Patterns of change in seed dormancy and persistence of Bromus diandrus Roth. (great brome) in the field

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Abstract
Mature seeds of great brome (Bromus diandrus Roth.) from Western Australia were dormant when freshly harvested. This dormancy was lost progressively over summer. The rate of loss of dormancy was more rapid in the northern than in the southern accessions. Compared with bare soil, a wheat stubble microenvironment favoured the relief of dormancy during the initial period of dormancy breakdown. Shallow burial of newly shed dormant seeds also accelerated the after-ripening process. Germination of non-dormant seeds during summer was minimised by high temperatures and low soil moisture content. By autumn/winter, almost all the seeds became germinable. At 20/10.degree. C, the temperature regime corresponding to late autumn, 95-99% germination occurred under constat darkness, but in the light germination varied from 55 to 95%. In the field, complete mass germination did not occur but germination was a well-defined event. There was little germination following this pulse until the succeeding autumn/winter. The seed bank of great brome appears to be essentially a transient one, but this is the subject of further work. The concentration of germination at a single time of year, and the very small carryover of seeds to successive years, suggest that good control should be achieved by a single, timely cultivation or spraying.