Dormancy determination of T nodosa

Mature seeds of T. nodosa were collected from a commercial pyrethrum field in February 2002. Seed viability, as determined by a TZ test (ISTA, 1996), was 96%. Moistened seeds of T. nodosa were stored at 4°C for 0, 1, 2, 3, 4, 6, 8, 12 and 16 weeks with a 12 h light/dark photoperiod. Following stratification treatment, seeds were transferred to a constant temperature of 20°C with a 12 h light/dark pho-toperiod. Seeds were also kept in complete darkness for the prechilling treatment of 0, 2, 4, 8 and 16 weeks and following transfer to 20°C, by applying a double wrapping of reflective aluminium foil around each Petri dish. Seeds incubated in light were counted every 7 days following placement at 20°C for 28 days and germinated seeds were recorded and removed. Seeds incubated in complete darkness were counted only once after incubation at 20°C for 21 days.

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