Growth regulators restore germination of Orobanche seeds that are conditioned under water stress and suboptimal temperature

Broomrapes (Orobanche spp.) are serious root parasitic weeds that cause great damage to crop production in many parts of the world. The study focussed on the influence of plant growth regulators on germination of Orobanche seeds conditioned under suboptimal temperature (at 13°C) and under water stress (at –1 and –2 MPa). Three widely distributed species of broomrapes (O. aegyptiaca, O. ramosa, and O. minor) were used in the experiments. Exogenous GA3 (10 mg/L), brassinolide (1 mg/L), and fluridone (10 mg/L) significantly increased the broomrape seed response to the germination stimulant GR24 (10–6 m) even when seeds were first conditioned at a suboptimal temperature and under water stress. The highest germination was obtained when the combined treatments with fluridone and brassinolide, or with GA3 and brassinolide were applied together with the germination stimulant. This indicates that there were additive effects among various plant growth regulators in the regulation of germination response in Orobanche seeds. With the prolongation of conditioning periods under low temperature stress, the restoration capacities of seed germination by a single growth regulator decreased, but the combined treatments of growth regulators retained their positive effects in restoring seed germination.