Dynamics of seed dormancy and germination at high temperature stress is affected by priming and phytohormones in rapeseed (Brassica napus L.).

High temperature stress (HTS) imposes secondary dormancy (SD) also known as thermo-dormancy in many seeds. Priming by soil moisture however, may improve germination though under HTS it may compromise seed longevity. Knowledge of how HTS and priming affect dormancy status/viability loss of a particular crop seed species is essential in agriculture. Accordingly, control non-primed and hydro-primed seeds from Dk-xpower and Traper rapeseed cultivars with low and high potential for SD induction, respectively, were compared for germination behavior, response to GA and some phytohormone effectors under HTS. HTS reduced germination in non-primed Dk-xpower and Traper seeds mainly through the induction of thermo-inhibition/death and thermo-dormancy, respectively. Under HTS, GA application reduced thermo-dormancy in favor of thermo-inhibition only in Traper but the GA inhibitor paclobutrazol intensified thermo-dormancy in both cultivars. The ABA inhibitor, fluridone also reduced thermo-dormancy in favor of thermo-inhibition only in Traper. Thus, under HTS, GA biosynthesis is determinant in seed thermo-dormancy/thermo-inhibition dynamics. Hydropriming improved germination under HTS through reduced thermo-inhibition/death (Dk-xpower) and thermo-dormancy (Traper). Here, GA application increased death and compromised germination mainly in Dk-xpower. Paclubutrazol application however, increased thermo-dormancy by compromising thermo-inhibition/death in Traper. Overall, hydro-priming weakened seed phytohormonal germination responses. Controlled deterioration resulted in decreased longevity of hydro-primed seeds but induced SD in non-primed Traper seeds. Thus, down-regulation of GA biosynthesis may control differential induction of SD in rapeseed seeds under HTS while hydro-priming stimulates seed germination possibly through overcoming limitations in GA biosynthesis. The agricultural importance of these findings at the ecosystem scale is discussed.