Download 2. Eyespot - MacKillop Farm Management Group

2. Eyespot - Variety Tolerance in Commercial Varieties
Margaret Evans ([email protected]) & Hugh Wallwork ([email protected])
SARDI, Plant Research Centre, Urrbrae
KEY MESSAGES
Findings are from one site in one season and more data will be needed before firm
recommendations can be made.
• Where eyespot inoculum is present in paddocks at medium to high levels, avoid sowing
Wedgetail and Orion. Trojan, Manning, and DS Pascal would be better choices, as would
Compass if sowing a barley.
• Experience across 6 screening trials undertaken in SA in 2014 and 2015 indicates that some
varieties (e.g. Trojan, Compass) are very consistent in their response to eyespot, but others (e.g.
Hindmarsh, La Trobe, Corack, Shield) are not.
• Cereal types and varieties with weak straw are more likely to be at risk of lodging (and harvest
difficulties) in the presence of eyespot than those which have good straw strength. Plant
growth regulants might assist in reducing lodging issues.
• The range of susceptibilities shown within the varieties screened should provide a good base
for breeding programs.
Why do the trial?
These variety and fungicide efficacy trials have
assisted in identifying resistance sources for
eyespot and have provided data to support
chemical companies acquiring label extensions
to register fungicides for use against eyespot in
cereals in Australia.
Eyespot is an increasing problem in the higher
rainfall grain growing areas of SA such as
lower Eyre Peninsula, the Cleve Hills, the mid
North, the Adelaide Plains and the South East.
This increase is mainly due to farming systems
moving to systems with increased stubble
retention, direct drilling and an increasing
number of cereals in rotations. In Australia,
eyespot in cereals is caused by the fungus
Oculimacula yallundae (previously known as
Pseudocercosporella herpotrichoides) which
infects stem bases causing the eye-like lesions
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Wheat Agronomy Trials
which gives eyespot its name. Figure 1 below
shows eyespot lesions on the stem. Rain splash
of spores from infected residues infect the bases
of stems and produce lesions with a typical
eye shape. The outside of the “eyes” vary in
colour from quite dark-brown through goldenbrowns to a light almost greyish colour – this is
equivalent to the “eyesocket”. Then there is a
lighter often bleached looking “iris: with black
spots and blobs in the middle for a “pupil”. The
black is from fungal hyphae (not spores). The
stem tissue in the area of the “iris” and “pupil” is
weakened and sometimes can feel quite soft if
pressed on (why lodging occurs).
Yield losses from this disease occur as a direct
result of the stem lesions and, secondarily,
from plants lodging due to weakened stem
bases which can make it difficult or impossible
to harvest affected plants. Overseas, eyespot
control includes fungicide application and the
use of partial resistance in varieties. As eyespot
has had a restricted distribution in Australia, no
fungicides have been registered for control of
eyespot in cereals and little has been known
about resistance levels in Australian varieties.
Figure 1: Eyespot lesions on the stem of a plant
GRDC has funded a 2 year program to assess
varietal resistance in Southern Australian
germplasm. Information presented here is from
one variety screening trial undertaken in the
South East of South Australia in the second year
of the research program. Results from screening
trials undertaken elsewhere in South Australia (3
sites in each of 2014 and 2015) are available on
request.
How was it done?
The Kangaroo Inn site was located on Richard
Kirkland’s property in a paddock which has had
a history of eyespot problems. High levels of
eyespot inoculum (2 million copies – extremely
high compared with other paddocks having
eyespot problems) were present in the site at
the start of 2015.
To encourage eyespot expression, the trial was
sown as early as practicable (19th May) with
high plant density (250 plants per m²) and with
good N levels (140kg DAP + Impact at sowing
and 65 kg/ha urea on 8th July). Seed was
treated with insecticide to reduce barley yellow
dwarf virus issues. The site was on a black loam,
plots were 8 rows (1.2 m) wide by 10 m long and
3 replicates were used in a randomised block
design.
Seven bread wheat, fourteen long season
wheats and two barley entries were screened
for resistance to eyespot. Entries were chosen
after consultation to include locally grown
varieties, to represent a range of genetic
backgrounds (including genes for resistance
to crown rot) and to have some commonality
with screening trials at Cummins, Tarlee and
Templers.
Stem samples were assessed for eyespot
expression on 5th December, when plants
were at late grain fill. A total of 25 stems were
assessed in each plot, with 8-9 stems taken from
each of 4 inner rows of the plot (excluding the
central row and outer rows).
A scoring scale of 0-3 was used, where:
0 = no lesions.
1 = slight eyespot – small lesion(s) on less than
half the stem circumference.
2 = moderate eyespot - lesion(s) on at least half
the stem circumference.
3 = severe eyespot – lesion(s) girdling the whole
stem; tissue softened, lodging would occur
readily.
Wheat Agronomy Trials
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This scoring scale allowed calculation of
eyespot incidence (% stems with lesions – an
indication of potential for yield loss) and severity
(an eyespot index which indicates the actual
severity of disease pressure). The eyespot index
ranges from 0 (no stems with lesions) to 100 (all
stems girdled by lesions).
Plots were scored for lodging on 5th December,
with the % of the plot showing lodging being
recorded. Figure 2 shows an example of
lodging in a crop infected with eyespot.
Figure 2: Lodging in a Mace wheat crop on the
Eyre Peninsula
What happened?
The trial established well and weeds, other
diseases and insect pests were adequately
controlled.
The incidence and severity of eyespot were
intermediate at the site, due to few rainy days
during tillering and early stem extension. This
was indicated by only 55% of Mace stems
having eyespot lesions (compared with 94%
at Tarlee in 2014) and the eyespot index (an
indication of severity of eyespot expression) for
Mace being 30 (compared with 90 at Tarlee).
Trends exhibited by eyespot incidence and
severity data were very similar for all entries, so
only results for eyespot incidence are presented
here.
Wheat varieties with the highest incidence of
eyespot at Kangaroo Inn included Wedgetail,
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Wheat Agronomy Trials
Orion, Mace, Gazelle Forrest, Kiora and Wakelin
(Fig. 3). Wheat varieties with the lowest eyespot
incidences (Fig. 3) included Trojan and two
long season wheat varieties which each have a
gene that confers partial resistance to eyespot
- Manning (Pch1 gene) and Einstein (Pch2
gene). Varieties with low incidences of eyespot
included Brennan, Corack, DS Pascal and
Viking.
Lodging information is not presented here as
it was not always clear whether eyespot was
the cause of the lodging. Orion lodged badly
(average 87% of each plot), while Kiora, Condo
and Brennan exhibited 30% or more lodging.
Compass and La Trobe both had low
incidences of eyespot (Fig. 3), but lodged badly
due to seasonal conditions, with over 60% of
each plot being affected.
What does this mean?
Results from the Kangaroo Inn trial should be
considered in the context of results from trials
undertaken at other sites in SA (see Fig. 2 for
results from Tarlee) until more information is
available from the South East.
Experience across all screening trials (and as
demonstrated in Figure 4) indicates that:
1. Some varieties are very consistent in
their response to eyespot. These include
Compass and Trojan which both exhibit low
incidences of eyespot.
2. Many varieties are not consistent in
their response to eyespot. These include
Hindmarsh, La Trobe, Corack and Shield,
which often, but not always, exhibit high
incidences of eyespot.
Where eyespot inoculum is present in paddocks
at medium to high levels, avoid sowing
Wedgetail and Orion. Better choices would
be Trojan, Manning and DS Pascal as would
Compass if sowing a barley.
There is some indication from other screening
trials that cereal types or varieties with weak
straw strength will be more susceptible to
lodging if stems are damaged by eyespot
lesions. This is not unexpected, but should be
considered if choosing a crop type or variety
for a paddock where eyespot is present.
Plant growth regulants have potential to
reduce lodging where eyespot is present by
strengthening and shortening stems, but the
economic benefits of this would need to be
considered.
Einstein is an ultra-long season wheat which is
unlikely to be grown in our environments and
farming systems, but together with Manning
should provide good material for breeding.
Data from this variety screening trial will be
provided to breeders to feed into their breeding
programs.
Eyespot incidence
Kangaroo Inn, sown 19 May 2015
100
Barley
Stems with eyespot lesions (%)
90
Long season wheat
Wheat
80
70
60
50
40
30
20
10
Wedgetail
Orion
Mace
Gazelle
ADV09.0480
ADV08.0062
Forrest
Kiora
Wakelin
Lancer
Revenue
Condo
Shield
Wallup
Viking
DS Pascal
Corack
Brennan
Manning
Compass
Trojan
La Trobe
Einstein
0
Figure
3. Effects
cerealtype
type and
onon
eyespot
incidence
– Kangaroo
Inn, 2015.Inn, 2015.
Figure
3. Effects
of of
cereal
andvariety
variety
eyespot
incidence
- Kangaroo
Eyespot severity
Tarlee, sown 21 May 2014
100
90
Barley
Wheat
Durum
Wheat Agronomy Trials
45
Figure 3. Effects of cereal type and variety on eyespot incidence – Kangaroo Inn, 2015.
Eyespot severity
Tarlee, sown 21 May 2014
100
90
Barley
Wheat
Durum
Disease index
80
70
60
50
40
30
20
FigureFigure
4. Effects
of cereal
varietyonon
eyespot
severity
- Tarlee
(mid North),
4. Effects
of cerealtype
typeand
and variety
eyespot
severity
– Tarlee
(mid North),
2015. 2015.
ACKNOWLEDGMENTS
This project was funded by GRDC through
DAS0139 “Improving grower surveillance,
management, epidemiology knowledge
and tools to manage crop disease in South
Australia”. Thanks to Richard Kirkland and
family for providing a trial site on their
property at Kangaroo Inn and to Neil Nolan
(Naracoorte Agricultural Services) for assisting
in finding the trial site and selecting the entries
used in the trial. Thanks also to Amanda
Pearce, Matthew Hoskings and the SARDI
New Variety Agronomy team at Struan for
managing the site, changing spore trap tapes
and helping with collecting samples.
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Wheat Agronomy Trials