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Open Discussion Notes, Wednesday, July 13th, 2011 (pdf....)
Questions on Spongospora and Powdery Scab
How
long do sporosori survive?
Literature suggests at least 14 years
Some crops reduce infestation of soils(Brassicas, Datura)
Resting spore germination stimulated by wheat,
Datura
Bait crops (e.g. tomato, Solanum sisymbriifolium has been used to stimulate hatch of potato
cyst nematode eggs, so could possibly stimulate germination of Sss resting spores)
Recent research where germination has been
assessed in bioassays indicates between 2 and 50% of resting spores in
sporosori are released
Relative
importance of seed tuber and soil inoculum
Seed tube inoculum transmits pathogen to
disease-free fields
Soil inoculum potentially causes much more
severe powdery scab
Zoospore
behavior
Diriwaechter suggested zoospores survive for at
least 2 hours
Zoospores could swim for at least 0.5 m (Ueli
Merz)
Irrigation water could transmit sporosori and
zoospores
Scottish irrigation recommendations during
tuber set period, small amounts of irrigation (12-18 mm rather than normal 25
mm)
Tuber initiation over a 2-4 week period
Drip irrigation could be used to apply
pesticide (e.g. fluazinam) at critical period
When
does infection occur?
Root infection occurs very early in plant
growth, (within a few hours after inoculation in bioassays and within 1 week in
pot experiments)
What
are the mechanisms of plant resistance?
Likely to operate at the stage of zoospore infection
of root or stolon epidermis cells, or entry of zoospores to lenticels.
Zoosporangium development may be inhibited
Release of secondary zoospores may be reduced
Zoosporangium development and sporosorus
development (in root and stolon galls and in tuber lesions) are different life
cycle stages, and may be affected by different host resistance mechanisms
Zoospore infection is through host root and
stolon membranes
There is some relationship between root
infection and tuber infection, but this is not consistent. Cv. Swift is an
extreme example, which is almost immune to tuber infection but gets severe root
galling. Cv. Russet Burbank is moderately resistant to tuber infection but gets
severe root galling
Why are cultivars with russet tubers less susceptible
to tuber infection? Is this simply because lesions are less visually obvious?
The Spongospora life cycle
Still to be fully outlined, particularly
relating to sexual reproduction
Cultivars
and resistance
Comparisons between russet skinned cultivars
and non-russet cultivars
Is tuber skin thickness a factor in resistance?
Suberisation period; is this related to tuber
resistance?
Can penetrometer measurements be used to
predict tuber resistance?
Can root, stolon or tuber DNA content be used to
predict tuber resistance (to root or tuber disease)?
Potential
future research projects
1.Expand
collaborative project to monitor effects of climate (temperature and rainfall)
on root galling and tuber powdery scab
[European trials completed]
Co-ordinated
trials
Countries
include: Switzerland, South Africa, Israel and Sri Lanka
Common
cultivars (Netherlands supplied cultivars), e.g. Nicola, Valor, Agria
Protocol
used for European/Australian trials to be provided by Ueli Merz.
2. More Sss collections from different regions to
be sent to Rebecca Gau for genetic characterisation
3.
Irrigation
sequencing for reducing powdery scab on susceptible cultivars
4. Timing of
infection and exploring mechanisms of resistance (possible PhD project with Jacquie
van der Waals
5. Green
fluorescent protein marker into Sss
6. Integrated
disease management for powdery scab [this approach has already been widely
suggested, incorporating several disease control strategies into best practice
for growers]
7. Methods
for controlling/preventing root galling
8. Effects of
micronutrients on host resistance, on Sss, and on the structure rhizosphere
microbial community (use of metabolic profiling techniques)
9. Can soil
samples routinely taken for nematodes be used for detection of Sss, using PCR techniques? SASA
(Scotland) currently charge BP 138 per sample. Could the Scottish service be used
internationally?
10. Survival
of Sss in sludge, compost or irrigation water, and these as sources of crop
infection
11. Soil
factors affecting Sss and powdery scab.
Do suppressive soils exist, and if so, what are their characteristics?
Information from the Australian MASH trials
12. Trap
crops/Rotation crops. Do they provide a possible powdery scab management
strategy? What are the mechanisms (direct toxicity to Sss or stimulators of resting spore germination)
Outputs from the 13th European
Powdery Scab Workshop
All participants
committed to providing an Abstract (approx. 400 words) of their presentations,
to Ueli Merz by 31 July 2011
PowerPoint
presentations can be presented on the Spongospora website (individuals can
choose this option)
Next Workshop: Possibly, this will
be held in South Africa in 2014 or 2015
For the protocol: Richard Falloon
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