The effect of osmotic priming on onion (Allium cepa L.) seedling emergence was evaluated in the field and in a controlled environment at 15C. Seeds of onion cultivars Bronze Wonder, Challenger, Big Mac, and White Keeper were primed in a solution of 300 g polyethylene glycol 8000/liter for 7 days at 10C 1 to 2 weeks before being planted in Spring 1986 and Summer 1987. Time to 50% of maximum emergence (T) for seedlings from primed seeds averaged 10% to 12% less than for unprimed seeds in both seasons and in laboratory experiments. Maximum emergence was improved 7% by priming in one spring field experiment but not in the summer field experiments or in the laboratory. Differences in T among cultivars in the 1986 experiments were small and significant only in one laboratory experiment. In 1987, cultivar differences in T were significant but not consistent in all experiments. Cultivar T means from laboratory experiments were significantly (P = 0.05) correlated with those for field emergence in three of four experiments, but coefficients were low (r = 0.37 to r = 0.45). Values for maximum emergence in the laboratory were not correlated with maximum emergence in the field. Laboratory emergence tests at 15C were a poor predictor of field emergence. Seed priming may benefit establishment of spring-seeded onions emerging at soil temperatures ≤ 15C more than summer-seeded onions emerging in soils >24C.
Pregermination techniques of osmotic priming and hydropriming have been used to enhance seed performance on planting Osmotic priming and hydropriming method were compared on the basis of germination performance O2, N2 and air were supplied to 500 ml vessels containing seeds with distilled water or -1.31 MPa PEG solution for 10 days On removing seeds from vessels, seeds were dried back to original water content. There were no differences in total germination between osmotic priming and hydropriming treatments t50 was reduced dramatically from 112 to 32 hours, using hydropriming with air and N2supply for 1 day, compared to 70 hours of osmotic priming. Solute leakage from O2supply of both methods was higher than air or N treatment, Indicating the loss of membrane integrity Hydropriming with O2induced radicle emergence and loss of desiccation tolerance around 28 hours after treatment LEA protein levels were not changed in both treatments except for hydropriming with O2. The timing of desiccation tolerance loss was correlated with that of degradation of LEA protein. O2supply caused the adverse effects on seed performance from both methods 1 day after treatment
High germination seed lots of purple coneflower [Echinacea purpurea (L.) Moench] were evaluated for laboratory germination following osmotic priming or chilling stratification. Compared to nontreated seeds, osmotic priming at 25C in salts (KNO3 + K3PO4; 1:1, w/w) or polyethylene glycol 4000 (PEG) increased early (3-day) germination percentage at 27C of all seed lots, and improved total (10-day) germination percentage of low-germination seed lots. Total germination percentage was unaffected or increased by priming for 4 days compared to 8 days, and by priming at –1.0 MPa compared to –0.5 MPa (except for one low-germination seed lot). Chilling stratification in water at 5 or 10C increased early and total germination of all seed lots, except for that same lot, compared to nontreated seeds. Total germination percentage was unaffected or increased by stratification at 10C rather than at 5C. Neither extending stratification ≥20 days nor lowering osmotic potential with PEG during stratification improved total germination percentage.
Germination was evaluated in six seed lots of purple coneflower purchased from four different seed companies. Standard germination percent ranged from 28% to 90% depending on the seed lot. For seed collected in 1989, seed size and stage of development of the seed at harvest could not account for the wide variability in seed germination observed in the purchased seed lots. preconditioning the seed with either cold stratification (10°C for 10 days) or osmotic priming (PEG or salt solution at -5 bars for 5 days) increased the rate of germination and the overall percent germination for all seed lots and dramatically improved germination in the poor germinating seed lots. Preconditioning appears to overcome either a shallow physiological dormancy or compensates for seeds with poor vigor or quality. In either case, seed preconditioning drastically improved seed germination (rate and percent) in greenhouse and field tests for purple coneflower.
Priming, a controlled-hydration treatment followed by redrying, improves the germination and emergence of seeds from many species. We compared osmotic and matric priming to determine which was the most effective treatment for improving broccoli seed germination and to gain a greater understanding of how seed vigor is enhanced by priming. Broccoli (Brassica oleracea L. var. italica) seeds were osmotically primed in polyethylene glycol (PEG 8000) at -1.1 MPa or matrically primed in a ratio of 1.0 g seed:0.8 g synthetic calcium silicate (Micro-Cel E):1.8 ml water at -1.2 MPa. In the laboratory, germination rates and root lengths were recorded from 5 to 42C and 10 to 35C, respectively. Broccoli seeds germinated poorly at >35C. Root growth after germination was more sensitive to temperatures >30C and <15C than radicle emergence. Matric and osmotic priming increased germination rate in the laboratory, greenhouse, and field. However, matric priming had a greater effect on germination and root growth rates from 15 to 30C. Neither priming treatment affected minimum or maximum germination or root growth temperatures. Both priming treatments decreased the mean thermal time for germination by >35%. The greater germination performance of matrically primed seeds was most likely the result of increased oxygen availability during priming, increased seed Ca content, or improved membrane integrity.
Seeds of purple coneflower (Echinacea purpurea (L.) Moench were osmotically primed (OSP) in polyethylene glycol (PEG) or matrically primed in expanded vermiculite No. 5 (solid matrix priming, SMP). With both OSP or SHP at 15C, 10-day exposure to -0.4 MPa resulted in lowered time to 50% germination (T,) and higher germination percentage than shorter exposure (5-day) or lower water potential (-1.5 MPa). SMP- and OSP-seeds performed similarly in a greenhouse trial, resulting in 80% and 34% seedling emergence at 23C and 37C, respectively, compared to 58% and 27% for non-primed seeds. Seedling emergence rate and synchrony from primed seeds were greater than from non-primed seeds at both temperatures. An incubator study established that adding 10-4M GA3 and 10 mN ethephon (2-chloroethylphosphonic acid) to the PEG or vermiculite resulted in lower T50 and higher germination percentage than priming without these growth regulators. A further incubator study established that less-expensive trade products (Pro-Gibb Pius 2X) and Florel could substitute for the reagent-grade growth regulators. Seeds primed in PEG or vermiculite containing 10-4M GA3 from Pro-Gibb Plus 2X and 10 mM ethephon from Floral had lower T50 and higher percentage emergence in a greenhouse trial than seeds primed without growth regulators. Compared to the non-primed seeds, these treated seeds had 29% greater seedling emergence and 61% less time to 50% emergence.
Lettuce (Lactuca sativa L. ‘Empire’) seeds (achenes) were primed in aerated solutions of polyethylene glycol 8000 (−1.56 MPa) for 24 hr at 18°C and dried to 6% water content. Control (untreated) and primed seeds then were commercially coated in a clay-based material (Royal Sluis Splitkote). Priming prevented the occurrence of thermodormancy in seeds imbibed at temperatures between 32° and 37° and accelerated the rate of germination at all temperatures tested. Coating delayed germination slightly and reduced the maximum germination temperature of control seeds. Primed seeds exhibited thermodormancy when tested immediately after coating, but they soon regained their capacity for high-temperature germination. When tested after 5 months of storage at 5°, primed seeds germinated at temperatures up to 37° regardless of coating. Osmotically primed seeds retained the capacity for germination at high temperature after seed coating and storage, providing an effective means of improving stand establishment of direct-seeded lettuce in hot weather.
Osmotic priming of seed was evaluated as a means of improving stand establishment, early seedling growth, and yield of processing tomatoes (Lycopersicon esculentum Mill. cvs. UC204 and 6203). Seeds were primed in aerated solutions of 3% KNO3 (w/v) or of polyethylene glycol 8000 (PEG) of equivalent osmotic potential (-1.25 MPa; 314 g-kg−1 of water) at 20°C for 7 days, rinsed, and dried in forced air at 30°. Under laboratory conditions, seeds primed in either osmoticum germinated more rapidly than untreated seeds at 20° and 30°. At 10°, the PEG treatment was of little benefit for either variety, while the KN03 treatment still reduced the time to 50% germination to 60% to 80% of the control value. Priming did not affect the final germination percentage. Seedling emergence in the field was evaluated in March and April planting dates. In both trials, seedlings from primed seeds emerged earlier and more uniformly than seedlings from untreated seeds. Seedlings from primed seeds maintained greater mean plant dry weights, leaf areas, and ground cover percentages than untreated seedlings throughout the preflowering period. This advantage was due entirely to early emergence rather than to an increased relative growth rate. The early growth advantage from seed priming did not improve earliness of maturity, total yield, or soluble solids content of fruit.
For annual crops, the time from planting to seedling establishment is a crucial phase in the production cycle. Uniformity and percentage of emergence of direct-seeded crops can have a major impact on final yield and quality, particularly for vegetables (84). Techniques of precision planting to achieve desired plant populations depend on a high probability of successful establishment for each seed planted (26). Furthermore, increasing use of expensive hybrid seed has placed additional emphasis on the performance of each seed planted. The soil environment often, however, is not conducive to rapid germination and seedling growth. Physical stresses, such as extreme temperatures, excess or deficit of water, salinity, or soil crusting; and biological stresses, including pathogens and insects, can all adversely affect germination and seedling growth. These problems are compounded by the increased susceptibility of plants to many of these stresses during germination and emergence. It is not surprising, therefore, that there have been many attempts to devise presowing treatments to improve seed performance in the field. The wide range of such treatments has been thoroughly reviewed and categorized by Heydecker and Coolbear (38).
Commercially processed citrus seeds of Carrizo citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliata (L) Raf.], Swingle citrumelo (C. paradisi Macf. × P. trifoliata), Cleopatra mandarin (C. reticulate Blanco), and sour orange (C. aurantium L.) were used to test the effects of grading, hydrating, and priming on the rate of germination and seedling emergence. Sorting seed into groups by fresh weight or diameter did not generally improve seed performance. Seed fresh weight was highly correlated with maximum seed diameter; also, large seed weight and size were associated with a larger number of embryos. When seedlings from the extra embryos were removed, large seed produced the largest seedlings. Soaking seeds in aerated water significantly increased germination and emergence rates over unsoaked seeds. Soaking at 35C rather than 25C enhanced these differences. Priming seeds in one of three solutions of polyethylene glycol 6000 (—0.6 to—1.2 Mpa) was not successful> as germination and emergence Per centages were lower than in distilled water.