Accelerated Germination of Pepper Seed by Priming with Salt Solutions and Water

Sweet pepper (Capsicum annuum L. CV. Keystone Resistant Giant #3) seeds were imbibed (primed) in salt solutions to determine a) what concentrations would inhibit radicle emergence and b) the influence this delay in radicle emergence would have on subsequent germination. Seeds were primed for 17 days at 23C in petri dishes with KNO3, KCl, NaCl, K2SO4, Na2SO4, 1 NaCl: 1 CaCl2 (mol/mol), Ca(NO3)2, CaCl2, Na2HPO4, and K2HPO4 in 10, 25, 50, 100, 200, or 300 mM of the salts. Germination was not inhibited in the 10to 100-mM salt range, although most 200and all 300-mM solutions reduced radicle emergence to <5.0%. The time to 50% germination (T50) of these primed seeds in water significantly (P < 0.01) decreased, when compared to unprimed seeds, and a negative correlation (r = – 0.98) was observed between this reduction and the osmotic potential of the solutions. Solutions with the highest osmotic potentials most severely reduced T50 without reducing the final germination percentage. For seeds primed in K2SO4 or Na2SO4 (200 and 300 mM) through 18 days, the reduction in T50 and duration of priming were negatively correlated (r = 0.99). Seeds soaked in double distilled water and then dried germinated faster than controls, but not as fast as seeds primed in salt solutions. Priming of pepper seeds in this study was dependent on the osmotic potential of the solution, rather than a specific salt, and the duration of treatment. Table 1. Time to 50% germination (T50) and final germination percentage (FGP) of pepper seeds after priming for 17 days in a variety of salts. Treatments lacking T50 values were those in which seeds germinated during the priming treatment. Osmoconditioning (priming) to enhance the rate and the uniformity of germination has been studied extensively (Bradford, 1986; Heydecker and Coolbear, 1977; Heydecker and Gibbins, 1978; Heydecker et al., 1973). Both ionic and nonionic compounds have been effectively used as priming agents (Bradford, 1986). Two fundamental concepts associated with seed priming are not clearly defined. First, when priming with salts, does the effectiveness of the solution depend on the osmotic potential or the salt species used? Nerson and Govers (1986) suggested that nitrate-containing compounds may function more efficiently than other salts as priming agents, whereas Levitt and Harem (1943) found several salts to be effective for priming. However, in both studies, the osmotic potentials of the salt solutions were not equilibrated. Haigh and Barlow (1987) found that KNO3 was beneficial in decreasing the germination spread for seeds of several species, although the osmotic potential of the solution was a Received for publication 9 May 1990. Texas Experiment Journal Article no. 23334. Use of a company or product name does not imply approval or recommendation of the product to the exclusion of others which may also be suitable. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1Present address: USDA, Agricultural Research Service, Northern Region Research, Seed Biosynthesis Research Unit, 1815 N. University, Peoria, IL 61604. 2To whom reprint requests should be addressed. HORTSCIENCE, VOL. 26(4), APRIL 1991 key component to effective priming. When priming with nonionic compounds (PEG), several workers (Atherton and Farooque, 1983; Bodsworth and Bewley, 1981) have reported that the solution’s osmotic potential is an essential factor in effective priming. Second, what influence does the duration of priming have on the overall process? Priming intervals are critical to achieving maximum efficiency of the method (Atherton and Farooque, 1983; Bodsworth and Bewley, 1981; Ely and Heydecker, 1981; Heydecker et al., 1973; Khan et al., 1980/ 81; O’Sullivan and Bouw, 1984). Bodsworth and Bewley (1981) demonstrated a time dependence in priming with PEG. However, a detailed study with many salt solutions over a wide osmotic range has not been presented. Our research was designed to determine if: 1) effective priming could be achieved with a wide variety of salts without a reduction in the overall germination, 2) the rate of germination after priming depends on a specific salt or the osmotic potential of the priming solution, and 3) the duration of the priming treatments was important and whether prolonged exposures to high salt concentrations would reduce the final germination percentage. Sweet pepper seeds (from the same seed lot) were used for all germination and priming experiments in this study and all were performed with petri dishes in a Lunaire environmental chamber (Percival Manufacturing Co., Boone, Iowa) in darkness at 23C. Potassium nitrate, KCl, NaCl, K2SO4, N a2S O4, 1 NaCl : 1CaCl2 (mol/mol), Ca(NO3)2, CaCl2, Na2HPO4, and K2HPO4 solutions at six concentrations (10, 25, 50, 100, 200, and 300 mM) were used to determine which ones could prevent radicle emergence for 17 days. All solutions were initially adjusted to pH 7.0 (with HCl), and the osmotic potential of each solution was determined with a Wescor 5100C Vapor Pressure Osmometer at 23C (Wescor, Logan, Utah). Petri dishes (60 × 15 mm) containing two pieces of filter paper (#2, Micro Filtration Systems, Dublin, Calif.) were used. Fifty seeds were weighed and placed in each petri dish, with three dishes (replicates) per treatment. A sufficient volume (3.5 ml) of each solution was added to partially submerge the seeds. Radicle emergence was checked daily, and germination was defined as radicle emergence of ≥2 mm. Salt solutions were changed every 2 days by flooding the petri dish with 10 ml of the respective solution, immediately aspirating away all liquid, and adding back 3.5 ml of priming solution. The priming solutions were changed to maintain a constant osmotic potential of the solutions. Germinated seeds were removed from the petri dishes and discarded, Seeds were removed after 17 days from solutions where <5% of the radicles had emerged. These seeds were rinsed thoroughly with double distilled water (DDH2O) to remove the external salts, placed on paper towels on the laboratory bench, and dried to the original weight under ambient conditions (23C); drying time in all cases was ≈24 h. Seed weights were measured before and after priming. The steps noted will be referred to as seed harvesting. Primed seeds were germinated at 23C with DDH2O in petri dishes. Seed treatments were evaluated by time to 50% of final germination (T50) and the final germination percent-