() UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
Objectives
Which volatile compound is the most effective and at what concentration in vitro? 2E-hexenal at 5 µL/L for potato blemish
pathogens
Which volatile compound is the most effective and at what concentration in vitro? 2E-hexenal at 5 µL/L for potato blemish pathogens
Can this volatile compound control other potato pathogens in vitro?
What is the mode of action of this volatile compound?
Can this volatile compound control these pathogens in vivo?
Results: P. erythroseptica2.5 µL/L was capable of slowing P. erythroseptica growth, 5 µL/L capable of inhibiting growth completely in vitro.
Untreated Control
() UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
Dia
met
er in
mm
2.5 µL/L5 µL/L
Results: P. ultimum2.5 µL/L was capable of capable of inhibiting P. ultimum growth completely in vitro.
2.5 µL/L
Untreated Control
() UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
Dia
met
er in
mm
Results: P. infestans2.5 µL/L was capable of capable of inhibiting P. infestans growth completely in vitro.
2.5 µL/L
Untreated Control
() UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
Dia
met
er in
mm
Results: F. sambucinum7.5 µL/L was capable of inhibiting F. sambucinum growth completely in vitro, with 2.5 and 5 µL/L able to slow the growth of the pathogen in vitro.
() UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
Dia
met
er in
mm
Untreated Control
2.5 µL/L5 µL/L7.5 µL/L
Results: A. solani5 µL/L was capable of capable of inhibiting A. solani growth completely in vitro, although 2.5 µL/L did slow the growth of the pathogen in vitro.
Untreated Control
() UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
Dia
met
er in
mm
2.5 µL/L5 µL/L
Results: S. sclerotiorum2.5 µL/L was capable of inhibiting S. sclerotiorum growth completely in vitro.
2.5 µL/L
Untreated Control
() UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
Dia
met
er in
mm
Objectives
Can this volatile compound control other potato pathogens in vitro? 7.5 µL/L 2E-hexenal toxic to all tested
pathogens in vitro
Which volatile compound is the most effective and at what concentration in vitro? 2E-hexenal at 5 µL/L for potato blemish pathogens
Can this volatile compound control other potato pathogens in vitro? 7.5 µL/L 2E-hexenal toxic to all tested pathogens in
vitro
What is the mode of action of this volatile compound?
Can this volatile compound control these pathogens in vivo?
Blemish pathogen C. coccodes and H. solani Microscopy experiments were
completed to understand the relationship between 2E-hexenal and the two fungal blemish pathogens Germination rate Hyphal elongation
C. coccodes germination in vitro2.5 µL/L capable of completely inhibiting C. coccodes conidial germination in vitro.
2.5 µL/L
Untreated Control
C. coccodes hyphal elongation in vitro2.5 µL/L 2E-hexenal capable of significantly decreasing hyphal elongation of C. coccodes in vitro.
2.5 µL/L
Untreated Control
H. Solani germination in vitro2.5 µL/L capable of strongly inhibiting conidial germination in vitro. H. solani has a notably slower rate of germination than C. coccodes.
2.5 µL/L
Untreated Control
H. Solani hyphal elongation in vitro2.5 µL/L 2E-hexenal capable of somewhat decreasing hyphal elongation of H. solani in vitro. However, with low germination rates and very slow rates of growth the results are more modest.
2.5 µL/L
Untreated Control
Results: Mode of Action
C. coccodes Blackdot
H. solani Silver Scurf
C. acutatum untreated cell
C. acutatum : 2E-hexenal
Arroyo, F. T., Moreno, J., Daza, P., Boianova, L., and Romero, F., 2007. Antifungal activity of strawberry fruit volatile compounds against Colletotrichum acutatum. Journal of Agricultural and Food Chemistry. 55:5701–5707
2E-hexenal inhibits C. coccodes and H. solani conidial germination and significantly reduces hyphal elongation
Other research has shown that 2E-hexenal scrambles cellular membranes disrupting organelles and important cellular functions
C. acutatum untreated cell
C. acutatum : 2E-hexenal
Objectives
What is the mode of action of this volatile compound? 2E-hexenal inhibited conidial germination
as well as hyphal elongation in the blemish pathogens C. coccodes and H. solani
Which volatile compound is the most effective and at what concentration in vitro? 2E-hexenal at 5 µL/L for potato blemish pathogens
Can this volatile compound control other potato pathogens in vitro? 7.5 µL/L 2E-hexenal toxic to all tested pathogens in vitro
What is the mode of action of this volatile compound? 2E-hexenal inhibits conidial germination as well as hyphal
elongation in the blemish pathogens C. coccodes and H. solani
Can this volatile compound control these pathogens in vivo?
In vivo methodsLarge Scale Trials(C. Coccodes)
Small Scale Trials
Molecular and Visual Quantification
Results: C. coccodes large-scale trialUnder large-scale experimental conditions, 2E-hexenal did not inhibit the growth of C. coccodes over 5 months in storage.The amount of C. coccodes present on naturally infected potatoes increased over time in storage on the untreated control.
Results: in vivo large-scale trial
Results indicate that 2E-hexenal was not effective in controlling C. coccodes in vivo, why?
Small-scale trials designed to over come these possible issues
Poor circulation of 2E-hexenal
Respiring potatoes may interact with 2E-hexenal and decrease concentration
Broad sample collection times
C. coccodes does not spread in storage, symptoms worsen
Improvements
In vivo methodsSmall Scale Trials
Potatoes treated with 2E-hexenal absorbed the volatile compound for up to 5 days after treatment
Molecular and Visual Quantification
Both the tuber peel (2 mm) and tuber tissue absorbed 2E-hexenal, absorption was independent of treatment volume and tuber surface area
Un-inoculated Tubers
Results: C. coccodes small scaleUnder small-scale experimental conditions, 2E-hexenal did not inhibit the growth of C. coccodes In vivo.
Untreated Control
50 µL/L
Results: P. atrosepticum small-scale trialUnder small-scale experimental conditions, 2E-hexenal did not inhibit the growth of P. atrosepticum in vivo, and in fact may have increased disease severity due to anaerobic conditions.
All replications
Bacterial Soft Rot SymptomsBacterial Pit Rot Symptoms
50 µL/L
Untreated Control
Results: P. erythrosepticaUnder small-scale experimental conditions, 2E-hexenal did not inhibit the growth of P. erythroseptica in vivo.
All replications
Untreated Control
50 µL/L
Results: P. ultimumUnder experimental conditions, 2E-hexenal did not inhibit the growth of P. ultimum in vivo.
Untreated Control
50 µL/L
Results: H. solaniUnder experimental conditions, 2E-hexenal inhibited the growth of H. solani in vivo at the minimum treatment volume of 5 µL/L.
50 µL/L
Untreated Control
Results: in vivo small-scale trial
Results indicate that 2E-hexenal controlled H. solani in vivo but nothing else, why?
Decrease treatment volumes
Decrease treatment time
Increase oxygen presence and volatile circulation
Treat prior to inoculation
Low oxygen conditions (P. atrosepticum) due to increased treatment concentrations
Anoxic conditions lower potato defense mechanisms
Rot pathogens penetrate tuber tissue deeper than volatile
C. coccodes microsclerotia
H. solani rapid sporulation on tuber surface
Improvements
Objectives
Can this volatile compound control these pathogens in vivo? 2E-hexenal inhibited H. solani in vivo at 5
µL/L
Which volatile compound is the most effective and at what concentration in vitro? 2E-hexenal at 5 µL/L for potato blemish pathogens
Can this volatile compound control other potato pathogens in vitro? 7.5 µL/L 2E-hexenal toxic to all tested pathogens in vitro
What is the mode of action of this volatile compound? 2E-hexenal inhibits conidial germination as well as hyphal
elongation in the blemish pathogens C. coccodes and H. solani
Can this volatile compound control these pathogens in vivo? 2E-hexenal inhibited H. solani in vivo at 5 µL/L
Agenda Introduction
Potato Storage Diseases Volatile Compounds
Objectives Will plant derived volatile organic compounds work to control
postharvest potato diseases?
Results in vitro studies Mode of action studies in vivo studies
Conclusions
Overall Conclusions: Acetaldehyde was not effective
2E-hexenal was effective
7.5 µL/L of 2E-hexenal inhibited growth of all tested pathogens in vitro
Mode of action: inhibition of conidial germination and prevention of hyphal elongation in fungal blemish pathogens at 2.5 µL/L
This shows promise for in vivo control, but more to work is needed for commercialization
Applications:
Low treatment volumes
Fumigation
Active packaging
Further research Improved In vivo studies Inclusion complexes and
polymeric plastic films (packaging)
With further research, 2E-hexenal could be used to
control the growth of postharvest potato pathogens,
and an alternative to postharvest fungicides.
Almenar, E., Auras, R., Wharton, P., Rubino, M., & Harte, B. (2007). Release of acetaldehyde from β-cyclodextrins inhibits postharvest decay fungi in vitro. Journal of Agricultural and Food Chemistry, 55, 7205–7212.
Acknowledgements:
Thank you for your time.
Committee:Phillip WhartonNora OlsenJoe KuhlRafael Auras
Potato Pathology Crew:Tim MilesLaura MilesKatie FairchildDarrah Ricard
Equipment Support:Joe KuhlPamela HutchinsonLouise-Marie Dandurand
Questions?
Thank you for your time