The softening of hard seeds of san-plain lupin (Lupinus varius)

Abstract

Two types of impermeability were found in hard seeds of sand-plain lupin. Hard seeds with a moisture content above 10% (dry weight basis) are conditionally hard. They soften slowly when placed in a humid atmosphere or moist soil, the rate of softening varying directly with the moisture content. Moisture penetration occurs at random sites over the testa, but not normally at the hilum or strophiole. Hard seeds with a moisture content below 8.5%, on the other hand, are absolutely hard, and will not soften as a result of exposure to moist conditions. They will soften, however, if exposed to daily temperature fluctuations between 15 and 65°C, which fracture the impermeable coat at the strophiole. This type of softening does not occur in seeds with a moisture content above 8.5%. It is concluded that under field conditions the autumn germination pattern of the species, which has no physiological seed dormancy, would depend on the degree to which the seeds become desiccated during the summer. Where moisture contents remain above l0%, the seeds would give a scattered germination over several months. With moisture contents below 8.5% the only seeds capable of germinating would be those with a fracture at the strophiole resulting from summer temperature fluctuations. These would all germinate within a few days following moistening of the soil.