The efficiency of prechilling and gibberellic acid (GA3) for breaking thermodormancy in lettuce

Abstract: The study focused on increasing the germination of lettuce cultivars under high-temperature conditions by seed treatments. The seeds of lettuce cultivars Yedikule, Iceberg, Iri Kıvırcık, and BT Iri Kıvırcık with different leaf morphology were primed by different doses of gibberellic acid (GA3) (0, 250, 500, and 1000 ppm) and preconditioned by chilling and heating. The seeds were germinated at optimal (20 °C) and high (35 °C) temperatures. The results showed that high temperature adversely influenced the germination percentage of lettuce cultivars. The mean germination percentage was 16.8% at 35 °C and 93.4% at 20 °C. Also, there was a significant difference among lettuce cultivars for germination at 35 °C. Iri Kıvırcık and BT Iri Kıvırcık showed a severe thermodormancy and hardly ever germinated at 35 °C. Prechilling and preheating promoted germination at 35 °C compared to unprimed seeds, but prechilling resulted in higher germination than preheating. GA3 was found to be the most useful treatment for improving germination compared to the others. The germination percentage of Iceberg, Yedikule, and Iri Kıvırcık primed with GA3 doses reached over 80%. The results suggested that the germination performance of lettuce cultivars suffering from thermodormancy or wherever climatic conditions with high temperatures should be promoted by the application of 500 ppm de GA3.