1. 
Elisabeth M. Wood
Aberdeen Research and Extension Center
Department of Plant, Soil and Entomological Sciences
University of Idaho
Major Professor: Dr. Phillip Wharton

2. 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

3. 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

4. Potato Storage Diseases
 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

5. Blemish diseases of  P. atrosepticum is the causal
agent of potato soft rot and
potatoes caused by 3 pit rot
main pathogens:  Infected in wet soils
• Pectobacterium (anaerobic conditions), high
humidity and warm
atrosepticum temperatures in field and
• Colletotrichum coccodes storage
• Helminthosporium solani  The bacterium contains
pectolytic enzymes

6.  C. coccodes is the causal
Blemish diseases of agent of blackdot
potatoes caused by 3  Symptoms on stems and
main pathogens: roots, and senesce
prematurely (early die off)
• Pectobacterium
atrosepticum  Infected tubers have sooty
lesions (microsclerotia)
• Colletotrichum
coccodes  Does not spread in storage
• Helminthosporium solani

7. Blemish diseases of  H. solani is the causal agent of
silver scurf
potatoes caused by 3
 Infected by soil-borne
main pathogens: inoculum
• Pectobacterium
atrosepticum  Storage spread via air-borne
conidia
• Colletotrichum coccodes
 Infected potatoes show
• Helminthosporium
silvery raised lesions and
solani rough skin

8.  P. erythroseptica is the causal
Storage rots of agent of pink rot
potatoes caused by 3  Stolons infected in water-
saturated soils. In storage,
main pathogens: infection spreads in warm and
• Phytophthora humid conditions via
zoospores.
erythroseptica
• Pythium ultimum  Softened tuber tissue turns
pink when exposed to air
• Phytophthora infestans

9.  P. ultimum is the causal agent
Storage rots of of pythium leak
potatoes caused by 3  Infected during harvest
main pathogens: through wounds when
humidity and temperatures
• Phytophthora erythroseptica
are high
• Pythium ultimum
 Infected potatoes have soft,
• Phytophthora infestans discolored tuber tissue and
watery discharge

10.  P. infestans is the causal agent
of late blight
Storage rots of
potatoes caused by 3  Infected by plant material or
soil, high humidity and warm
main pathogens: temperatures in field and
storage. Infection can spread
• Phytophthora erythroseptica
quickly in storage
• Pythium ultimum
 Infected potatoes show rust
• Phytophthora colored tissue and darkened
infestans lenticels

11.  F. sambucinum is a causal
Other potato diseases, agent of dry rot
3 more pathogens:  Infected by soil-borne
• Fusarium inoculum, in storage spreads
quickly and is able to infiltrate
sambucinum wounded skin
• Alternaria solani
 Infected potatoes have visible
• Sclerotinia sclerotiorum
mycelia in tuber wounds
 Dry rot infection is often
followed by soft rot infection
(P. atrosepticum)

12.  A. solani is the causal agent of
Other potato diseases, potato early blight
3 more pathogens:  Infected when tuber skin is
• Fusarium sambucinum wounded during harvest
• Alternaria solani  Typically a foliar pathogen,
• Sclerotinia sclerotiorum but infected potatoes have
sunken, corky, lesions that
extend into tuber tissue

13.  S. sclerotiorum is the causal
Other potato diseases, agent of white mold
3 more pathogens:  Potato stems and leaves
• Fusarium sambucinum infected in the field at
• Alternaria solani flowering, kills stems and can
cause early senesce
• Sclerotinia
 Not typically a tuber
sclerotiorum pathogen in the USA, but has
been shown to infect tubers
under specific conditions
resulting in tuber tissue decay
Infected potato images courtesy of Queensland Government Department of
Agriculture, Fisheries, and Forestry

14. 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

15. Volatile compounds to
control disease
 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
2E-hexenal additive
 Volatile nature allows for highly
effective control methods such as
C fumigation or headspace treatment
H3

16. Volatile compounds to
control disease
 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
Acetaldehyde properties
 Volatile nature allows for highly
effective control methods such as
fumigation or headspace treatment

17. 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

18. 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?

19. In vitro methods

20. Results: Acetaldehyde least effective
Acetaldehyde
 Did not inhibit the growth of  None of the treatment
any of the blemish volumes of acetaldehyde
pathogens were significantly different
from the untreated control

21. () UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
2.5 µL/L
Results: P. atrosepticum
2.5 µL/L of 2E-hexenal was capable of inhibiting growth of P. atrosepticum
completely in vitro.
Untreated Control

22. () UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
2.5µL/L
5 µL/L
Results: C. coccodes
2.5 µL/L of 2E-hexenal was capable of slowing C. coccodes growth, but 5
µL/L completely inhibited growth in vitro.
Untreated Control

23. () UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
2.5 µL/L
Results: H. solani
2.5 µL/L of 2E-hexenal was able to inhibit the growth of H. solani
completely in vitro.
Untreated Control

24. Objectives
 Which volatile compound is the most effective and at
 Which volatile compound is the most
what concentration in vitro?
effective and at µL/L forconcentration in vitro?
 2E-hexenal at 5 what potato blemish pathogens
 2E-hexenal at 5 µL/L for potato blemish
 Can this volatile compound control other
pathogens
potato pathogens in vitro?
 What is the mode of action of this volatile compound?
 Can this volatile compound control these pathogens in
vivo?

25. () UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
P. erythroseptica in vivo
60
50
40
Diameter in mm
Diameter (mm)
30
20
2.5µL/L
5 µL/L 10
0
-10
0 1 2 3 4 7 8
Days Post Inoculation
Results: P. erythroseptica
2.5 µL/L was capable of slowing P. erythroseptica growth, 5 µL/L capable of
inhibiting growth completely in vitro.
Untreated Control

26. () UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
P. ultimum in vitro
60
50
40
Diameter in mm
Diameter (mm)
30
20
2.5 µL/L 10
0
-10
0 1 2 3 4 7 8
Days Post Inoculation
Results: P. ultimum
2.5 µL/L was capable of capable of inhibiting P. ultimum growth completely
in vitro.
Untreated Control

27. () UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
P. infestans in vitro
60
50
40
Diameter in mm
Diameter (mm)
30
20
2.5 µL/L 10
0
-10
0 1 2 3 4 7 8
Days Post Inoculation
Results: P. infestans
2.5 µL/L was capable of capable of inhibiting P. infestans growth
completely in vitro.
Untreated Control

28. () UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
F. sambucinum in vitro
60
50
40
Diameter in mm
Diameter (mm)
30
20
2.5µL/L
7.5 µL/L
5 10
0
-10
0 1 2 3 4 7 8
Days Post Inoculation
Results: F. sambucinum
7.5 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.
Untreated Control

29. () UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
A. solani in vitro
60
50
40
Diameter in mm
Diameter (mm)
30
20
2.5 µL/L
5 µL/L 10
0
-10
0 1 2 3 4 7 8
Days Post Inoculation
Results: A. solani
5 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

30. () UTC () IS Check () 2.5 µL/L () 5 µL/L () 7.5 µL/L () 10 µL/L
S. sclerotiorum in vitro
60
50
40
Diameter in mm
Diameter (mm)
30
20
2.5 µL/L 10
0
-10
0 1 2 3 4 7 8
Days Post Inoculation
Results: S. sclerotiorum
2.5 µL/L was capable of inhibiting S. sclerotiorum growth completely in
vitro.
Untreated Control

31. Objectives
 Can this volatile compound control other
 Which volatile compound is the most effective and at
what concentration in vitro?
potato pathogens in vitro?
 2E-hexenal at 5 µL/L for potato blemish pathogens
 7.5 µL/L 2E-hexenal toxic to all tested
 Can this volatile compound control other potato
pathogens in vitro
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?

32.  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

33. 2.5 µL/L
C. coccodes germination in vitro
2.5 µL/L capable of completely inhibiting C. coccodes conidial germination
in vitro.
Untreated Control

34. 2.5 µL/L
C. coccodes hyphal elongation in vitro
2.5 µL/L 2E-hexenal capable of significantly decreasing hyphal elongation of
C. coccodes in vitro.
Untreated Control

35. 2.5 µL/L
H. Solani germination in vitro
2.5 µL/L capable of strongly inhibiting conidial germination in vitro. H.
solani has a notably slower rate of germination than C. coccodes.
Untreated Control

36. 2.5 µL/L
H. Solani hyphal elongation in vitro
2.5 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.
Untreated Control

37. C. acutatum untreated cell
Results: Mode of Action
C. acutatum : 2E-hexenal
 C. coccodes  2E-hexenal inhibits C. coccodes and
H. solani conidial germination and
 Blackdot significantly reduces hyphal
elongation
 H. solani
 Silver Scurf  Other research has shown that 2E-
hexenal scrambles cellular
membranes disrupting organelles
C. acutatum untreated cell and important cellular functions
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

38. Objectives
What is the mode of action of this volatile
 Which volatile compound is the most effective and at what

concentration in vitro?
compound? 5 µL/L for potato blemish pathogens
 2E-hexenal at
 2E-hexenal inhibited conidial
 Can this volatile compound control other potato pathogens in
germination as well as hyphal elongation
vitro?
 7.5 the 2E-hexenal toxic to all tested pathogens in vitro
in µL/L blemish pathogens C. coccodes
 What is theH. solani
and 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?

39. Large Scale Trials In vivo methods
(C. Coccodes)
Small Scale Trials
Molecular and Visual Quantification

40. Results: C. coccodes large-scale trial
The amount of C. coccodes present on naturally infected potatoes increased over time in storageover 5 months
Under large-scale experimental conditions, 2E-hexenal did not inhibit the growth of C. coccodes on the
in storage.
untreated control.

41. Results: in vivo large-scale trial
 Results indicate that 2E-  Poor circulation of 2E-
hexenal was not effective in hexenal
controlling C. coccodes in
vivo, why?  Respiring potatoes may
interact with 2E-hexenal and
Improvements decrease concentration
 Small-scale trials designed to  Broad sample collection
over come these possible times
issues
 C. coccodes does not spread
in storage, symptoms
worsen

42. In vivo methods
Small Scale Trials
Un-inoculated Tubers
Potatoes tuber peel (2 2E-hexenal
Both the treated with mm) and tuber
absorbed the volatile compound for up
tissue absorbed 2E-hexenal, absorption
to 5 independent of treatment volume
was days after treatment
and tuber surface area
Molecular and Visual Quantification

43. 50 µL/L
Results: C. coccodes small scale
Under small-scale experimental conditions, 2E-hexenal did not inhibit the
growth of C. coccodes In vivo.
Untreated Control

44. Pit Rot Symptoms
Bacterial Soft Rot Symptoms
50 µL/L
All replications
Results: P. atrosepticum small-scale trial
Under 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.
Untreated Control

45. 0
All replications
121
UTC 25 uL/L IS check
5 uL/L 50 uL/L
100
a. Phytophthora erythroseptica
90
Percentage of infected tissue
80
70
60
50
50 µL/L
40
30
20
10
0
All replications
100
Results: P.ultimum
90
b. Pythium erythroseptica
of infected tissue
Under small-scale experimental conditions, 2E-hexenal did not inhibit the
80
growth of P. erythroseptica in vivo.
70
Untreated Control
60
50

46. 10 All replications
0
UTC 25 uL/L IS check
5 uL/L 50 uL/L
100
b. Pythium ultimum
90
Percentage of infected tissue
80
70
60
50
40
50 µL/L 30
20
10
0
All replications
UTC 25 uL/L IS check
Results: P. ultimum 50 uL/L
5 uL/L
Under experimental conditions, 2E-hexenal did not inhibit the growth of P.
ultimum in vivo.
Untreated Control

47. 50 µL/L
Results: H. solani
Under experimental conditions, 2E-hexenal inhibited the growth of H.
solani in vivo at the minimum treatment volume of 5 µL/L.
Untreated Control

48. Results: in vivo small-scale trial
 Low oxygen conditions (P.
 Results indicate that 2E-
atrosepticum) due to
hexenal controlled H. solani increased treatment
in vivo but nothing else, concentrations
why?
 Anoxic conditions lower
Improvements potato defense mechanisms
 Decrease treatment volumes  Rot pathogens penetrate
 Decrease treatment time
tuber tissue deeper than
volatile
 Increase oxygen presence
 C. coccodes microsclerotia
and volatile circulation
 H. solani rapid sporulation on
 Treat prior to inoculation
tuber surface

49. Objectives
 Which volatile compound is the most effective and at what
 Can this volatile compound control these
concentration in vitro?
pathogens in 5 µL/L for potato blemish pathogens
 2E-hexenal at
vivo?
 2E-hexenal inhibited H. solani in vivo at 5
 Can this volatile compound control other potato pathogens in
µL/L
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

50. 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

51. 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

52.  Low treatment volumes
 Fumigation
Applications:
 Active packaging
With further research, 2E-
hexenal could be used to  Further research
control the growth of  Improved In vivo studies
postharvest potato pathogens,  Inclusion complexes and
and an alternative to polymeric plastic films
postharvest fungicides. (packaging)
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.

53. Committee:
Phillip Wharton
Nora Olsen
Joe Kuhl
Rafael Auras
Potato Pathology Crew:
Tim Miles
Laura Miles
Katie Fairchild
Darrah Ricard
Equipment Support:
Joe Kuhl
Pamela Hutchinson
Louise-Marie Dandurand
Thank you for your time.

54. Thank you for your time 