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The annual regeneration from seeds of subterranean clover plants after initial sowing depends on the hardseededness (HSmax, %), its breakdown rate (HSbreak, %/ °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%/°C for the June sowing date to ∼0.02%/°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. [ABSTRACT FROM AUTHOR]

In vitro germination tests were performed at 11 constant temperatures (range 2.5–35°C) to quantify the maximum germination percentage and germination rate of four subterranean clover cultivars ('Antas', 'Denmark', 'Monti' and 'Narrikup'). These were used to estimate their cardinal temperatures, base (Tb), optimum (Topt) and maximum (Tmax) and the thermal time requirements for seed germination. Germination percentages were ≥ 88% in the 5–25°C temperature range for all cultivars. The time to reach 50% of final germination (T50) decreased from 12 to 2 days as the temperature increased from 2.5 to 17.5°C. The determined Topt were 16°C for 'Monti' and 'Narrikup' and 22°C for 'Antas' and 'Denmark'. At a common Tb of 0°C the thermal time requirements for T50 were 32 ± 1°Cd for 'Antas' and 'Denmark' and 39 ± 1°Cd for 'Narrikup' and 'Monti'. 'Antas' and 'Denmark' (both from Italy) germinated at the widest range of temperatures. [ABSTRACT FROM AUTHOR]