Schriften zu Genetischen Ressourcen - Genres

Diversity in barley (Hordeum vulgare)
nificant decrease so that the variation in wild barley (ssp. spontaneum) is higher than
in landraces and even more so than in modern varieties, as shown in several studies
(cf. GRANER et al. 2002). The larger variation in ssp. spontaneum is partly due to the
higher degree of outbreeding (up to 10-12 % of outcrossing has been reported, cf.
BROWN et al. 1979) than in cultivated material (usually < 1 %). Ssp. spontaneum
originally had a very large diversity due to adaptation to the versatile environments in
the Fertile Crescent. The wild form is obviously particularly variable in Israel, but collections
and investigations of material from other areas have been carried out to a
much lesser extent. According to several studies by the Israeli research group of
Prof. E. Nevo there is a very strong correlation between diversity and stress tolerance
(e.g., to salt and drought). Plants in a stressful environment are significantly
more variable than plants growing under more optimal conditions (cf. PAKNIYAT et al.
1997).
Also for landraces a number of studies based on isoenzymes, hordeins and various
molecular markers, indicate a large and often geographically related variation pattern.
Particularly variable and subject to clinal differentiation, such as to altitude, climate
or other environmental conditions, is material from Ethiopia. A comparison between
ssp. spontaneum and landraces showed a significant pattern (Table 1).
Tab. 1: Variation in isoenzymes in barley landraces and ssp. spontaneum (after
NEVO et al. 1986)
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No. of alleles detected Loci without polymorphism
Landraces
Europe 44 10
Iran 40 5
ssp. spontaneum
Iran 49 6
Israel 79 0
Several studies show that there generally has been a gradual and steady loss of alleles
over time, particularly in modern and high bred varieties. The so-called genetic
erosion should thus have been regularly depauperating the available genetic resources
making the future breeding material more vulnerable. However, there are
also other tendencies. In a study based on isoenzymes it was shown that new varieties
(released after 1990) had a reduced variation amplitude compared to earlier varieties
of Nordic and Baltic origin, which in turn had a more narrow variation than exotic
landraces from C Asia (KOLODINSKA et al. 2001). This trend is also obvious in a
broad survey of molecular markers by GRANER et al. (2002). These authors show
that in most cases a new cultivar has a reduced diversity in comparison with the
foundation lines.