Overcoming physiological dormancy in seeds of Triodia (Poaceae) to improve restoration in the arid zone

Reinstating dominant Triodia grassland communities following disturbance has been a focus of arid land restoration practitioners for decades in Australia. Yet, seed quality and variable seed germination have seriously hindered the reestablishment potential of Triodia species to date. This study set out to examine diaspore quality, germination requirements, and seed dormancy in seven Triodia species to identify first, then resolve, germination impediments. Freshly collected florets from all species were cleaned to ensure that each floret contained a viable seed and then evaluated for their initial germination capacity. Very low germination from florets (<10%) indicated the presence of physiological seed dormancy (PD) in all species. However, germination was significantly improved (up to 57%) with the use of 0.67 mu m karrikinolide (KAR(1)), and to a lesser degree with 289 mu m gibberellic acid (GA(3)). When the covering floret structures (i.e. lemma and palea) were removed, germination increased up to 59%, which was further enhanced after exposure to GA(3) (up to 66%) and KAR(1) (up to 92%). Optimal germination temperatures varied from 20 to 35 degrees C and were species specific. Dry after-ripening (DAR -30 degrees C and 50% relative humidity [RH]) of florets and seeds promoted the progressive loss of PD over 12-24 months storage for most species. Germination, dormancy level, and response to incubation temperature differed amongst species, experimental units (florets and seeds), DAR treatments, and after exposure to germination stimulants (GA(3) and KAR(1)). For use in restoration seeding programs, careful consideration of seed pre-treatments is necessary to improve germination in Triodia species.