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Good morning and welcome to my talk on ’The effect of small shifts in climatic conditions on leaf
blotch diseases in Norway. ‘During my talk I will present data of leaf blotch diseases in different
years and field locations and what climate factors are correlating with disease development. So I am
not talking about how a changing climate will effect disease in the future, but focus on how climate
might have effected disease in the past.
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When I talk about leaf blotch disease, I actually talk about a complex of 3 pathogens causing similar
disease symptoms : Septoria tritici, teleomorph Mycospaerella graminicola causing leaf blotch,
Stagonospora nodorum, teleomorph Phaesopharia nodorum,causing glumeblotch and Drechslera
tritici-repentis, teleomorph Pyrenophora tritici-repentis causing tan spot. You can see the symptoms
on wheat leaves here: light to dark brown yellow spots of various sizes. They are very difficult to
distinguish between each other and easily confused with leaf senescence as they appear at the end
of the season, when leaves become yellow anyway.
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So how do these pathogens survive the winter, grow, spread and cause damage? All three pathogens
are saprophytic, being able to utilize dead plant material. The initial inoculum can come from the
seed itself, as Stagonospora and Drechslera are seedborne, last year’s wheat straw lying on the top
of the soil in form of picnidia produced by Stagonospora and Septoria or sporulating colonies
produced by Drechslera, or volunteer plants covered with pseudothecia by all three pathogens.
However, as long as it is dry, conidia won’t be released and splashed onto the seedling leaves,
colonies won’t sporulate much and the ascospores from the pseudothecia won’t germinate. The
epidemic only gets started when we get
RAIN under moist conditions, conidia will be splashed onto the seedling leaves, ascospores will
travel long distances through the air and germinate, together with the conidia released from the
Drechslera colonies that now start to sporulate extensively. As rain events continue to occur, we will
get secondary cycles, more and more spores, disease spread through the field and adjacent fields
and soon the leaves will be covered in leaf blotches significantly reducing grain yield. The higher the
temperature the shorter the latent period, the faster the spread.
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When we started this work on leaf blotch diseases, the objective was to analyze historical data on
disease assessments and see if disease severity has been increasing in the last decades as we knew
the climate has been changing and the growing season is starting earlier every year. We utilized field
data from pesticide and varietal trials from the Nordic field trials, the ViPS data and seed infection
data from the Kiemen Seed laboratory. The data was collected from South Eastern Norway, the main
wheat growing area, in particular from Vestfold, Østfold, Hedmark, Romerike and Oppland and we
used data from spring wheat varieties Avle, Zebra, Bastian, Bjarne and winter wheat varieties
Mjølner, Bjørke, Magnifik and Olivin.
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Leaf blotch disease in time and space…
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To the data: This graph shows percentage of seed lot infection with S. nodorum from 1974 till 2008.
You can see that there have been periods of high disease severity, as here in the late 70s beginning
of 80 and in the beginning of this century from 2000 till 2004. 2006 seemed to be the lowest severity
year over the last 10 years. We do not see a continuous increase of seed infection over the last
decades. Well, that was data on Stagonospora only and the data does not tell us from where the
samples were taken. So let’s look at the field assessments.
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This graph shows leaf blotch severity in different years assessed in the field between BBCH stage 70
and 75 over the last 9 years. The small numbers in yellow show the numbers of fields assessed Again,
there is no trend towards higher leaf blotch incidence in recent years, but maybe the time frame is
too short. What we do see it that despite the fact that we have a limited number of trials per year
and despite the fact that we integrated different locations, and different varieties, we do see
significant differences between years, namely between high severity years 2003 and 2007 and the
low severity year 2006. So in the last 10 years, both data sets point to a low severity year 2006.
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What about differences in location? This graph shows leaf blotch severity on winter and spring wheat
in Hedmark, Oppland, Romerike, Østfold and Vestfold over the last 9 years. There is too much
variation between years in Oppland and Hedmark, but LBD severity in Østfold is significantly lower
than in Vestfold and Romerike. Why would that be? There could be many reasons, but as I said
earlier, rain and temperature are determinators for the epidemics, so lets look at accumulated
precipitation in Vestfold and Østfold.
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This graph shows accumulated precipitation in mm from the beginning of the growing season until
the end and degree days. There is significantly higher precipitation in Vestfold than in Østfold over
the time period from 2002 till 2009. That does make sense and it is somewhat intuitive. However,
let’s take a closer look at LBD severity over time at these two locations.
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This graph shows leaf blotch disease severity in different years on spring wheat at Vestfold and
Østfold. Overall, Disease severity is always higher in Vestfold than in Østfold, but really significant
differences can only be found in 2003, 2008 and 2009. In 2004 and 2005 we did not have the data to
do any comparison and in 2002 and 2006, variation was to high within the locations. How do the
climate conditions in those years compare between Vestfold and Østfold?
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We first compared average monthly temperatures and degree days during the season between
Østfold and Vestfold, then we looked at accumulated precipitation between start of the growing
season and assessment time, and the number of heavy rain fall events (that is rain events above
10mm). The average monthly temperature did not differ between Vestfold and Østfold and the
accumulated rain and the number of heavy rain events did not differ between Vestfold and Østfold
during 2003, 2008 and 2009.What does that mean? Doesn’t rain and temperature play a role? I am
sure they do, but the relationship might not be as straight forward as we would wish it to be.
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What about the LBD differences between years? How do the climate conditions relate to leaf blotch
diseases in 2003 and 2006? Again we looked at average monthly temperatures during the growing
season, degree days and rain fall, accumulated precipitation and heavy rain events.
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This graph shows the monthly average daily temperature in 2003 and 2006 for Mai, June and July in
Centrigrades. Differences are small, but for May and July, we find them significant. Our assessment
date is usually mid July, so the differences in this month, might not have so much of an effect on the
symptoms development, but the temperature in May might.
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We compared the rainfall between these two years, in particular accumulated precipitation between
the begin of the growing season, 1st of May and the assessment date, 2months before the
assessment date and 4 weeks before the assessment date. We did not see differences in
accumulated precipitation between the start of the growing season and assessment between 2003
and 2006, no differences in accumulated precipitation in the last 2 months before assessment and
not in the last 4 wks before assessment. This is very counter intuitive, so let’s have a look at the data:
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This graph shows the accumulated precipitation in 2003 and 2006 during the whole season until
assessment, 2 months before and 4 weeks before. 2003 appears to be definitely showing higher
precipitation than 2006, especially during the 2 months before assessment period, but there is too
much variation between the location to see significant differences between years.
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What is causing this variation? Actually it is not the amount of rain, but the absence thereof, the dry
periods in Romerike. What do I mean with it?
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Here you see daily rainfall and temperature during the season until the assessment time in 2003 and
2006 in Romerike. Yes there is less, but consistent rainfall in Romerike 2003 than in 2006, yet we
have leaf blotch severity of over 20% in Romerike in 2003 and a leaf blotch severity of 3 % in 2006.
Why? Because the high rain events in 2006 were interspersed with long and frequent dry periods.
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So instead of looking at the accumulated rain over a certain period, we were looking at the number
and the length of dry periods in 2003 and 2006 for all locations . And as you can see in this graph,
there are significant fewer dry periods in 2003, when leaf blotch disease was high, than in 2006,
when Leaf blotch disease severity over all locations was low.
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Sooo? The data presented is taken from different experimental set ups and therefore much less
robust than data from carefully designed experiments with the goal of tracking LBD severity increase
over time, there is a lot of variation masking differences that might be otherwise significant.
However, the significant differences we do see between years and locations, despite the variation
are valid. The correlation we see between dry periods and low disease severity in the past can help
us to improve our models for future disease scenario, which are often based on average rainfall and
air temperature predictions.
In summary, we do not see a consisting increase in LBD severity in the past 9 years and not of Glume
blotch in the past 36 years. We see significant variation of LBD with location and between years.
Accumulated rain and average daily temperature is related to LBD severity, And the number and
length of dry periods.
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I’d like to acknowledge the help of Unni Abrahamsen from Bioforsk in Apelsvoll and my Colleague
Oleif for giving me access to the data. And Thank YOU for your attention.