PRIMING RESPONSES OF LEEK (ALLIUM-PORRUM L) SEEDS TO DIFFERENT DISSOLVED-OXYGEN LEVELS IN THE OSMOTICUM

Leek seeds (Allium porrum L.) cv. Winterreuzen were treated for 5 days in stirred bioreactors containing a -1.0 MPa polyethylene glycol (PEG 6000) solution. The level of dissolved oxygen was controlled from zer o to approximately two and a half times that of saturation with respec t to atmospheric air by bubbling through O2/N2 gas blends from 0% 02 t o 50% O2. The treatment with 0% O2 (i.e. bubbling with N2) gave no red uction in germination time compared to untreated seeds after allowing for the time for water imbibition. As the proportion of oxygen was inc reased, a rapid reduction was observed until a concentration equivalen t to air was used. Further increases to the maximum, produced only a m arginal further improvement. The reduction in germination times for se eds that had been cabinet dried was longer for all treatments due to t he time required for re-imbibition of water but the general response t o priming was the same as with undried seeds. Only dried seeds treated with air or higher oxygen concentrations showed enhanced synchronicit y of germination times. The percentage germination of seeds from all t reatments was the same, including the treatment with nitrogen gas. The se tests help to explain the recently reported advantages of using enr iched air for seed priming and are one of the necessary protocols for ensuring satisfactory bulk priming.