Dormancy and hard-seededness in Western Australian serradella (Ornithopus compressus L.)

Abstract

Experiments were carried out to test the effects of harvesting date, relative humidity in storage, alternating high and low storage temperatures, and hulling and scarification on seed permeability, dormancy, and viability in Western Australian serradella (Ornithopus compressus L.).

Hard-seededness (permeability) was found to be governed by seed moisture content. At storage humidities of 76% R.H. and more, all initially soft seeds remained soft, while at 44% R.H. or less and in the open laboratory, all seeds became fully hard. Storage at 52 and 66% R.H. resulted in semi-hardness and delayed germination. Seed maturity did not influence the degree of hardness attained.

Seeds in the field became impermeable as soon as they were mature. Breakdown of impermeability occurred either naturally in the field or in storage under alternating temperatures simulating the summer temperature range at the soil surface, but not in storage at a constant temperature of 20°C. The presence of husks surrounding the seeds had no appreciable effect on permeability.

The viability of soft seeds was impaired after 7 months' storage at R.H. levels of 76% and over and a constant temperature of 20°C. Hard-seededness gave complete protection against the injurious effects of these conditions. Loss of viability of the soft seeds was not related to their maturity within the range of maturities tested.

No physiological dormancy was observed in the seeds themselves, but unhulled seeds (i.e. those not threshed out of the pod segments) tended to remain dormant, which suggested the presence of a water-soluble germination-inhibiting substance in the husks. This dormancy broke down in mature pod segments under alternating high and low temperatures, but not in immature segments or at a constant temperature of 20°C.

Recommendations are made for improving the germination of commercial Western Australian serradella seed.