Interactions between seed priming treatments and nine seed lots of carrot, celery and onion. II. Seedling emergence and plant growth

Samples of three seed lots of each of three cultivars of carrot, celery and onion were primed in polyethylene glycol solution for two weeks at 15 °C. Seedling emergence was recorded in the field for carrot and onion and in the glasshouse for celery. Compared to the untreated control, priming increased the percentage seedling emergence in certain poorly-emerging seed lots of carrot and celery, but had no effect on onion. Mean emergence times were reduced by priming in all seed lots, by 3–5, 5–8 and 3–9 days in carrot, celery and onion respectively. The largest effects occurred in the slowest-emerging seed lots. There were significant interactions between priming and seed lots within cultivars in carrot and celery and between priming and cultivars in celery and onion. Priming generally reduced the spread of emergence times, but the effects were not statistically significant in carrot. Drying back the primed seeds had no effect on percentage emergence in onion, but reduced it (compared to primed seed which had not been dried-back) in certain carrot and celery seed lots. Primed and dried-back seeds emerged later than primed seeds, by up to 1·5, 2·6 and 2·6 days in carrot, celery and onion respectively. The spread of emergence times was generally larger for primed and dried-back seeds than for primed seeds, but the differences were not always statistically significant. Plant fresh weights were recorded 9, 7 and 12 wk after sowing for carrot, celery and onion, respectively. In each species, mean plant weight was inversely related to seedling emergence time; thus plants grown from primed seed were always heavier than the controls, by up to 33%, 182% and 47% in carrot, celery and onion respectively.     

Effects of osmotic priming and ageing on the germination and emergence of carrot and leek seed

Carrot and leek seed was osmotically primed in polyethylene glycol solution (273 g/kg water and 342 g/kg water respectively) for 10, 14 or 17 days before accelerated ageing for 0, 24, 48, 72 or 96 h. Priming reduced the germination time compared with non-primed seed. Accelerated ageing increased germination and emergence times and decreased percentage germination and emergence to a greater extent for the primed seeds than for non-primed seeds in both species. Primed and dried but non-aged seed from both species was stored at 10°C for 12 months. There was no loss of viability and improvements in germination time due to priming were maintained throughout the storage period for all the priming treatments in leek, and for the 10 and 14 day priming treatments in carrot. Carrot seed primed for 17 days lost some viability after 12 months storage compared with non-stored seed.     

Effects of osmotic priming and ageing on onion seed germination

Onion seeds were osmotically primed in polyethylene glycol solution (342 g/kg water) either for 14 days before accelerated ageing at 40°C. 18% m.c. for 0, 24, 48, 72 or 96 h, or for 10, 14 or 17 days after ageing. Priming improved the rate of germination compared with non-primed seed. Priming before ageing delayed the loss of viability due to ageing, but priming after ageing had no effect on viability. Primed and dried onion seed was stored for 18 months at 10°C, 9% m.c. with no effect on viability; improvements in germination rate due to priming were maintained over the storage period. Conductivity measurements of seed leachates were not a consistently reliable indicator of germination performance.     

The effects of re-use of polyethylene glycol priming osmotica upon the development of microbial populations and germination of leeks and carrots

Three batches of leek seeds were osmotically primed successively in the same polyethylene glycol solution in a bubble column at a seed concentration of 100 g/litre for seven days at 15°C. Three batches of carrot seeds were similarly primed in a separate solution for six days at 15°C. The concentration of microorganisms in the solutions increased rapidly during priming of the first seed batch for both seed types, but increases during priming of the second and third batches were small. The seeds were the main source of the microorganisms; priming reduced the numbers of colonies of filamentous fungi and increased those of bacteria and yeasts. The priming treatments improved the percentage germination of the three seed batches of primed carrots and reduced the mean time to germination in both species and the mean time to emergence in compost. Percentage emergence was not affected by priming except in the third batch of primed carrot seed. The presence of large numbers of microorganisms in the priming solutions did not greatly affect seed performance when the same osmoticum was used three times with leeks and twice with carrots. Priming did not affect the number of abnormal seedlings.     

Effects of combining priming and plant growth regulator treatments on the synchronisation of carrot seed germination

Osmotic priming of carrot seeds for 2 wk in polyethylene glycol (PEG, — 10 MPa) at 15 °C led to more rapid and synchronous germination at 20 °C compared to untreated seeds. These responses were enhanced by a 24 h pre-priming soak in water or a change of solution after the first 24 h of priming to remove leachate. The inclusion of 200 mg litre^-1N-substituted phthalimide in the pre-priming soak and/or in the PEG further enhanced the results of priming. Leachate removal combined with phthalimide inclusion gave 79% and 86% germination from seeds of two carrot cultivars during the first day in 20°C water following priming. In contrast, cumulative germination of untreated seeds of the same cultivars was 18% and 61% respectively after 3 days in 20°C water. Seeds primed in PEG containing 200 mg phthalimide litre^-1with the solution replaced after the first 24 h germinated earlier and more synchronously than untreated seeds over a range of germination temperatures (5, 10, 15, or 20°C), but the effects of priming were most marked at 5°C.     

Establishing the large scale osmotic priming of onion seeds by using enriched air

Onion seeds were primed in polyethylene glycol solutions (PEG) (-1.5 MPa) for 14 days at 15°C on filter paper and in bubble columns containing 50 g seed litre^-1 PEG using air or enriched air (75% O₂/25% N₂) to aerate and suspend the seeds. Compared with untreated seeds, priming seeds in bubble columns using enriched air increased the percentage seed germination but it did not when air was used, or when seeds were primed on filter paper. Mean germination times (t_m) were significantly reduced in all cases but the reduction was greatest using enriched air and least using air. The spread of germination times was significantly reduced only for seeds primed in enriched air. Drying seeds following priming reduced the percentage germination compared with untreated seeds, but only significantly for those primed in bubble columns using air. Drying also increased the mean germination times by 1.5 to 1.8 days (relative to primed seed which had not been dried). Seeds primed in enriched air were least affected. This increased time is that typically required for water re-imbibition after drying. Priming with enriched air followed by drying gave the same number of normal seedlings as untreated seeds.     

The effects of grading and 'priming' seeds of crisp lettuce cv. Saladin, on germination at high temperature, seed 'vigour' and crop uniformity

Three seedlots of crisp lettuce cv. Saladin were ‘primed’ in 1% tri-potassium orthophosphate (K₃PO₄) or in water for 6 to 12 h and then dried at room temperature. Two of the seedlots were separated into fractions of different mean weight before ‘priming’. The effects of ‘priming’ and grading on crop uniformity, germination at 35°C and root length in a slant test were evaluated. In general, ‘priming’ increased root length in a slant test but there were no consistent beneficial effects of ‘priming’ on seedling size, head weight or uniformity of head weight. Larger seed produced longer roots in a slant test than small seed and gave larger seedlings but seed size had no effect on head weight or cv. of head weight. ‘Priming’ had no effect on germination at 20°C but significantly increased germination at 35°C. ‘Priming’ in K₃PO₄ was more effective than in water. It is suggested that the response of seeds to ‘priming’ varies with seedlot and individual seed weight.     

Effect of osmotic priming, rinsing and storage on the germination and emergence of carrot seed

Carrot seed, osmotically primed in polyethylene glycol solution (273 g/kg water) for 10 days at 15°C, was given 0–5 rinsing cycles, where each cycle comprised agitating the seed in 10 times its own bulk volume of distilled water for 20 to 30 s. Priming decreased the germination and emergence times whether the seeds were rinsed or not, and these effects were maintained even after storage for 450 days. The number of rinsing cycles had no effects, except that seed given five rinsing cycles deteriorated after 270 days storage.     

Responses of Vegetable Seeds to Controlled Hydration

Leek, onion and carrot seeds were imbibed in water and in solutionsof polyethylene glycol (PEG) 6000 over the range –0.5to –4.0 MPa osmotic potential, for periods up to 28 dat 15 C. Seeds started to germinate after 7 and 14 d at –0.5MPa and –1.0 MPa PEG, respectively, but in the lattercase, germination did not exceed 5%. No germination occurredin solutions of lower (more negative) osmotic potential. Seedmoisture content increased with osmotic potential in all threespecies and the relationships were unaffected by the durationof imbibition in solutions of –1.0 to –4.0 MPa,though leek seeds had higher moisture contents than the otherspecies for any given osmotic potential. Linear relationships between response to priming (differencebetween mean germination times of primed and untreated seeds)and seed moisture content were obtained for each species, positiveresponses being obtained above 30–35% seed moisture contentwith optima at 46, 44.5 and 44% seed moisture contents in leek,onion and carrot, respectively. Priming had no effect on embryovolume or cell number per embryo in leek and onion. Carrot embryovolume increased by 43% and cell number per embryo doubled inprimed compared with untreated seeds, whereas seeds imbibedin water showed only a slight increase in cell number per embryoat the stage when radicles were beginning to penetrate the seedcoat. Allium cepa L. cv. Rijnsburger Robusta, onion, Allium porrum L. cv. Winterreuzen, leek, Daucus carota L. cv. Nantaise, carrot, germination, priming, polyethylene glycol, seed moisture, cell number, embryo volume     

The Effects of Priming and 'Natural' Differences in Quality amongst Onion Seed Lots on the Response of the Rate of Germination to Temperature and the Identification of the Characteristics under Genotypic Control

Ellis, R. H. and Butcher, P. D. 1988. The effects of primingand ‘natural’ differences in quality amongst onionseed lots on the response of the rate of germination to temperatureand the identification of the characteristics under genotypiccontrol —J. exp. Bot. 39: 935–950. A screening procedure was applied to define the response ofthe rate of seed germination to sub-and supra-optimal temperaturesfor different lots or sub-lots of two onion (Allium cepa L.)cultivars.Three sub-lots of the cultivar White Lisbon were derived froma control lot by osmotic priming (–1.4 MPa, 20 °C.7 d) alone, by priming and drying and by priming, drying andsubsequently storing the seeds for 7 weeks at 2–5 °C.The major effect of priming was to reduce the thermal time forgermination at both sub- and supra-optimal temperatures. Primingalone also altered the distribution of thermal times at sub-optimaltemperatures. A new equation is presented to describe this variation.In contrast, priming had no consistent effect on base temperature(T_b and little effect on the distribution of ceiling temperatures[T_e(G)]. For the control lot of White Lisbon T_b was 4°C,whilst the best common estimate of T_b for all four sub-lotswas 3.5°C. The mean estimate of T_c(50) for the control,primed and primed and dried sub-lots was 35.5°C.Comparisonof three lots of the cultivar Senshyu Semi Globe Yellow of widely-differingviability showed substantial differences in the thermal timefor germination at sub-optimal temperatures, but no significantdifferences in T_b (P>0.10), the common estimate being 4°C.There was a significant negative correlation between probitpercentage viability and the logarithm of the thermal time for50% germination at sub-optimal temperatures amongst the threelots (P<0.05). The work suggests that base temperature forgermination is a genotypic characteristic which is unaffectedby differences in seed quality. It also shows that the effectof priming, quantified as a reduction in thermal time requirementsfor germination, varies amongst the seeds within a lot. Key words: -Onion, seed germination rate, temperature, priming     

Performance of carrot and onion seed primed with beneficial microorganisms in glasshouse and field trials

Beneficial microorganisms (Clonostachys rosea IK726, Pseudomonas chlororaphis MA342, Pseudomonas fluorescens CHA0, Trichoderma harzianum T22 and Trichoderma viride S17a) were successfully applied to carrot and onion seed during a commercial drum priming process. Applied microorganisms were recovered above the target of at least 1 × 10⁵ cfu g⁻¹ seed following subsequent application of pesticides to the seed according to standard commercial practices of film-coating carrot and pelletting onion seed. Two glasshouse experiments consistently showed that priming improved emergence of carrot seed and that C. rosea IK726 further improved emergence time. Priming improved emergence of onion seed in one glasshouse experiment, but had an unexpected negative effect on emergence in the second experiment, possibly due to the proliferation of an unidentified indigenous microorganism during priming, becoming deleterious in high numbers. In this experiment, the application of beneficial microorganisms during priming negated this effect and significantly improved emergence. For each crop, a series of field trials was also carried out over three years, at two different sites each year. Although some positive effects of different seed treatments were seen on emergence or yield in individual field trials, no consistent effects were found for primed or microorganism-treated seed across all sites and years. However, a combined analysis of data for all years and sites indicated that pesticide application did consistently improve emergence and yield for both carrot and onion. This is the first comprehensive study assessing glasshouse and field performance of carrot and onion seed primed with beneficial microorganisms during a commercial process of drum priming in the UK.     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.): VI. INFLUENCE OF PRIMING ON GERMINATION RESPONSES TO TEMPERATURE AND WATER POTENTIAL DURING SEED DEVELOPMENT

Seed priming (imbibition in water or osmotic solutions followedby redrying) generally accelerates germination rates upon subsequentre-imbibition, but the response to priming treatments can varyboth within and among seed lots. Seed maturity could influenceresponsiveness to priming, perhaps explaining variable primingeffects among developmentally heterogeneous seed lots. In thecurrent study, muskmelon (Cucumis melo L.) seeds at two stagesof development, maturing (40 d after anthesis (DAA)) and fullymature (60 DAA), were primed in 0?3 M KNO₃ for 48 h at 30 ?C,dried, and imbibed in polyethylene glycol 8000 solutions of0 to –1?2 MPa at 15, 20, 25, and 30 ?C. Germination sensitivitiesto temperature and water potential () were quantified as indicatorsof the influence of seed maturity and priming on seed vigour.Germination percentages of 40 and 60 DAA control seeds weresimilar in water at 30 ?C, but the mean germination rate (inverseof time to germination) of 40 DAA seeds was 50% less than thatof 60 DAA seeds. Germination percentages and rates of both 40and 60 DAA seeds decreased at temperatures below 25 ?C. Reductionsin also delayed and inhibited germination, with the 40 DAAseeds being more sensitive to low than the 60 DAA seeds. Primingsignificantly improved the performance of 40 DAA seeds at lowtemperatures and reduced , but had less effect on 60 DAA seeds.Priming lowered both the minimum temperature (T_b) and the minimum (_b) at which germination occurred. Overall, priming of 40 DAAseeds improved their germination performance under stress conditionsto equal or exceed that of control 60 DAA seeds, while 60 DAAseeds exhibited only modest improvements due to priming. Asthe osmotic environment inside mature fruits approximates thatof a priming solution, muskmelon seeds may be ‘primed’in situ during the late stage of development after maximum dryweight accumulation. Key words: Cucumis melo L., seed priming, germination, vigour, development, temperature     

Prediction of the coefficient of variation of carrot embryo length from a germination test

The value of the International Seed Testing Association (ISTA) germination test in estimating levels of variation in embryo length between carrot seed lots was examined. For the two groups of seed lots used, the coefficient of variation (c.v.) of embryo length ranged from 16 to 50%. The c.v. of embryo length was negatively correlated with the numbers of normal seedlings counted after 7 days of germination at 20°C, r_s= - 0·72 D.F. 12 and - 0·82, D.F. 15 for the two groups of seed lots used. Provided the relationship between these two characters is established for each laboratory, it is likely to be useful in identifying seed lots of potentially low c.v. of embryo length.     

Effects of matriconditioning on onion seed germination, seedling emergence and associated physical and metabolic events

The effect of matriconditioning, the physiological presowing seed technique, using Micro-Cel E on Allium cepa L. cv. Czerniakowska seed quality was studied. Several ratios of seeds, carrier, water and time of priming were tested. The most effective treatment for improving onion seed germination at most tested temperatures was priming to a ratio of 2 g seed:1 g Micro-Cel:3 g water for 5 days in light at 15 °C. Matriconditioning greatly improved the germination and emergence percentage, seedling fresh and dry weight and reduced electrolyte leakage compared to that of untreated seeds; this beneficial effect was especially evident at suboptimal temperatures. Matriconditioning improved the germinability of aged seeds, the effect being more pronounced in the more aged seeds. No significant differences in ethylene production by primed and non-primed seeds were observed in the absence of its precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), but its presence during imbibition caused an increase in ethylene production; an enhanced activity of in vivo ACC oxidase in Allium cepa matriconditioned seeds in comparison to untreated seeds, indicates that the endogenous level of ACC is a limiting factor of ethylene production. Likewise, the activity of ACC oxidase isolated from matriconditioned seeds was higher than that from untreated seeds. Higher endo--mannanase and total dehydrogenase activities were observed in primed air-dried seeds in comparing to non-primed seeds.     

Modeling seed germination of unprimed and primed seeds of sweet sorghum under PEG-induced water stress through the hydrotime analysis

The effects of reduced water potential (ψ) on seed germination at 25 and 15 °C in unprimed (UP) and primed (P) seeds of two cultivars of sweet sorghum (cv. Keller and cv. Makueni local), were analyzed through the hydrotime model. Six ψ (from 0 to ?1.0 MPa) in polyethylene glycol 6000 (PEG) solutions were used for the tests. Seeds were primed in 250 g/L PEG solution at 15 °C for 48 h. Decreasing ψ of imbibition solution reduced and delayed germination. At 15 °C seeds germinated less and slower than at 25 °C at any ψ. Seeds of cv. Makueni local exhibited a greater sensitivity to water stress in terms of germination percentage, than seeds of cv. Keller, but they were faster in germination. Osmopriming was beneficial for seed germination, both in terms of final percentage and rate, at any temperature and ψ. The hydrotime analysis revealed that predicted θ _H constant was increased when temperature was reduced to 15 °C and at this temperature median base water potential [ψ _b(50)] for germination was higher (less negative) than at 25 °C. Seed priming shifted ψ _b(50) towards more negative values and reduced θ _H requirements for germination. At 25 °C the two cultivars behaved similarly while at 15 °C cv. Keller exhibited a ψ _b more negative but required a greater θ _H to germinate, indicating a greater water-stress tolerance but a slower germination, than cv. Makueni local. The application of the model allows to identify water stress tolerant cultivars during germination, to include into breeding programs for the selection of well-performing cultivars under stress conditions.     

Viability of onion (Allium cega) seed as influenced by temperature during seed growth

The yield and performance of seeds from crops of winter-hardy, bolting-resistant onion grown at temperatures of 15–16, 18–19 and 22–23°C in 1979, 1980 and 1982 were compared. Yields of seed from crops grown at 22–23°C were lower than those from crops grown at lower temperatures but the seeds ripened between 11 and 32 days earlier. Seeds from crops grown at mean temperatures of above 18°C gave higher percentage germination when imbibed at 30°C than 20°C and they also gave higher percentage seedling emergence than those from crops grown at lower temperatures. Seedlings from seeds produced at mean temperatures above 18°C were heavier than those from seeds of a similar weight but produced at lower temperatures. None of these differences were associated with differences in seed weight, embryo weight or seed dormancy but were positively correlated with differences in seed N-concentration. The differences were also associated with the rate of imbibition of water as high germination, high N-content seeds had a slower rate of imbibition than low germination, low N-content seeds of the same weight.     

Evidence for Repair Processes in Onion Seeds during Storage at High Seed Moisture Contents

Survival curves of four seed lots of onion held at 15%, 20%and 25% seed moisture content (me) and 45 ° C for 24 h showeda fall in seed germination at all moisture contents. The rateof loss of viability was less for seeds held at 20% and 25%me than that of seeds held at 15% me, with low vigour seedsshowing the greatest reduction in the rate of deteriorationat the high moisture contents. This is interpreted as evidencefor the activation of repair processes in seeds during periodsof partial seed hydration and discussed in relation to seedinvigoration treatments. Key words: Seed moisture content; Storage, Repair, Priming, Invigoration     

The effects of osmotic pre-sowing treatment on laboratory germination in a range of wild flower species

Sown seed of many wild flower species have slow or delayed germination which can allow unsown and undesirable species to colonise a prepared site. Ideally all seed sown should germinate immediately. Priming seed in an inert osmoticum can improve synchronisation and speed of germination. The objective of this study was to assess the efficacy of priming on a selection of 60 wild flower species from a total of 21 different families. The majority of the species selected were common constituents of commercial seed mixtures. Seeds were primed in the light at 15^CC for 14 days in a polyethylene glycol ‘6000’ solution giving an osmotic potential of either -10 or -15 bars. Priming had a highly significant effect on speed of germination reducing the median germination time by 2.8 ± 0.27 days in the -10 bar treatment and 1.6 ± 0.27 days in the -15 bar treatment. At the species level, 28 species had significantly reduced median germination times following priming. Priming significantly enhanced the final germination percentage in 15 species and significantly reduced it in eight species, with the adverse effect being more pronounced at -15 bars than at -10 bars. Non-hierarchical cluster analysis showed no clear patterns in response to priming either in relation to the comparative ecology or the plant family of the species tested, with the possible exception of the Leguminosae species. Only one out of six members of this family showed any enhancement in germination rate or percentage. The study demonstrates that a priming treatment could improve speed of germination, in a wide range of commonly sown semi-natural grassland species.     

Catalase is a key enzyme in seed recovery from ageing during priming

Ageing induces seed deterioration expressed as the loss of seed vigour and/or viability. Priming treatment, which consists in soaking of seeds in a solution of low water potential, has been shown to reinvigorate aged seeds. We investigate the importance of catalase in oxidation protection during accelerated ageing and repair during subsequent priming treatment of sunflower (Helianthus annuus L.) seeds. Seeds equilibrated to 0.29 g H₂O g⁻¹ dry matter (DM) were aged at 35 °C for different durations and then primed by incubation for 7 days at 15 °C in a solution of polyethylene glycol 8000 at −2 MPa. Accelerated ageing affected seed germination and priming treatment reversed partially the ageing effect. The inhibition of catalase by the addition of aminotriazol during priming treatment reduced seed repair indicating that catalase plays a key role in protection and repair systems during ageing. Ageing was associated with H₂O₂ accumulation as showed by biochemical quantification and CeCl₃ staining. Catalase was reduced at the level of gene expression, protein content and affinity. Interestingly, priming induced catalase synthesis by activating expression and translation of the enzyme. Immunocytolocalization of catalase showed that the enzyme co-localized with H₂O₂ in the cytosol. These results clearly indicate that priming induce the synthesis of catalase which is involved in seed recovery during priming.     

Hydrothermal time analysis of tomato seed germination responses to priming treatments

Controlled hydration of seeds followed by drying (seed priming) is used to break dormancy, speed germination, and improve uniformity of radicle emergence. To date, empirical trials are used to predict optimal priming conditions for a given seed lot. Since priming is based upon seed water relations, it was hypothesized that the sensitivity of germination to reduced water potential before priming might be mechanistically related to, and therefore predictive of, priming responsiveness. Analyses of germination of 13 tomato (Lycopersicon esculentum Mill.) seed lots at two temperatures (15C and 20C) and three water potentials (0, -0.28 and -0.43 MPa) showed that seed lot germination responses could be quantitatively characterized by parameters derived from thermal time, hydrotime, and hydrothermal time models (R²0.73-0.99). Six of the seed lots were primed at two temperatures (15°C and 20°C) and three water potentials (-1.0, -1.5 and -2.0 MPa) for various durations, dried, and their subsequent germination rates analysed according to hydropriming time and hydrothermal priming time models. The responses of germination rates to priming were characterized by hydropriming time (HP) and hydrothermal priming time (HTP) constants and the minimum water potential (min) and temperature (Tmin) for achieving a priming effect. The values of min and Tmin varied relatively little among tomato seed lots, and the generalized values of min=2.39 MPa and Tmin=9.10°C accounted for 74% (15°C), 57% (20°C), and 62% (across both temperatures) of the increase in germination rates following priming. Nonetheless, while the hydrothermal time models described germination patterns both before and after priming, there was relatively little predictive relationship between them.