A Database for Triticeae and Avena
INSTITUT FÜR PFLANZENGENETIK UND KULTURPFLANZENFORSCHUNG
Corrensstraße 3, 06466 Gatersleben, Germany.
In gene banks worldwide, about six million accessions of cultivated
crops are conserved, including about 750,000 wheats. One of the
main challenges for gene banks is maintenance of the genetic integrity
of accessions. The contamination by foreign pollen or incorrect
handling during multiplication may affect the genetic identity
of the material. Molecular methods assessing genetic variation
at the DNA level will be useful to prove the purity of genebank
accessions after long-term maintenance.
Eight wheat accessions differing in their frequency of multiplication
were selected randomly out of the Gatersleben genebank wheat collection
consisting of about 17,000 accessions in total. For each accession,
samples of grain and complete spikes are deposited as vouchers
when they are grown initially. Although the samples are stored
at room temperature and, therefore, have lost their germinability,
it is still possible to extract DNA for comparative studies. Living
seed material originating from the most recent regeneration are
stored at a temperature of 0°C.
Grain derived from the first and last regeneration cycles was
used to study the genetic identity of wheat accessions regenerated
up to 24 times using wheat microsatellite markers. No contamination
resulting from cross pollination or erroneous handling during
harvesting, threshing, or labeling was detected. For one accession
(TRI 4599), genetic drift was observed, whereas for TRI 249, a
heterogenous situation for two markers was maintained over the
years. We concluded that microsatellites can be used as a simple
and reliable marker system for the verification of the integrity
and genetic stability of genebank accessions.
Wheat breeding programs worldwide successfully have exploited
the GA-insensitive dwarfing genes Rht1 (Rht-B1b)
and Rht2 (Rht-D1b). The corresponding loci Rht-B1
and Rht-D1, which are located on chromosomes 4BS and 4DS,
respectively, were mapped recently using RFLP markers (Börner
et al. 1997, Theor Appl Genet 95:1133-1137). As a result
of somaclonal variation, a mutant showing no response to GA was
detected in barley (Falk 1994, Barley Genet Newslet 24:87-89).
This mutant, which carries a dominant GA-insensitive dwarfing
gene (Dwf2), was of extremely short stature and resembled
wheat plants that have the very potent dwarfing genes/alleles
Rht3 (Rht-B1c) or Rht10 (Rht-D1c),
which are on chromosomes 4BS and 4DS, respectively. Using RFLP
and microsatellite markers, Dwf2 was mapped on the short
arm of barley chromosome 4H at a position homoeologous to the
multiallelic Rht-B1 and Rht-D1 loci. The colinearity
of the molecular markers confirms the hypothesis that a homoeoallelic
relationship exists between the GA-insensitive dwarfing genes
of wheat and barley.