Seed dormancy of Emex australis and E. spinosa

Seed dormancy in Emex australis and E. spinosa was investigated by the application of light, gibberellic acid (GA3) or kinetin (KT) and by scarification of the fruits. Results from these experiments suggested that dormancy was controlled by the balance between promotive hormones and inhibitors and that a semipermeable barrier prevented leaching of inhibitors and/or uptake of exogenously applied GA3 or KT, and/or restricted oxygen diffusion. Storage of seed at alternating temperatures in the laboratory or the field reduced the level of dormancy, the reduction being more rapid for E. australis than for E. spinosa. The degree of dormancy also varied between populations within E. australis. Burial of non-dormant seeds of E. australis did not induce secondary dormancy even though dormancy was enforced by burial at a temperature regime of 25/20°C. Partly dormant (light-requiring) seeds of E. spinosa attained a degree of secondary dormancy following burial for 4 weeks at 25/20° and 9/9°. The results are discussed with reference to cultural control practices.