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Ae. tauschii is the D genome donor of bread wheat (McFadden
and Sears 1946) and is known to provide bread wheat with many
qualities including bread making quality (Orth and Bushuk 1973), cold
hardiness (Limin and Fowler 1981) and salt tolerance (Schachtman et
al. 1992). Genetic variability within the D genome of wheat is much
lower than it is within Ae. tauschii (Appels and Lagudah 1990;
Lagudah et al. 1-991) so the species offers great potential for wheat
improvement. Utilization of the species for wheat improvement is
further aided by the ability of the chromosomes of Ae.
tauschii and the D genome chromosomes of wheat to recombine
naturally.
The species has been well collected in the past and many collections
are now being evaluated for useful agronomic characters such as pest
and disease resistance (Murphy et al. 1997; Mujeeb-Kazi et al. 1996;
Cox et al. 1995; Yildirim et aL 1995; Appels and Lagudah 1990).
The aim of this study was to characterize 54 accessions of Ae.
tauschii held at the John Innes Centre, Norwich, UK and to
determine whether Eig's divisions of the species were valid.
Materials and methods
The plant material studied represents 54 accessions of
Aegilops tauschii held at the John Innes Centre, Norwich, UK.
Four pots of each accession were sown in mid-December with five seeds
in each pot. The plants were grown in an unheated glass-house until
mid-April when they were planted out in experimental plots at the
John Innes Centre. The four pots of each accession were planted
intact to give a close group of up to 20 plants, with a one metre
space between accessions.
An initial, visual assessment of variability within the collection
identified 21 characters that were easy to score, appeared to vary
between the accessions and made an obvious contribution to the plant
phenotype. These were habit, height, stem curvature, peduncle length,
leaf length, leaf width, glume colour, glume hairs, glume beak, upper
glume apex, awn length, awn colour, awn type, brittle rachis, spike
length, spikelet number, spike density, number of seeds per spikelet,
seed weight, seed shape and seed colour. Susceptibility to stripe
rust, Puccinia striiformis, was also scored.. Two further
characters, rachis segment length and spike yield, were derived from
these characters. Well-defined descriptors were produced for each
character. Many of these were based on standard descriptor
recommended by IPGRI (IBPGR 1981) but for stem curvature, peduncle
length, leaf width, glume beak, upper glume apex, awn length, awn
type, seed shape, distance between spikelets and spike yield, new
descriptor states had to be defined. A full descriptor list is given
by Knaggs (1999). Each character was scored over a few days to allow
a direct comparison of the character between accessions. Eight
replicate measurements were taken for each measured character and a
mean score calculated.
The descriptions of each subspecies and variety given by Eig (1929)
were used to identify each accession. Linear discriminant analysis
was then used to test the classifications given by the intraspecific
identifications. The test works by calculating the smallest squared
distance (Mahalanobis distance) to the group mean and then classifies
the accession within that group. There is no need to make any
assumptions about the underlying distribution of the data but the
test does assume equal covariance matrices for each group. Sixteen
characters were used for the analysis. Eight characters were
discounted for various reasons: rust susceptibility is not a
morphological character; leaf width, awn length, distance between
spikelets and spike yield were too highly correlated with other
characters; glume hairs and seed colour did not actually vary between
the accessions and brittle rachis did not vary enough. 'The analysis
was carried out using the Minitab computer program.
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