Induced Thermo-dormancy in Rapeseed (Brassica napus L.) Cultivars by Sub- and Supra-optimal Temperatures

Abstract

Till now the impacts of sub- and supra-optimal temperatures on the induction of secondary dormancy (SD) in rapeseed seeds have not yet been investigated. Therefore, the possibility of SD induction at sub- and supra-optimal temperatures (thermo-dormancy) was investigated in six rapeseed cultivars with high (Trapper and Agamax), medium (Hayola-50 and Hayola-420) and low (Rohan and Zarfam) SD potential. Seeds were incubated at 5, 10, 15, 20, 25, 30, 35, 37 and 40 °C under both light (12 h light/12 h dark) and continuous dark conditions to assess for thermo-dormancy induction. Thermo-dormancy in high SD potential cultivars was more than 90% at 5, 37 and 40 °C in the dark. The cultivars with medium SD potential only displayed high level of thermo-dormancy (> 70%) at 37 and 40 °C, but at 5 °C it was less than 25% in the dark. In high and medium SD cultivars, light stimulated germination and reduced thermo-dormant seeds at sub- and supra-optimal temperatures. In the low SD cultivars, which displayed very low percentages of thermo-dormancy and thermo-inhibition of germination at sub- and supra-optimal temperatures, seed mortality increased with rise of temperature. Accordingly, the reduced germination of rapeseed at sub- and supra-optimal temperatures may be due to thermo-inhibition, thermo-dormancy and seed mortality, which are also affected by light condition. Use of seeds with low potential for SD induction from tolerant cultivars in environments prone to temperature stress and/or adopting suitable planting date to increase crop establishment under stressful environments are recommended.