Changes in the genetic structure of wheat germplasm accessions during seed rejuvenation

Changes in the genetic structure of wheat accessions caused by interspecific competition during periodic seed rejuvenation at a gene-bank were studied. Electrophoretic patterns (Acid-PAGE) of gliadin storage proteins were used to discriminate bread from durum wheat and to identify bread-wheat genotypes. Bread wheat shows high selective advantage over durum wheat and its frequency increased up to 100% after seven rejuvenation cycles. The number of bread-wheat genotypes identified in each entry varied from five to 13, but only a few prevailed and these were different in each accession. In most cases, bread wheat was already present in the field sample collected, but at low frequency. In one case, ‘seed flow’ was thought to have occurred at a very low rate among neighbouring plots. The implication of these findings for genetic resources conservation are: 1. Mixtures of wheat species within the same germplasm accession must be avoided; 2. Only in some cases are low planting densities effective in reducing competition; and 3. The genetic structure of accessions in the gene banks must be monitored.