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Materials and Methods
Failures in yield in some years are often correlated with severe
fusarium head blight (Maric et al 1986). How high these
damages really are and what their maximum is in our wheat growing
areas is hard to determine for sure without exact field testing.
Therefore, adequate field trials were conducted at location Botinec,
with five wheat lines all developed by this Institute. The aim was to
determine the effect of fusarium head blight on reduction in yield.
Severe attack (epiphytotic) of the fungus was ensured by artificial
infection with a population of selected Fusarium graminearum
isolates.
Experiments were set following split-plot design in randomized blocks
with five replications. Plot size was 1 m2.
Artificial infection
was made with a suspension of spores from selected Fusarium
graminearum isolates at the flowering stage (stage 10.5 after the
Feekes-Large), late in the afternoon, thus avoiding high daily
temperature, while requirements in high relative air humidity needed
or germination, of spore were met, which ensured a successful
infection. Apart from the fact that evening dew provides optimal
conditions for the infection, artificial infection late in the
afternoon allowed us to avoid plastic foil often recommended and used
by many authors in their research. For the area where our research
was conducted, northwestern Croatia, use of plastic foil is limited
because of the high daily temperatures occurring during anthesis.
This was proved in our trials when plants, covered with plastic foil
immediately after the inoculation died because of extremely high
temperatures occurring under the foil.
Identification of Fusarium species, collected from infected
samples of spike, isolation of pure culture of Fusarium
graminearum fungus used for artificial infection, and selection
of the most suitable isolates for preparation of inoculum was made by
Viktorija Vlahovic, M. Sc. in a laboratory of this Institute,
following the well-known methods (Milatovic, Vlahovic and Tomasovic,
1982; Bekele 1984; Liu 1984; Luzzardi 1984).
Severity of fusarium head blight attack was rated by an
international scale (Tomasovic 1987) at the milk- dough stage (stage
11.1 and 11.2, Feekes-Large). Other details referring to the
mentioned rating scale are discussed in paper by Tomasovic (1987)
and Milatovic, Vlahovic and Tomasovic (1982). Other
management practices usual for trials of such type and purpose were
applied. In both years of research trials were treated for weed
control.
Results and Discussion
After adequate statistical data processing, analysis of variance
showed that both tested factors, artificial infection and variety, as
well as their interaction did not always have statistically
significant effect on yield in both years (Table
1). From those
two factors, only artificial infection had a statistically
significant effect on yield in both years. The significance of this
effect was demonstrated in "F" and "t" tests. Thus, reduction in
yield in 1985 ranged from 53 to 70% and in 1986
from 51 to 53%. Such severe reductions in yield
because of the disease should not only be attributed to artificial
infection, but also to actual climatic conditions that favoured the
occurrence and development of the disease. This especially refers to
the second year of investigation (1986) when moderately severe attack
of natural fusarium head blight was observed, which, of course,
reflected on percentage of total yield loss in that year. In this
way, yield reduction was seemingly lower, though one would not tell
that judging by the climatic conditions. Therefore, in presenting
data, estimates of fusarium head blight attack both from natural
conditions and artificial infection have to be given. Naturally,
disease attack must be rated by an accepted international scale and
within optimal therm, so that the obtained results can be compared
with the results already obtained both in this country and from
worldwide.
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