Thermal time requirements for germination of four subterranean clover cultivars.

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]