Variations in seed dormancy and rates of development of great brome, Bromus diandrus Roth., as adaptations to the climates of southern Australia and implications for weed control

Abstract

Seeds of great brome, B. diandrus, were collected from 14 sites across southern Australia and sown at Perth, W.A. The duration of seed dormancy varied among the seed accessions when produced at the common field site of Perth, which suggested that variations in dormancy were genetically controlled. The environment of Perth shortened the duration of dormancy in all the accessions but did not affect their ranking, indicating a lack of genotype x environment interaction. The duration of dormancy was positively correlated (r = 0.78) with the duration of the rain-free summers of the site of collection. Dormancy was not due to hard-seededness and non-dormant seeds germinated within 40 h of wetting at 20¦C. The seed dormancy was limited to about 5 months under the storage conditions examined. Dormant seed was stimulated to germinate by gibberellic acid (2.89 mM) and dormant seed of the accession from Geraldton also responded to removal of the lemma and palea or to leaching with water. The time taken for accessions to 'panicle peep' was positively correlated (r = 0.83) with the length of the rainy winters of the sites of collection. The results show great brome has adapted genetically to the climate of southern Australia. Cropping systems that exploit the lack of residual dormancy and the potential for rapid and complete germination s