Plant breeding for organic and sustainable, low-input agriculture

Identification of the components of several cultivar mixtures in Spanish wheat by means of
SSR markers
Fernando Martínez, Mar Cátedra, Pilar Rallo
Dpto. Ciencias Agroforestales, EUITA, University of Seville, Spain
Cultivar mixture is one of the proposed solutions to increase genetic diversity within a crop,
which is one of the major issues in the organic farming. Several positive effects have been
reported on cultivar mixtures, being the reduction of foliar diseases the main cited effect in the
literature. It reduces also the risk of resistance gene break-down again these diseases. Abiotic
stresses are also better buffered than in pure stands, yield stability increases and even quality of
the product can be enhanced (Finck et al., 2001).
This work aims at differentiating the pure stands within a mixture in order to overcome legal
problems in dealing with genetic diversity in the seed market.
In this work, four cultivar mixtures of bread wheat and four of durum wheat have been designed
for improving disease resistance, production and quality. All the cultivar mixtures were fourway,
i.e. composed by four cultivars. Mixtures were picked from the field (before flowering),
where 25 sample leaves were collected in order to be sure (99% probability) of getting at least
one leaf of each cultivar. Besides, mixtures were also collected from the greenhouse, where one
leaf of each cultivar was collected to create the mixture with certainty.
Five SSR markers or microsatellites were used (BARC109, BARC176, Xgwm448, DuPw67 and
DuPw254). The microsatellite DuPw167 and BARC176 were the most suitable for the
discrimination of cultivar mixtures in bread and durum wheat (Röder et al., 2002). They showed
a fair level of polymorphism. It is remarkable that, sometimes, differences in the amplification
within a mixture have been detected. That means that some alleles are better amplified than
others. This may suggest a competence of the alleles within the mixture to be amplified, which is
not desirable at all but it has been reported (Rallo et al., 2001).
In general, the level of polymorphism detected in durum wheat was higher than in bread wheat.
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