Page 57 - Volume 1, Issue 2, July 2008

Wild oat variability in Greece 109
dicate presence of wild oats in 91% (2007)
and 83% (2008) of the wheat fields in Vi-
otia. Not shown in the table but impor-
tant to note is that the density of wild oats
in these fields, although usually moderate
to light, was at times very high. The high
frequency of occurrence (83-91%), even
in moderate or light densities at a time
near harvest, shows that wild oats are an
important weed for wheat crops in Viotia
taking into account that the results of this
survey reflect plants having escaped the
use of herbicides which is a widely adopt-
ed practice in the region.
The results of the survey also show
that A. sterilis is the species occurring in
all wheat fields in which presence of wild
oats was recorded (83-91%of the surveyed
fields) while A. fatua was found only in 11-
15% of the surveyed fields, always coexist-
ing with A. sterilis (Table 1). In fact, A. fatua,
whenever found, was in small patches and
low plant densities within a more spread
and dense population of A. sterilis.
Our results on the relative abundance
of the two wild oat species are consistent
with results from similar surveys conduct-
ed several years ago in Spain which indi-
cated frequencies of 32 and 8%, for A. ster-
ilis and A. fatua, respectively (7), while in
another survey in Andalusia, A. sterilis was
the most frequent grassy species (being
present in 65% of the surveyed fields) and
A. fatua was hardly found at all (9).
The presence of A. fatua in cereal crops
in Greece has for long been questionable.
Thus, in previous weed surveys conduct-
ed in Central Greece it was not found at all
(1) while in other publications its presence
in the country was reported to be rather
limited (2, 3) or doubtful (15). The results
of this survey prove the actual presence of
A. fatua in cereal crops of Greece at low,
but probably increasing, frequencies and
densities.
The recognition of the Avena species,
especially the distinction of A. fatua from
A. sterilis , is not easy and seems rather im-
possible at growth stages before matura-
tion. A detailed study of the mature spike-
let characters as they appear at the time
of shedding indicated that the two spe-
cies have some clear differences (Table 2)
which can be used for the in situ recogni-
tion of the species.
The spikelet characters used for the in
situ species recognition (Table 2) were se-
lected after many appropriate compar-
isons of mature spikelets from the sur-
veyed wheat fields and standard samples
of the two species kept in the Herbarium
and the weed seed collection of the Weed
Table 1. Frequency of presence of Avena species in wheat fields in the Viotia region (8 subre-
gions, A-H) during 2007 and 2008.
Year Avena species
Number of wheat fields surveyed in each subregion Frequency
(%)
A B C D E F G H Total
2007
Surveyed fields 8 6 5 3 6 6 4 7 45
Avena-free fields 1 1 0 0 0 1 0 1 4 8.9
Avena sterilis 7 5 5 3 6 5 4 6 41 91.1
Avena fatua 1 1 0 1 0 0 0 2 5 11.1
2008
Surveyed fields 5 8 7 5 5 6 4 8 48
Avena- free fields 1 0 1 1 1 2 0 2 8 16.7
Avena sterilis 4 8 6 4 4 4 4 6 40 83.3
Avena fatua 1 1 2 0 0 0 0 3 7 14.6