Germination and Priming of Tomato, Carrot, Onion, and Sorghum Seeds in a Range of Osmotica

Abstract

Abstract Germination responses of tomato, carrot, onion, and sorghum seeds to solutions of K2HPO4, K2HPO4 + KNO3, KNO3, K3PO4, K3PO4 + KNO3, and polyethylene glycol (PEG) 6000 at osmotic potentials between −0.25 and −1.75 MPa at 15°C were studied. Seeds that did not germinate in solutions subsequently were germinated in H2O to evaluate the efficacy of priming. Germination was more closely related to ionic strength than to osmotic potential of the imbibitional solution. Carrot seeds germinated in all salt solutions up to an ionic strength of 0.8 mol ions/liter, while onion and sorghum seeds had a threshold of about 1.0 mol ions/liter in salt solutions, except in K3PO4, which had a reduced threshold for both species. Tomato seeds, however, showed a wide range of thresholds between osmotica. The species also differed in their responses to individual osmotica. Differences in effect of osmotica for one germination parameter were not consistent for all germination parameters. Salt solution priming of tomato and carrot seeds was more beneficial to subsequent germination than PEG priming. Salt solution priming of onion seeds was less beneficial than PEG priming, while salt solutions were toxic to sorghum seeds. Tomato and carrot seeds primed in solutions that contained KNO3 had much shorter time spreads of germination than those primed in solutions without KNO3. The use of priming solutions of osmotic potential lower than that needed to inhibit germination resulted in underpriming of the seeds, which could cause a time spread of germination longer than that of untreated seeds. The presence of KNO3 in the priming solution was shown to alleviate some of the disadvantages of underpriming.