Responses of tomato seeds to osmoconditioning as related to temperature and oxygen

Abstract

AbstractUntreated (control) tomato seeds germinated at temperatures ranging from 15 to 35°C. There was a positive linear relationship between the rate of germination (expressed as the reciprocal of time to obtain 50% germination) and temperature up to the thermal optimum. At higher temperatures, the negative relationship was also linear. The thermal optimum for seed germination was 27–28°C and the lower and maximal temperatures were around 9 and 40°C, respectively. Germination was strongly reduced in atmospheres containing less than 10% oxygen. After pretreatment at 15°C in a polyethylene glycol-8000 solution at –1.0 MPa, seeds germinated faster in a wider range of temperatures, and this stimulatory effect remained after drying back the seeds. Such a pretreatment did not change the optimal and maximal temperatures of germination, but decreased the lower temperature to about 6°C. The beneficial effect of osmoconditioning increased as the duration of the treatment increased and was maximal after 5–7 days. Osmotic pretreatment also reduced the sensitivity of seeds to oxygen deprivation; 50% of the seeds germinated within 7 days in 5% oxygen. The range of temperatures and the concentrations of oxygen which were effective in osmoconditioning were very similar to those which allowed the germination of untreated seeds. In particular, the optimal temperature (27–28°C) and oxygen concentrations (more than 10%) for osmoconditioning and germination were the same. These results confirm that the beneficial effect of osmotic pretreatment (priming) corresponds to the realization of germination sensu stricto (phase II of the germination process).