A Database for Triticeae and Avena
INSTITUT FÜR PFLANZENGENETIK UND KULTURPFLANZENFORSCHUNG (IPK)
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.