The priming of seeds: investigations into a method of priming large quantities of seeds using salt solutions

Seed priming, which involves the hydration of seeds in an osmotic solution before sowing, produces seeds with improved germination performance. This study was aimed at optimizing the priming of tomato, carrot, onion and sorghum seeds by a method which could be readily scaled up for commercial use. -- Initially, to determine appropriate priming solutions, the germination responses of the four species to a range of osmotic potentials from 0 to -1.75 MPa in a range of osmotica - K₂HPO₄, K₃P0₄, KN0₃, K₂HPO₄ + KN0₃, K₃P0₄ + KN0₃ and Polyethylene glycol (PEG) - were investigated. -- The most effective priming treatment was shown to be one in which the osmoticum prevented germination without being toxi c, at a high osmotic potential. There were marked interactions between species, osmotic potential and the osmoticum used for priming. Tomato seeds were readily primed in any of the series of salt or PEG solutions . All of the solutions tried were adequate for carrot seeds. Onion seeds could be primed in either K₂HPO₄, K₃P0₄ or PEG solutions; however, all solutions were toxic to sorghum seeds or failed to prevent germination. -- The selected priming treatment was further optimized by experiments that investigated the influence of duration and temperature of priming. Priming at a lower temperature for a longer time was more beneficial than at higher temperatures. However, priming for too long a period was found to have adverse effects . Tomato seeds showed improved performance after priming for 16 t o 18 days at 15 C whereas for carrot seeds a duration of 8 to 10 days was adequate, but prolonged treatment led to reduced germination percentages. Columns of aerated solutions were found to be suitable for the priming of large quantities of tomato and carrot seeds. Air-drying of primed tomato and carrot seeds was possible without loss of germinability or priming effect. -- Limited field experiments at Yanco Agricultural Research Centre showed that primed tomato and carrot seeds emerged twice as fast as untreated seeds and had improved uniformity of emergence, particularly at low soil temperatures. These benefits from priming were maintained through to the first true leaf stage of development. -- It was concluded that it was possible to prime certain seeds in simple salt solutions by a method capable of expansion to commercial scales of operation and produce benefits to emergence which were maintained after drying to facilitate sowing using existing drilling equipment.