Need for High-quality Seed for Effective Priming to Overcome Thermodormancy in Lettuce

Abstract

Priming has been used to circumvent thermodormancy in lettuce seeds, but results have sometimes varied according to cultivar and seed lot. Two- and 3-year-old seeds of ‘Montello’ and ‘Green Lakes’ lettuce (Lactuca sativa L.) were aged at 41°C and 100% RH for 2, 3, or 5 days, dried, then primed for 20 hours at 15° in aerated 1% K3PO4 and redried at 7° and 45% RH. Germination at 25° was not affected by 2 and 3 days of accelerated aging or by priming of 2- and 3-year-old seeds. After 5 days of accelerated aging, germination decreased for both primed and nonprimed seeds. No germination occurred at 35° unless the seeds were primed. Natural aging led to a reduction in germination of primed ‘Green Lakes’ seeds at 35°. All accelerated aging treatments led to reduced germination of the primed seeds at 35°, regardless of cultivar. After prolonged accelerated aging (3 or 5 days), priming did not overcome thermodormancy. Accelerated aging greatly reduced germination rate at 25°. Priming for longer durations of 35 and 40 hours, after 3 days of accelerated aging, increased germination rates slightly at 25° but did not improve germination patterns at 35°. Only lettuce seeds of the highest quality could be effectively primed to overcome thermodormancy.