EFFECTS OF SEED OSMOPRIMING ON GERMINATION OF TOMATO AT DIFFERENT WATER POTENTIAL

Osmotic priming of seed was evaluated as a means of improving germination performance of the tomato (Lycoperiscon esculentum Mill. cvs. Rio fuego and Sunny) under six levels of water potential of the germination medium (0, -0.5, -0.7, -0.9, -1.1 and -1.3 MPa) maintained by solutions of polyethylene glycol (PEG) 6000. Seeds were primed in aerated solutions of equivalent osmotic potentials (-1.5 MPa) of PEG (for 6 or 8 d) or of KNO3+K3PO4 (for 4, 6 or 8 d) at 20+/-1 degrees C and then rinsed, and dried. Seed osmopriming increased ger mination percentage at low water potentials of the medium whereas the germination of untreated seeds was greatly inhibited. At -0.7 MPa the increase in germination percentage, compared to the control, determined by osmopriming ranged between 13% (priming in PEG for 8 d) and 40% (priming in KNO3+K3PO4 for 8d). At -1.1 MPa only KNO3+K3PO4 salt treatments improved germination. Priming in KNO3+K3PO4 for 6 or 8 d significantly improved final percentage of germination in both cultivars, in KNO3+K3PO4 for 4 d only in 'Sunny', in PEG only in 'Rio fuego'. Osmopriming, except that with PEG for 6 d, significantly reduced the mean time of germination (MTG) under all water potentials (optimal and sub-optimal). On average, the most effective treatment (KNO3+K3PO4 for 8 d) reduced MTG by about 4 days as compared to that of the control where it was 9.5 days.