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Results of the discriminant analysis suggest that ssp.
strangulata forms a very distinct division within the species.
The strangulata accessions were taller with heavier seeds,
prominent stem curvature and a rounded seed shape. The analyses also
suggest that within ssp. eusquarrosa, var. anathera is
fairly distinct from var. typica and var. meyeri. The
var. anathera accessions were clearly distinguished on awn
type and also tended to be shorter than the other accessions. The
varieties typica and meyeri were difficult to separate
and also proved to be difficult to distinguish by multivariate
analysis. Kihara et al. (1965) found intermediate and hybrid forms
between var. typica and var. anathera and between ssp.
eusquarrosa and ssp. strangulata and this may explain
some of the problems of identifying the var. typica and var.
meyeri accessions. The occurrence of intermediate forms could
explain the difficulty in distinguishing the var. typica and
var. meyeri accessions.
Ideally, effective divisions should be distinct both morphologically
and genetically. The decision by van Slageren (1994) not to formally
recognize any intraspecific classification within Ae. tauschii
was heavily influenced by the results of Kim et al. (1992). In their
study, based on a highly conserved region of ribosomal- DNA, they
were unable to find consistent polymorphism that distinguished
ssp. strangulata accessions. RFLP studies by Tsunewaki et al.
(1991) and Lubbers et al. (1991) found close similarities between
ssp. eusquarrosa var. meyeri and ssp.
strangulata; and a recent molecular study by Dvorak et al. (1998)
found evidence of gene migration between the different divisions in
accessions from the southwest Caspian area of Iran. It is evident
from these studies that morphological variation within Ae.
tauschii can not always be used to predict genetic variation at
the molecular level because phenotypic divisions become blurred due
to hybridisation and hence the occurrence of intermediate forms
(Kihara et al. 1965). There is, however, evidence of genetic
distinction at the molecular level between the different subspecies
in Transcaucasia (Dvorak et al. 1998), yet the same study also failed
to find any between var. typica and var. meyeri. This
would appear to be consistent with the lack of a clear morphological
distinction between them in this study.
The intraspecific classification for Ae. tauschii based on
plant morphology appears to be of value. In particular, the.
distinction between the subspecies strangulata and
eusquarrosa is an easy one to make; the ssp.
strangulata accessions were easy to identify and were well
separated by multivariate analysis. There is also some molecular
evidence to support the separation (Dvorak et al. 1998). This
conclusion is different to the one by Kim et al. (1992) but it is
worth pointing out that both studies have involved a limited number
of ssp. strangulata accessions. The different varieties within
ssp. eusquarrosa were less easy to distinguish, especially
varieties meyeri and typica. The lack of a difference
between these two suggests that this division is unsound to a certain
degree and this is supported by some molecular evidence (Dvorak et
al. 1998). The variety anathera may, however, be distinct
enough to retain.
Promoting greater utilization of material is now a major task for
genebanks. Other collections of Ae. tauschii have been
extensively evaluated over the past ten years and the species is
being increasingly used for wheat improvement (Murphy et al. 1997;
Mujeeb-Kazi et al. 1996; Cox et al. 1995; Yildirim et al. 1995;
Appels and Lagudah 1990). Assessing the breeding potential of the
material was obviously beyond the scope of this study but characters
of interest such as height, spikelet number and seed weight have been
scored. In addition a preliminary evaluation of resistance to stripe
rust revealed that seven of the accessions, including all five of the
ssp. strangulata accessions, showed resistance to the.
prevailing natural population of stripe rust infection. This result
is consistent with other studies in which ssp. strangulata
accessions showed greater disease resistance (Yildirim et al.
1995; Cox et al. 1995; Appels and Lagudah 1990). One accession was
found to have a tough rachis and there was significant variation
within the collection for yield related characters such as spikelet
number, seed weight, leaf length and plant height. Further evaluation
is essential W to reveal the range and potential of other
agronomically important characters.
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