Time of sowing and cultivar effects on hardseededness and germination of subterranean clover seeds

The annual regeneration from seeds of subterranean clover plants after initial sowing depends on the hardseededness (HSmax, %), its breakdown rate (HSbreak, %/ degrees C) and the germinability of the seeds over time. Hardseededness is a physical mechanism of dormancy that prevents germination of seeds and is ecologically important for the persistence of subterranean clover in a range of environments. The effects of genotype (G) and sowing time (environment, E) on hardseedednes and germination were investigated for 'Antas', 'Denmark', 'Leura', 'Monti', 'Narrikup' and 'Woogenellup' harvested from six different sowing dates (June 2015-March 2016) in a field experiment in Canterbury, New Zealand. 'Antas' had a lower HSmax (53%) than 'Monti' (86%). HSbreak was affected by the G x E interaction with a doubling of HSbreak from 0.011%/degrees C for the June sowing date to similar to 0.02%/degrees Cd for the February sowing date for 'Denmark', 'Leura', 'Monti' and 'Narrikup'. There was less sensitivity of 'Antas' and 'Wogenellup' to sowing time. There was an increase in the percentage of abnormal seedlings as the sowing date advanced from winter to late-summer. The developed parameters enabled estimation of seedling emergence and indicate cultivars which have a competitive advantage of an early seedling regeneration in temperate regions.