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I; . .. . . . . . 5 lint: .13‘ , .3 [kl ..‘:.....O. .,.y ,\A . .. ; .11- I‘..\ r. 1}: L. r. ‘ IIIIIIIIIIIIIII II II IIIIIIII I yams 23 01091 5472 Michigan State University This is to certify that the dissertation entitled Low temperature priming and pregermination of Celery seeds and onion seeds presented by Sheldon Chris Furutani has been accepted towards fulfillment of the requirements for Ph.D. , Horticulture degree m Kym/fl Major pr essor Datew 9?— MS U is an Affirmative Action/Equal Opportunity Institution 0—12771 MSU LIBRARIES m RETURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES will be charged if book is returned after the date stamped below. u Litfiésa LON TEMPERATURE PRIMING AND PREGERMINATION OF CELERY AND ONION SEEDS By Sheldon Chris Furutani A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY T982 ABSTRACT LON TEMPERATURE PRIMING AND PREGERMINATION OF CELERY AND ONION SEEDS By Sheldon Chris Furutani Two systems were developed to pregerminate celery and onion seeds: (1) celery seeds were germinated at lO°C in H20; (2) onion seeds were primed for 8 days in -l.l MPa mannitol solution at 10°C and germinated for 2 days in H20 at l0°C. Both systems produced pregerminated seeds with short enough radicles to prevent radicle injury when sowing with a fluid drill. Seem; Low Temperature Pregermination of Celery Seeds for Fluid Drilling Celery seeds (Apium graveolens L. var. dulce (Miller) Pers. cvs. Florimart l9 and Florida 683) pregerminated at lO°C for T4 days produced 0 to 2 mm radicles. Pregermination at 24°C for 9 days resulted in 0 to 7 mm radicles for 'Florimart l9' and 0 to l0 mm for 'Florida 683.‘ Germination at the lower temperature resulted in shorter, more uniform radicles, but time to 50% germination increased from 6-to l3 days. Total germination was not reduced for either cultivar at either temperature. Sheldon Chris Furutani At lO°C, light and seed leachate removal during priming increased germination 30% over seeds germinated in dark with leachates. Seeds primed for 2 days in -l.l MPa NaCl or C6Hl406 respired over twice as fast as raw seeds. Seeds primed for 6 days did not enhance respiration over 2-day-primed seeds. There were no differ- ences in respiration of seeds primed in NaCl or C6Hl406 solutions. Quantitative analysis of carbohydrates, alpha-amino acids, lipids, and reducing sugars were similar between primed and raw seeds during 8 days of priming and l0 days of germination. To my wife Claire ii ACKNOWLEDGMENTS To my friend and advisor, Bernie Zandstra goes my ”aloha” for his support throughout every step of my graduate study. His guidance has given me a deep appreciation for horticulture. I'll always remember those trips to Sodus and coffee st0ps at Battle Creek that we shared. My sincere thanks to Hugh Price for his patience, support, and friendship. He always made the time to lend me an ear and enlighten me in research. Special thanks to Drs. Robert Herner, Darryl Narncke, and Gene Safir for their support and encouragement throughout my pro- gram. Mahalo nui loa to my fellow graduate students for their friendship. Life as a student would not have been the same without them. TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES INTRODUCTION Chapter I. REVIEW OF LITERATURE Factors Affecting Germination Water . . . . . Temperature . Light . . . Improved Speed and Uniformity of Germination Soaking . Hardening Priming . Pregermination II. PREGERMINATION AND INCUBATION OF CELERY SEEDS . Introduction Materials and Methods Pregermination . Incubation Transplants . Results . . Pregermination . Incubation Transplants . . Discussion and Conclusion . Effect of Light, Seed Leachate, and Temperature on . Germination Effects of Temperature on Pregermination Incubation . . . . . . . III. PRIMING AND PREGERMINATION OF ONION SEEDS Introduction iv Page vi vii Q) NCDNUWU'l-b-bww Chapter Materials and Methods Priming Physiological Effects of Priming on Onion Seeds . Pregermination . . . . . . . . . Results . Priming Physiological Effects of Priming Onion Seeds . Pregermination . . . Discussion and Summary . Priming Onion Seeds Leakage Studies . Food Reserve Utilization Studies . Respiration Studies Pregermination Studies BIBLIOGRAPHY Table LIST OF TABLES Height, number of leaves, and weight of 28-day—old celery plants grown in the greenhouse from raw and pregerminated seeds . . . . . Priming solutions used in these experiments . Germination of onion seeds at l0°C after priming for 24 and 48 hr in various solute solutions . Germination of onion seeds at l0°C after priming with mannitol solutions . . . . . . . . . Main effects of solute and priming duration on onion seed germination . . . . . . Emergence of seedlings from raw, primed, and primed— pregerminated onion seeds . . . . . vi Page 39 48 62 63 65 103 Figure 10. 11. 12. LIST OF FIGURES Germination of 'Florimart 19' after 8 days at 24°C Germination of 'Florimart 19' after 20 days at 10°C Germination of 'Florimart 19' and 'Florida 683' at 10 and 24°C in aerated columns Percent germination and days to 60% germination of 'Florimart l9‘ and 'Florida 683' celery seeds germina- tion at 10 and 24°C in aerated columns . Pregerminated seeds of 'Florimart l9' and 'Florida 683' after 80% germination at 10 and 24° C in aerated columns . . . . . . . . . . . . Effect of germination temperature on radicle lengths of seeds of 2 celery cultivars pregerminated in aerated columns . . . . . . . Days to 50% emergence of celery seedlings from raw (R) and pregerminated (P) seeds incubated in dark growth chambers at 20°C . . . . . . . . Emergence of WWorimartl9' and 'Florida 683' celery plants from raw (R) and pregerminated (P) seeds sown in flats and placed in dark growth chambers at 20 or 32°C . . . . . . . . . Emergence of 'Florida 683' celery plants from raw and pregerminated seeds sown in flats and placed in a greenhouse with 22°C day and 16°C night temperatures Relationship between days to 50% germination and days of priming at 10°C on onion seeds . . Relationship between days of priming at 10° C and spread of germination . . Leakage of alpha-amino acids, reducing sugars, and 262 mu absorbing substances from raw and primed onion seeds during 5 hr imbibition in water at 10°C vii Page 20 22 24 26 29 31 33 37 66 68 70 Figure Page 13. Water content of raw and primed onion seeds imbibing in water at 10°C . . . . . . . . . . . . . 73 14. Leakage rates of alpha-amino acids, 262 mu absorbing substances, and reducing sugars from onion seeds at 24°C after 2 hydration-dehydration cycles . . . . 75 15. Leachate optical densities of imbibing solution after priming of raw onion seeds at 10 and 24°C with NaCl and H20 . . . . . . . . . . . . . . . . 77 16. Water content of onion seeds after various treat- ments . . . . . . . . . . . . . . . . 79 17. Food reserve levels of onion seeds during priming in -1.1 MPa NaCl solution at 10°C . . . . . . . . 81 18. Food reserve levels of raw (dotted line) and primed (solid line) onion seeds after sowing and incubation at 10°C . . . . . . . . . . . . . . . . 84 19. Oxygen uptake of onion seeds during imbibition in various solutions at 10°C . . . . . . . . . . 86 20. Water content of onion seeds during imbibition in various imbibing solutions at 10°C . . . . . . . 88 21. Oxygen uptake of onion seeds at 10°C after various priming treatments . . . . . . . . . . . . 90 22. Water content of onion seeds at 10°C after various priming treatments . . . . . . . . . . . . 92 23. Oxygen uptake of onion seeds at 10°C after various priming treatments . . . . . . . . . . . . 94 24. Water content of onion seeds at 10°C after various priming treatments . . . . . . . . . . . . 97 25. Three-way interaction of temperature of priming by days primed by germination temperature for radicle length . . . . . . . . . . . . . . . . 99 26. Three-way interaction of temperature of priming x days primed x germination temperature for days to 50% germination . . . . . . . . . . . . . . 101 viii INTRODUCTION Onion and celery are economically important crops that germinate slowly and emerge from the soil nonuniformly. At harvest, these cr0ps are at various stages of maturity, which results in non- uniform onion bulbs and celery stalks. In these crops, bulb and stalk size determines the value of the crop. The conventional method to sow moSt vegetables is direct seeding. In this method, seed germination in the field can be a slow process especially under cold soil conditions. As a result, plant emergence is nonuniform and delayed, producing nonuniform crop maturity. Pregerminating the seeds before planting in the field increases the speed and uniformity of seedling emergence. Crops from pregerminated seeds also mature earlier and more uniformly than raw seeds. Fluid drilling has been successfully used to sow pregerminated seeds in crops such as tomatoes and peppers. This system of sowing suspends pregerminated seeds in a fluid gel carrier and extrudes them into the soil. The advantages of such a system are: (l) faster and more uniform emergence; (2) and more uniform crop size and matur- ity. Fluid drilling, however, is limited to sowing seeds with short, uniform radicles. Since onion and celery seeds germinate nonuniformly, they produce long and short nonuniform radicles. The pregerminated seeds with long radicles are injured during the fluid drilling operation. The objectives of this study were: (1) to develop systems to pregerminate onion and celery seeds with short radicles; (2) to determine the effects of priming onion seeds; (3) and to investigate physiological and biochemical changes which occur during and after priming of onion seeds. CHAPTER I REVIEW OF LITERATURE Factors Affecting Germination The germination of seeds is, in most cases, dependent on external environmental factors such as water, temperature, and light. The level of each factor required for germination varies with seed and species. Ila—te: Availability of water is probably the most important factor in seed germination. Normally, when a nondormant seed comes in con— tact with water, the seed imbibes water and germinates. However, some seeds are unable to imbibe water due to impermeable seed coats. Several methods are used to overcome resistance to water uptake through impermeable seed coats: mechanical abrasion, chemical scarification, and impaction (removal of the strophiolar cleft) (70). The amount of water taken up by seeds is dependent upon internal food reserve composition. Of the food reserves found in seeds, protein has the greatest capacity for water uptake. Starches and fats have a low capacity for water uptake (70). Therefore, seeds that swell upon imbibition contain large quantities of protein. Seeds that do not swell during imbibition are low in protein com- position (70). After water has entered the seed, membranes and other cellu- lar components begin to hydrate and biochemical processes leading to germination are initiated. Within the seed, the embryo elongates and the radicle eventually penetrates the seed coat; this penetra- tion is commonly referred to as seed germination (7). Temperature Seeds of different species have different temperature require- ments for germination. Some seeds, such as celery and lettuce, become dormant above a critical temperature. This condition is called thermodormancy (110). Seeds such as watermelon and okra germinate well above 35°C, but do not germinate at temperatures below 15°C (47, 90). Other seeds, such as onions, germinate well at both high and low temperatures (116), but the speed of germination is much slower at lower temperatures. Nagenvoot et al. (116) described the optimum germination temperature of seeds as a function of heat units. They contended that optimal heat units improve the germination of nonuniform germinating seeds such as onions, carrots, and celery. Liam Seeds of some species germinate better in light than in dark. Pressman et a1. (87) reported that celery seeds incubated in the dark did not germinate at 25°C, whereas those in the light (white light) germinated. The celery seeds in light germinated as light elevated the critical temperature of thermodormancy (110). The response of celery seeds to light is mediated by phyto- chrome (110). Lettuce seeds have a similar phytochrome—mediated response (45, 48, 115). Thus, uniform germination of celery and lettuce seeds is dependent upon optimum light and temperature levels. The light requirement of celery seeds can be replaced, to a degree, by growth regulators and inorganic salts. Combinations of gibberellins and cytokinins have been reported to raise the tempera- ture at which celery seeds become thermodormant (8, ll, 12, 110). Solvents, inorganic salts, and growth regulators have also been shown to overcome the light requirement of seeds of several species (55, 70, 113). Improved Speed and Uniformity of Germination Seed germination is often a slow and erratic process, result- ing in nonuniform crop stands. Poor or slow germination is caused by a number of factors including suboptimal environmental conditions, seed dormancy, and nonuniform maturity of seed embryos. Several techniques can be used to improve germination such as soaking, harden— ing, priming, and pregermination. Soaking Soaking is the process in which seeds are placed in water and allowed to imbibe for a period of time before planting. Tincker (112), Chippendale (16), Taylor (108), and Haight and Grabe (39) reported that soaking seeds in water prior to planting resulted in accelerated germination of several crop species. Chippendale (l6), working with cocksfoot (Dactaylis glomerata L.), speculated that soaking seed increased water uptake through the palea, thereby accelerating germination. Later, Haight and Grabe (39) measured the rate of water uptake of soaked and nonsoaked cocksfoot seeds and found no differences. However, soaked seeds consumed more oxygen during the first 12 hr of imbibition than did nonsoaked seeds. Extended periods of soaking in water may injure seeds of some species. Kidd and West (58) observed that soaking periods of 12 hr or less decreased the time to emergence of pea, dwarf bean, barley, and sunflower seeds without injury (58). However, soaking the seeds for 24 hr inhibited root growth. Increasing the soaking period to 48 hr seriously inhibited root growth and injured the cotyledons. Similar observations have been reported with peas by Larson and Lwang (62) and Perry and Harrison (83). Several methods to reduce injury during extended periods of soaking in water have been reported. Eyster (28) reduced soaking injury in beans and peas by allowing the seeds to imbibe slowly on wet filter paper before soaking in water. Perry and Harrison (83), Powell and Matthews (85, 86), and Woodstock and Tao (119) also reduced soaking injury by partially submerging pea seeds in an osmotic solu- tion prepared with polyethylene glycol 4000. The polyethylene glycol solution created an osmotic tension surrounding the seed, lowering the osmotic gradient between the soaking solution and the interior of the seed. Reducing the osmotic gradient decreased the rate of water uptake and prevented seed injury. Orphanos and Heydecker (80) hypothesized that oxygen defi- ciency in the interior of the seed cavity between the cotyledons is the major cause of soaking injury. During soaking, the seed cavity becomes flooded and excess water is trapped within the cavity. The flooded seed cavity swells, creating high internal pressure, thus lowering gas diffusion into the seed. The seed is injured by ana— erobiosis. In contrast, Barton (4, 5) demonstrated that supplying oxygen during imbibition of pea seeds is more lethal than supplying air. Hardening Hardening refers to the process of imbibing a seed for a given period of time and then redrying it back to a given level of storage moisture. The redried seed is said to be "hardened.“ Seeds may be soaked and redried ("hardening cycles") several times before planting. May et a1. (69) speculated that hardening preconditions seeds to germinate and develop more rapidly under dry conditions. Hafeez and Hudson (38), however, reported faster germination and development of hardened radish seeds under optimal moisture and fertility condi- tions, but no increased growth under dry conditions. Austin et a1. (3) and Currah and Salter (19) found that 3 cycles of hardening were optimal for carrot seed germination in the field. The effect of hardening on carrot seed was further improved by limiting the volume of water taken up during each cycle to 70% of seed weight. Longden (65) reported similar results with sugar beet seeds using 3 hardening cycles. Hardening seeds of forage grasses (1), wheat (66), and pepper (56), has also increased the speed of germination over non- hardened seeds. Hardening allows morphological development of the embryo to proceed without radicle penetration through the seed coat. Austin et a1. (3) demonstrated that the embryo in carrot seeds actually increased in size with each hardening cycle. They observed that after 6 hardening cycles, the size of the embryo doubled and the number of embryonic cells increased 6 times over nonhardened seeds. Hardening does not always increase the speed of germination of seeds. Hegarty (42) reported slower germination of corn seeds when they were soaked for 16 hr and redried. Berrie and Drennan (6) observed radicle and plumule injury in oats and tomatoes after 3 hardening cycles. Taylor (108) found a serious decline in germina- tion of celery seeds after redrying. More recently, work by Biddington et a1. (12) has shown that the rate of redrying imbibed celery seeds can seriously affect percent germination. Nhen imbibed celery seeds are dried too quickly, cell membranes appear to become disrupted. Sen and Osborne (101), and McKersie and Tomes (72) reported damage to newly synthesized ribosomal RNA in embryos of imbibed wheat, wild oats and birdsfoot trefoil upon dehydration of imbibed seed. Priming Priming is the process of soaking seeds in an osmotic solu- tion instead of water in order to decrease the rate of imbibition. Organic and inorganic salt solutions have been used for priming seeds. Kotowski (59) observed a stimulation of germination of pepper seeds after priming for 48 hr in 0.2% and 1.5% salt solutions. Solutions of NaNO3, MgClz, or MnSO4 gave the best results in increas- ing the total germination of pepper seeds. Doyle et a1. (23) obtained increased germination of freshly harvested wheat, oats, barley, and flax by priming the seeds in a dilute KNO3 solution prior to planting. However, priming of 6-month stored seed did not improve germination. Some early work by Hashimoto (41) with photoblastic tobacco seeds showed an enhancement of germination with NH4+ and N03_ solu- tions. The addition of gibberellin to the N03' solution was syner- gistic in promoting tobacco seed germination. Gibberellin replaced the tobacco seeds' requirement for light and the N03- complex pro- moted germination. Later, Roberts (88) elucidated the mechanism of the nitrate-light replacement effect on weed seeds. Currently, the International Seed Testing Association (54) recommends using KNO3 to ”break” dormancy of seeds of many plant species. Sachs (90) revealed that replacing the light requirement of some seeds is not the only beneficial response of priming in salt solutions. He demonstrated a reduction of the heat requirement for germination of watermelon seeds with KNO3 + K3PO4 or KCl osmotic solutions. Levitt and Hamm (63) found increased speed of germination when seeds of Taraxacum kok-sahgyz were primed in an osmotic solution. They further reported that the speed of germination could be altered 10 by regulating the concentration of inorganic salt in the osmotic solution. Ells (25) reported similar results with tomato seeds in osmotic solutions formulated with NaCl or KNO3 + K3PO4. Ells (25) and Levitt and Hamm (63) hypothesized that regu- lating the moisture level within the seed increased the speed of germination. The seeds' moisture level can be kept low with a strong osmotic solution. The low moisture level permits biochemical ger— mination processes to proceed, but prevents radicle protrusion and complete germination of the seed. This hypothesis is supported by Woodstock's work, in which primed tomato seeds consumed more 02 than nonprimed seeds (118). Oyer and Koehler (81) demonstrated with tomato seeds that the advancement of germination produced by priming does not occur in the absence of oxygen. More recently, Coolbear and Grierson (17) and Coolbear et al. (18) measured large accumula- tions of nucleic acids, especially ribosomal RNA in osmotically primed tomato seeds, further supporting E115 and Levitt and Hamm's early hypotheses. Excessive salt concentrations in priming solutions can be detrimental to subsequent seedling growth. Sugar beet seeds primed in 0.4 to 1.0 molar NaCl solutions exhibited severely stunted radicle growth and seedling development (24). High concentrations of ions such as sodium may be toxic to seeds being primed (47). The speed and uniformity of germination has been increased by priming seeds with lower concentrations of NaCl. Ells (25) and Malnassy (67) did not observe any injury or decrease in germination 11 with tomato seeds primed in 1.5 to 2.0% NaCl or KNO3 + K3P04 solu- tions. The tomato seeds primed in either salt solution had greater speed and uniformity of germination than nontreated and hardened tomato seeds. Polyethylene glycol (PEG) has been used extensively for prim- ing seeds at low temperatures. Several reports (43, 45, 49, 50, 51, 52, 120) indicate that there is a more rapid and uniform germination and emergence of seedlings when vegetable and ornamental seeds are primed in a PEG solution. Similarly, Akalehiywot and Bewley (13) found that oats and wheat germinated more rapidly and uniformly when primed at 10°C than at 24°C. Priming at low temperatures extended the period to radicle protrusion, permitting biochemical advancement to proceed beyond priming at higher temperatures. Salter and Darby (95) prevented emergence of celery seed radicles for 21 days by soak- ing in a -10 bar PEG solution at 15°C. They observed that seeds primed at 15°C reached 50% germination in 1.4 days, compared with 13.7 days for nonprimed seeds. Some primed seeds lose most of the benefits of priming when they are redried to their initial moisture content. Heydecker (43) and Gibbins (49), and Heydecker et a1. (50, 51) observed that redrying onion seeds primed with a -10 bar PEG solution for 23 days at 10°C resulted in a 50% reduction in the benefits of priming. The primed and redried onion seeds germinated more slowly than primed and non- redried seeds. Heydecker and Gibbins (49) explained that the time difference between the germination of redried and nonredried primed 12 onion seeds is far greater than the time needed for rehydration. They suggested that degradation of ribosomal RNA and other newly synthesized protein products occurs during redrying, resulting in delayed germination for redried-primed seeds. The PEG solution, as an osmoticum for priming seeds, must not allow the seed to germinate completely, yet provide sufficient water to initiate germination processes. PEG 6000 is a chemically inert molecule which does not enter or react with seed tissue. Unlike PEG, smaller nonelectrolites such as glycerol, sucrose, and mannitol enter and react with seed tissues (68). Other desirable properties of PEG include long-term osmotic stability (111), and a quadratic relationship between concentration and osmotic potential (74). How- ever, the availability of oxygen in PEG solutions is limited. Heydecker et a1. (44) found a decline in total germination of seeds when soaked with increasing concentrations of PEG. Mexal et a1. (73) reported a 50% reduction I1oxygen diffusivity in a -13 bar PEG solu- tion. Attempts to increase oxygen levels in PEG solutions by aera- tion have had little success due to their high viscosity (84, 97). Pregermination Pregermination or ”chitting“ is similar to soaking, but the process is continued until the radicle emerges. The seeds are then planted using a "fluid drilling" system. Pregermination of seeds produced faster and more uniform germination than soaking, hardening, or priming (20, 36, 92, 93, 94). Biddington et a1. (10) demonstrated that fluid-drilled pregermination celery seeds emerged 25 days l3 earlier with greater percent emergence than fluid-drilled nonpre- germinated celery seeds. In similar work, Currah (21, 22), Currah et al. (20), Entwistle (26), Steckel and Gray (105) and Lipe and Skinner (64) increased the speed and uniformity of emergence of onion seeds with pregermination. Research on fluid drilling of pregerminated seeds with long radicles has shown varying results (36). Radicles longer than 5 mm may be mechanically injured during the fluid drilling operation (95). Damage to the radicles reduces the speed, uniformity, and total emergence of the crop. Maintenance of radicle lengths of l to 2 mm has reduced injury of fluid-drilled pregerminated lettuce seeds (34, 35). More uniform emergence has resulted from fluid drilling tomato seeds having 1 to 2 mm radicles than with longer or shorter radicles (14). In some crops, such as carrot, onion, celery, and leek, mor- phological development of the seeds is irregular. Nonuniform embryo maturity results from irregular morphological development. There- fore, these seeds germinate sporadically with large variability in radicle lengths (47). Salter and Darby (95) have shown that priming celery seeds in a -10 bar PEG or -10 bar KNO3 + K3PO4 solution at 15°C for 21 days reduced the variability in radicle length of celery. The improvement in uniformity of radicle length was attributed to the greatly increased uniformity of germination attained by priming the celery seed. CHAPTER II PREGERMINATION AND INCUBATION OF CELERY SEEDS Introduction Germination of celery seeds in the field is slow and sporadic resulting in delayed and nonuniform stand establishment, especially under cold soil conditions (10). Therefore, most celery crops are started in greenhouses and transplanted outdoors. Greenhouses pro— vide more favorable germinating conditions for celery seeds than direct seeding in the field. However, even under greenhouse condi~ tions, celery seed germination can be nonuniform. Attempts to improve the germination of celery seeds with growth regulators have been only partially successful in overcoming the phytochrome- mediated dormancy in celery seeds (9,11,109). An alternative method to improve the uniformity and speed of emergence of celery seeds is to pregerminate them prior to planting. The pregerminated seeds are then sown by suspending the seeds in a fluid gel and extruding them into the soil with a fluid drill. Currah et a1. (20) and Biddington et a1. (10) established earlier and more uniform celery stands with fluid drilling using partially pregerminated (mixture of imbibed and pregerminated) seeds than with nonpregerminated (raw) seeds. Radicles of pregerminated seeds must be short and of uniform length in order for fluid drilling to provide the greatest improvement 14 15 in rapid and uniform emergence. However, uniform radicle length is difficult to attain due to the nonsynchronous nature of celery seed germination (36, 47). Nonsynchronous germination results from irregular embryo maturity due to time differences in initiation of umbels, pollination of florets, and embryo development (47). Further- more, attempts to fluid drill pregerminated celery seeds with radi- cles longer than 5 mm have resulted in radicle injury (95). Celery seed germination is more uniform when seeds are primed with poly- ethylene glycol or inorganic salts (95, 96). The objectives of this study were: (1) to determine the effect of low temperature germination on celery seeds; (2) to com- pare the emergence of pregerminated and raw celery seeds under Opti- mal (20°C) and high (32°C) temperatures; and (3) to compare the uni- formity of plants gorwn from pregerminated and raw celery seeds. Materials and Methods Pregermination The Effect of Seed Leachate, Light, and Temperature on Germination Celery (Apium graveolens L. var. dulce (Miller) Pers. cv. Florimart 19)1 seeds were germinated in glass columns containing 2 9 seed and 400 ml distilled water. The water in the columns was aerated continuously, with an air stone placed in the bottom of each column. 1Celery seeds were obtained from the Keystone Seed Co., Inc., Hollister, California. 'Florida 683' Lot no. 19-031-005 dated November 1978. 'Florimart 19' Lot no. 19-027-005 dated November 1980. 16 To determine the effects of seed leachate, light, and tem- perature, the seeds were germinated, as described above, under light or dark with 3 intervals of leachate removal at 10 or 24°C. The leachates were removed at either 24 or 48 hr intervals or not at all, to remove potential germination inhibitors (96, 108). Leachates were removed by decanting-off the water in the columns and replacing it with distilled water. For the light requirement, columns were illuminated with 2 G.E. 40 watt cool, white fluorescent lights, 1.2 m in length, placed 2 m transverse to the sides of the columns. For the dark treatment, columns were wrapped with a single layer of aluminum foil to prevent light penetration. Germination counts were taken daily on an aliquot taken from each column. A green safe light was used for viewing germination in the dark treatment. Each treatment was replicated 3 times (3 columns) in a completely randomized design. The Effect of Temperature on Pregermination Seeds of 2 celery cultivars, 'Florida 683' and 'Florimart 19' were germinated in aerated columns as described above, with 24 hr leachate removal, at 10 and 24°C. The seeds were illuminated during the entire experiment. Radicle lengths were measured at approximately 80% germination by sampling 100 seeds of each cultivar at 10 or 24°C. Six by nine inch photographic prints from slides (1:1 enlargement) of the ger- minated seeds were used to measure the radicle lengths. Germination counts were recorded daily using a dissecting microscope at 7 X. 17 The treatment combinations were 2 cultivars x 2 germinating tempera— tures. Each treatment was replicated 4 times (4 columns). Incubation The Effect of Temperature on the Emergence of Raw and Pregermi- nated Seeds 'Florida 683' celery seeds were pregerminated at 10°C in light for 14 days, as described above. After reaching 80% germina- tion, they were sown 2 mm deep in flats containing moistened No. 2 grade vermiculite. Raw celery seed was planted as a control. The flats were placed in temperature-controlled growth chambers in the dark at 20 or 32°C. The flats were watered by subirrigation. Seed— ling emergence was recorded daily. Each treatment was replicated 4 times using 30 seeds per replicate. The treatments were arranged in a completely randomized design. Transplants A Comparison of Transplants Grown from Raw and Pregerminated Seeds Seeds of 'Florida 683' were pregerminated at 10°C, as described above. Pregerminated and raw seeds were sown 2 mm deep in flats (Speedling trays No. 100 A) containing peat and vermiculite (1:1). Each treatment was replicated 8 times using 20 seeds per replicate. The celery seeds were grown in a greenhouse with 22°C day and 16°C night temperatures. Seedling emergence was recorded daily. 18 Plant measurements were taken 28 days after sowing, to deter- mine the growth differences between plants grown from pregerminated and raw seeds. Number of leaves, plant heights, and shoot dry weights were recorded. Coefficient of variability (CV) within treatments was used to compare plant uniformity (106). The coeffi- cient of variability was calculated using the following formula: CV met x CV = coefficient of variability EMS = error mean square 2 = treatment mean Days to 50% emergence and percent emergence were also calculated for the treatments (79). The formula used to calculate days to 50% emergence is as follows: 0 = Z fx/Zf D = days to 50% emergence f = number of seeds germinated on day x x = days after sowing Spread of germination (T90 - 110) was calculated by probit analysis (109). Duncan's multiple range test was used in mean separations. 19 Results Pregermination Effect of Light, Seed Leachate, and Temgerature on Germination Over 80% of the celery seeds germinated in light at 24°C when seed leachates were removed. Without leachates removed, about 25% of the seeds germinated in light (Figure 1). Seeds incubated for 8 days at 24°C in the dark did not germinate, regardless of whether or not the leachate was removed. At 10°C, more than 90% of the seeds germinated in light with leachates removed, while only 72% germinated without leachates removed (Figure 2). More than 60% of the seeds germinated in the dark, regardless of the presence of leachates. Effect of Temperature on Pregermination Temperature affected the time to total germination (Figure 3). At 24°C, seeds of 'Florida 683' attained total germination in 7 days, while 'Florimart l9' reached total germination in 8 days. At 10°C both cultivars required 15 days for total germination. Total germi- nation at 10°C took 6 to 9 days longer than at 24°C. Temperature did not affect total percent germination of seeds of either culti- var (Figure 4). Temperature did not affect days to 50% germination (Figure 4). The time required to reach 50% germination at 10°C was approximately twice that required at 24°C. There was no difference in cultivar response to germination temperature. 20 .mcowpwv>wv vcmucmpm pcmmmcamc mean co mmCTF _mowpcw> .mzen m com Amzv uw>oEwL go: go .L; we .;c «N xcw>w Uw>oEmL mm: mpmgomw— vwmm .Uovm pm mzmw w empIm _m_ “cmevcord. +0 COIpmcwEwa .F wizard 21 FIG...— _I_ #10... _+_ :2 2. we 2% . mz £2. ZO_.—.mu ucmvcwpm pcmmmcaoc mosa~ Fmowpcw> .mxmv w Low Amzv Uw>oEmc go: no .c; we .c: «N >cm>m uw>oewc mm: wumcomm_ comm .ooo— pa mzmu om LmIIm .m— “Legato—u. Io cowpwszme .N magma; GERMINATION AT 10°C 23 1111111 oRSSSBS NOILVNIWHES lNEOHEd I o F l 0 NR 24 hr 48hr NR [-1 LIGHT 48hr 24hr [+1 LIGHT 24 .mcE:_oo uaamtae e? Seem use o_ pa .mwe wetto_a_ new _m_ pee5220_a_ to eowpmcchmw .m mczmwd 25 zzsqoo oupcmmc zH m>¢o .3 53.59:. .m. .30 3.3.3.. .0. uo¢u om AUDINOIIUNINUEO lNBOUEd Figure 4. 26 Percent germination and days to 50% germination of ‘Florimart l9' and 'Florida 683' celery seeds germi- nated at 10 and 24°C in aerated columns. Mean separa- tion by Duncan's multiple range test, at 5% level. 27 10°C 24C 'FLORIDA 683' .L%E__ // q . q . _ . . q . O 0 0 O o 0 5 0 5 0 8 6 4 2 2 ‘l .I 10 C 24 C 'FLORIMART 19' 100 ZO_._.m_ am pm mummy mace; w_g_p_:e m_:moczo x2 Cowpecmawm cmwz .oon to em we mengmso cpzocm xcmu c? umomFQ use mpg—w c? czom mummm Aav umumcwacmmmca use Amy 3e; Eoc+ mpcmra Ace—mo .mmo meaco_d. u:m_m_ pcmevno_d_ Io wocmewEm .m wczmmd . ~ |I||||||||llllllllIIllllllIllllllllllllllllllllllllllllllllllllllll Q 0 V N BONESUEWE .LNEGHEd FLOR IDA 683 FLORI MART 19 37 ._m>w_ xm pm .omu an mezzpoo :wzpwz wove; Imamm mew: mcmmz .coFHMCFEme Io newcam u um .copua:PEme &om on warp" omp .mmczpmcmaawa “so”: coop use Ame momm cuPz wmzo;cwmgm m c, cmomPQ ucm mac—w :P czom mummm umpmcpscmmmca new 3m; Eocm mp:m_a xcmeo .mwo vaLOFd. Io mocwmcmEm .m mesmwd 38 up 2 wszow MERE w>¢o n— C o A m rs ,WM ur- P d a a... 3mm awn cognizant... om one limzal >>w3cw wwom uwpcmammlr.u u << mpcmFm>wzcw mmoo:_mlc u om xpamcmc quwugo mpmcome u com mo.oams coc sax .mopmuw_amc a +0 mamas mew mw=Fm> .uoo_ pm Lopez cw :owpwnwnsv c; m mcwczv mvmwm cowco umewca vcm 38c Eocm mmucmpm unam mcwncOmnm 15 wow use ,mcmmzm mcwozcwc .muwom ocwEmlm:a_m mo mmmxmmb .N_ acsmaa 71 V 111.11 393 ALISNHO 'IVOILdO SLVHOVB'I O O O O at a 5' o‘ i} 13 < . 4 <1: r 1 a. a ,, _.,, (D b o - o: (D ‘h D: 8 355’ g E 8 F—' co 3: .l :I c: a, .- .I' . ..O ..:O. .‘o ....q.q .. 4 ”N I.. . ..... d"... l 4. ~— 8 a a a a .1» a m e .1. 0° m 01 o k m N c N in 01 N N N II- I— u— ,- 0 (1» up Bun/611) smawmnoa asoome—p 27- 21" 18- IS- 12" 1 1 1 6‘) O V m m N ' (W “P 5/“l/5") SLNB'IVAIROB CIIOV OIlHVdSV-IP 1111 Geno HOURS of IMBIBITION 72 Effect of hydration and dehydration on leakage of alpha- amino acids, 262 mp absorbing substances, and reducing sugars from raw seeds. Alpha-amino acids, reducing sugars and 262 mp absorbing substances leaked more during the first hydration cycle than during the second hydration cycle (Figure 14). Leakage of seeds during the first and second hydration cycles were parallel, although leakage during the second cycle was 50% lower than during the first cycle. Effect of osmotic potential and temperature on leakage of 262 mp absorbing substance. At 24°C, seeds imbibed in H20 exhibited the greatest leakage; at 10°C, seeds imbibed in -l.1 MPa NaCl leaked the least (Figure 15). Seeds primed in H20 at 10 and 24°C and in -l.l MPa NaCl at 24°C contained a comparable level of H20 (Figure 16). However, after 2 hr of imbibition, seeds primed in -1.1 MPa NaCl at 10°C contained less water than seeds primed in the other treatments. Food Reserve Utilization Studies The utilization of food reserves during priming. The quantity of food reserves (reducing sugars, carbohydrates, alpha—amino acids, and lipids) was constant over 8 days of priming in -1.1 MPa NaCl at 10°C (Figure 17). Food reserve utilization during germination. During germina- tion, there were only slight differences in the quantity of food reserves used by primed and raw seeds (Figure 18). Food reserves of primed and raw seeds decreased at a similar rate as germination pro- gressed. 73 ._m>m_ xm pm pmmp d An pcmowwwcmwm we: u m: .000? pm cape: cw meanwoew mcmwm cameo emswca can gm; do #cmpcoo cmpmz .mF wtsmta 74 ZO_._._m_ms: ”.0 wEDOI 4p." 1 1 H m ¢ m N no.5... .m. H 308.. 888 3mm .o. 2953: @552; (5 c: to d1 1‘1M Mp fi/Ju/Bwl memos HELVM 75 mpcmpm>wscm vwom owpmcmamwup .u u << mpcm~m>vzom mmoo:_m-u n ma xpwmcmu _mowpao mpmsommF n 904 mo.ooms 20c sax .—m>m_ &m we am; an cowpmcmawm cam: .mmFoxo :ovumcuxgmvlcowpmcuz; N cmpmm goam pm mvwwm cowco scam memozm mewozumc ccm .moocmwmnzm mcwnc0mne as mom .muwom ocwsmlmcarm Io mmpmc mmmxmmm .32 eczema 76 vrlul 393 ALISNSCI 1VOIld0 BLVHOVB'I 1°. N. °. 0°. *2 V: N. O. T 7 : '2' 9 <9 ‘2 2 O I I <1 0M 2 ’III c u 0 o :2 5 :5 g I .2126 I4 0 "1' 3: .3 °' 9 >. 1; .c .0 f 8 -n ‘0 o .: 0 LI, 0) ~04 <1~° 0 ~— F l I ] o c o o o c: o o o 0 ¢ 6') N '- 0(1M MP 5/14/5“) SLNB'IVAIDOB asoome-p l I I I l l I l l o o c o o o o o o 2 z e. 2 ° 0 s a I (1M MP 6Nil/5'1) smanvmnoa OIOV OILUVdSV-IP HOURS of IMBIBITION 77 .mmpmompawc v we mcwms mam mm:_m> .ow: vcm Fonz saw; poem new ofi we mummm cowco 38L wo mewswca cmpwm cowp:_0m m:_awaew do mmwuwmcwu Fmowpao mumgommb .mp mason; 78 62:25.1 .5 w> .mmumow_amc a we .mpcmEpmmcp mzowcm> cmpmm mummm cowco do pcmpcoo Lopez .8_ mcsm_a 8O ZO_._._m_m—2_ ”.0 mmDOI m e m p N N .002 was. 5... 0°C.. 1*. mod ow... coo—wt. H om; .omz was. 5- oovu 11 N o I OoVN $- 33.53: 9555 .éoo l'lM Mp B/Ju/Bwl mamoo HELVM 81 .Avmv mcowpww>wu ugmvccpm pcmmwgamg mgmm .uoop pm nevus—om Fonz on: _.F- c? mcwswga m5wgzv mvwmm cowco $0 m—w>w— w>gwmwg woo; .N_ wgzmwu 82 ZO_._.D._Om 02.5.35 2. m><0 mH |\\I/ 23.5 9.6300". .rll! umH \/\/ moumbgnoemo FIIF o . u IV '00—. umH «Eon 0589932 ICON [OK In— I: In— 6 fi/Bw 83 Primed seeds lost more seed weight and gained more radicTe dry weight than raw seeds, 5 days after sowing. At 10°C, primed seeds germinated in 3.7 days, whiTe raw seeds took 6.9 days to ger- minate (Tabie 5). This accounted for the differences in seed and radicie weight. Raw seeds had Tost 13% and primed seeds Tost 10% of their weight, 10 days after sowing (Figure 18). The difference in radicTe weight between raw and primed seeds was Tess than 10 mg on the tenth day after sowing. Respiration Studies Effect of soTute on respiration. Respiration rates of seeds imbibed in a1] soiutes were the same untii O to 400 minutes. There- after, H20 imbibed seeds respired significantiy more than seeds imbibed in aTT other soiutes (Figure 19). There were no differences in respiration between NaCT and mannitoT imbibed seeds. There were no difference in water content of the seeds between imbibing soiutions (Figure 20). Respiration of primed onion seeds. Seeds primed for 2 days in H20, -T.T MPa NaCl or mannitoi soiutions had significantiy higher respiration rates compared to raw seeds (Figure 21). Respiration of seeds primed in H20 was approximateiy 2 times greater than respiration of raw seeds. There were no significant differences in respiration (Figure 21) and water content (Figure 22) between mannitoT and NaCT primed seeds. Effect of duration of priming on respiration. Primed seeds respired more than raw seeds (Figure 23). Increasing the priming 84 .Avmv mcowpww>mu ugmucmum pcmmwggmc mcwm .ooop um coepmnsucw new mcwzom cmpwm muwmm cowco chw_ uwFOmv vmewga ucm Amcw_ cmupouv as; do m_m>mP m>gmmmx noon .w_ aa=m_a 85 02 _ 30w mmhn. < m> .000? um mcov83~0m mzowcm> Cw :o_pwnwnET mc_L:v mummm cowco we mxmba: cmmzxo .m_ aesmwa 87 ZO_._._m_m_>= .6 mm...32=2 can one com new no“ o u u u n u u a u u a/ i ....\a/ \/ L /.\ .. 1/4.\ 4 . é .F .225: 2.5:..- IT - H Go: 2.2...- .m. :2 1 modem.— O«: :0: .3323 2.33:: e . «N (W Mp BIN-Ill“) axvxdn Nl-‘JEMXO 88 .mmpmow—amg q mo mcmmE mcm mw:_m> .UOOF pm mcowp:_0m mcwnwnsw mzovgm> cw cowpwnwnew mcwgzv mvmwm cowco do ucwpcoo Lopez .om mezmwa 89 ZO.._._m_m_>= .5 ww._.32=2 com . cow . com com on: .3252 3:3..- IT H3084 Bu: «2.....- .m. cm... .0. :0330» 9.3.9:: (1M Mp 6/Ju/5w) .|.N3.LNOO HBLVM 90 .mmpmoqumL m mo mamas mcm mos—m> .mpcmspmwcp acmewga mzowcm> cmpmm goo_ pm mvmmm cowco do mxmpa: cmmzxo .FN museum 91 ZO_._._m_m_>= *0 kaDZE‘ Dom an: com DON an: o II- db ‘P J. uh db - (1 d l..\. 8% gm: 1x. .. .3 gm _UmZ an: Sill H e8 a .2255 £2 2%? .. a mod cm; 9.2. a o z .m. 3:258: afiEta (1M MP 5I‘ll-Ill") ENVldn NSSAXO 9?. .mmpmowPamL a do memos mcm mmspm> .mucmEpwwcu mcwewca mzowcm> cmpmm goo? pm mummm cowco mo pcwpcoo Lopez .NN messed 93 com ZO_._._m_m_>= *0 mm._.32:>_ » cow com DON 83 26m .* mod goon .0»: 35.71.: H 93 262 3:53: 25...}? «>8 N. o«: .0. 3:09.33... 9:8...— 9: 66¢ scam 1boo (1M Mp 6/Ju/5w) .l.N‘.-‘LLNOO HBLVM 94 .mmpmowpamg m mo memos mgm mwzpw> .mpcmEpmwgg mcwswga msowcm> Lemma coop pm mummm cowco do mxmpa: comxxo .mm mezmwa 95 ZO_._._m_m.>= .0 mm._.32:2 com cow com cow on. o u u w u u u u . u .5 O X a L. m 3 .6. N n d L. I. V a M .3 3 in, l\\ ml” .3 ... noon 32... IX. F W. a .. :8 a .225: 3.5.? ..T .l. 5 a H 2.2. o 3:53: 25:... .m. a... D. modem. 2.2. o .02. 22...- .6. L. M 3:08.52... 058.... M ‘ G 96 duration from 2 to 6 days did not increase the respiration of mannitol primed seeds. There were no differences in respiration between seeds primed in NaCl or mannitol squtions (Figure 23) or in water uptake among treatments (Figure 24). Pregermination The Effect of Temperature and Dura- tion of Priming and Temperature of Pregermination on Onion Seed RadicTe Length The temperature x duration of priming x temperature of ger- mination interaction was significant for radicIe Iength (Figure 25). Seeds primed at 10°C for 8 days had shortest radicIes of seeds from a1] treatments. Generally, increasing the priming duration and tem- perature produced pregerminated seeds with shorter radicIes. Increasing the priming temperature and duration and pregermi- nation temperature significantiy decreased the time to 50% germination (Figure 26). Seeds took the shortest (1.5 days) to germinate when primed for 8 days at 10°C and pregerminated at 10°C. In contrast, nonprimed, raw seeds pregerminated at 2.5°C took 40 days to reach 50% germination. Percent germination of seeds was not affected by priming duration and temperature and pregermination temperature. Emergence of SeedTings from Raw, Primed, and Pregerminated Onion Seeds SeedIings from pregerminated seeds reached 50% emergence 9.2 days after sowing (TabIe 6). Primed and raw seeds took T3 and 97 .mmgmo..am. q we mcwws mgm mm:_m> .mpcmEpmep ac.E.La mzo.cm> .mpwm 000. pm mvmmm co.:o .o pcmpcoo .mywz .eN aesm.a 98 com ZO_._._m_m.>= .5 mm...Dz:>_ new com com co. . 0 . . u . .u . coon 32. IX. .. 2.2. a 3:53: 2.2...- IT 58 H macaw; 2.30 3:58: 2.5.7 .0. 2:3 0 .902 2:28? .0. 3:08.02... 988.5 53 $8 .68 (1M Mp film/Btu) .LN3.LNOO HBLVM 99 .oom.m op 0mcoame cm..E.m Op mzv czogm yo: m. pamEpmmLp mom>.. oom.m .o o. 0.03 mwczpwcwa50p cowmeWEL0w .cpmcw_ m.o.um. Low mcspmcmaawp newpmcwsgmm >3 UoEwLQ mxwu an m:.E.La we wgsum.0850w .o 80.008.002. zm3-wwgce .mm 0.3... 01 O I ‘ «b l N l d I 100 10°C 25°C RADICLE LENGTHlmmI PREGERMINATION TEMPERATURE |°Cl 10°C __ 10°C 235 C 101 Figure 26. Three-way interaction of temperature of priming x days primed x germination temperature for days to 50% germi- nation. Germination temperatures were 2.5, 5, and ‘ 10°C. b O I VA 102 ‘3‘” i? DAYS TO 50% a GERMINATION #— O ‘2.5'c *1 PREGERMINATION 5,,c TEMPERATURE [°C] 10°C \ 25°C 5°C 10 5 \ 5°C , .\ s’c loo '2. 3 \OR‘MED 103 Tabie 6.--Emergence of seediings from raw, primed, and primed- pregerminated onion seeds. Days to 50% Spread of Percenty Treatments Emergence Emergence (days) Emergence Primed- pregerminated 9 aX 2.4 a 77 a Primed 13 b 2.4 b 75 a Raw seed 15 c 44.0 c 74 a XMeans within coiumns separated by Duncan's muitipie range test, at 5% level. '1. o o o y(arcsin)2 transformation used for ana1y51s of variance. 15 days to 50% emergence, respectiver. Pregerminated seeds produced the most uniform seedTing emergence (lowest spread of germination) compared to primed and raw seeds. Pregermination and priming had no effect on percent emergence. Discussion and Summary Seeds primed in -I.T MPa mannitoI or NaCT for 8 days at 10°C germinated faster and more uniforme than seeds primed with other treatments, without reducing totaI germination (TabIe 5). However, PEG 6000 was not as safe as mannitoI or NaCl for priming onion seeds, since totaI germination was reduced after 48 hr of priming (TabIe 3). The reduction in germination of onion seeds primed in PEG 6000 may have been due to an insufficient oxygen suppIy in the priming squ- tion. At 10°C, oxygen is 69% Tess avaiIabTe in -I.T MPa PEG 6000 104 than in water (73). This low oxygen level may have induced anaerobio- sis in some seeds. Anaerobic seeds accumulate ethanol which is toxic to the cells of the seed and may eventually lead to seed death (70). Furthermore, the high viscosity (4.91 centipose) of -l.l MPa PEG 6000 makes it difficult to aerate, resulting in poor oxygen dispersion (73). Osmotic potentials of -l.l, -l.3, and -l.7 MPa did not affect the num- ber of days to 50% germination or total germination of onion seeds (Table 4). However, increasing the osmotic potential of the priming solution lengthened the number of days to 3 to 4% germination. Thus, the lowest osmotic potential, -l.l MPa, was utilized priming the onion seed. Seeds primed at l0°C in NaCl or mannitol at all osmotic poten- tials and durations germinated faster and more uniformly than seeds primed at 24°C (Table 4). At 10°C, seeds required 8 days of priming to reach 3 to 4% germination, but required only 4 days of priming at 24°C. However, l0°C-primed seeds germinated faster and more uniformly, with greater total germination than 24°C-primed seeds after drying and rehydrating (Table 4). A possible explanation for these germination differences is that 24°C-primed seeds may have been exposed to anaero- bic conditions. Seeds primed at 24°C apparently respire at a greater rate than at l0°C and oxygen availability for the seeds may have been inadequate (9l). Thus, seeds primed at 24°C may have been injured or killed during priming by anaerobiosis which resulted in slower and reduced total germination in comparison to 10°C-primed seeds (Table 4). Priming seeds for 8 days resulted in faster and more uniform germination after drying and rehydration than priming for shorter \- 105 periods (Figures l0, ll). Many seeds germinated on the ninth day, indicating that most of the seeds had reached maximum priming in 8 days. Priming durations less than 8 days may not have brought the seeds up to a point just prior to germination, and upon rehydration they germinated slower and less uniformly than 8-day-primed seeds. Seeds primed for 2 days used more oxygen than raw seeds dur- ing 5 hr of imbibition at l0°C (Figure 2l). Priming may have caused seeds to accumulate biochemical compounds required for germination, thus speeding the respiration process after imbibition. For instance, primed seeds are known to contain greater quantities of ribosomal RNA than raw seeds; ribosomal RNA is essential in the production of various compounds such as enzymes necessary for seed germination. Increasing the priming duration to 6 days, however, did not signifi- cantly increase oxygen uptake (Figure 23). Evidently, oxygen uptake of seeds was at maximum after 2 days of priming. Primed seeds emerged faster than raw seeds and therefore would be expected to utilize more food reserves during germination (Table 6). However, there were no differences in food reserve utili- zation between primed and raw seeds during priming and l0 days of germination (Figures l7, 18). It appears that food reserve depletion is not a limiting factor in priming or pregermination processes. Leakage studies confirmed that increased speed and uniformity of germination of primed seeds was not a result of weakening the seed coat. If seed coats were weakened by priming, leakage rates would have been greater during reimbibition. However, primed seeds leaked at a lower rate than nonprimed seeds (Figure l2). Two explanations 106 are plausible: (l) cellular and subcellular membranes may have become more organized during priming, thereby reducing solute leak- age during rehydration; (2) leachable solutes were leached-out during priming so that solute leakage was reduced during rehydration. In addition to priming temperature, duration, and solute, temperature of germination affects radicle length (Figure 23). Ger— mination of primed seeds at 10°C resulted in short radicles and reduced the number of days to 50% germination in comparison to ger- mination at 2.5 and 5.0°C (Figures 25, 26). Germination at 10°C appeared to have continued the same process as priming at l0°C, which produced faster and more uniformly germinating seeds. This study shows that 2 methods could be used to improve the speed and uniformity of emergence of onion seedlings under cold soil conditions in the field: (I) priming seeds in -l.l MPa NaCl or manni- tol for 8 days at 10°C offers the advantage of greater speed and uni- formity of emergence of seedlings in comparison to raw seeds (Table 6). An added advantage of using primed seeds is that a conventional seeder could be used; (2) these primed seeds could be germinated at l0°C in H20 for 2 days to obtain pregerminated seeds with short, uniform radicles. Pregerminated seeds emerge with even greater speed and uniformity than primed and raw seeds (Table 6). A fluid drill planter could be used to sow these pregerminated seeds, since the seeds' radicles are short and would not be damaged during sowing. The major findings of this study are summarized as follows. l07 Priming Onion Seeds There were no differences between solutes used for priming, except for PEG 6000, which reduced germination. Osmotic potentials of -l.l to -l.3 MPa for 8 days at 10°C were optimal for priming onion seeds. Leakage Studies Leakage from onion seeds was reduced after priming. Food Reserve Utilization Studies There were no changes in food reserves of onion seeds during priming. Food reserve utilization was similar for primed and raw seeds during germination. Respiration Studies Primed seeds had higher respiration rates than raw seeds after inbibition in water at 10°C. There is a limit to the increase in respiration obtained by priming. Pregermination Studies Temperature and duration of priming and temperature of pre- germination affected radicle length. Priming for 8 days at 10°C and germinating at l0°C reduced radicle length fourfold over l0°C germi- nated controls. Pregerminated seeds emerged earlier and more uni— formly at 10°C than primed and raw seeds. BIBLIOGRAPHY 108 10. 11. BIBLIOGRAPHY A-As Sagui, M. and A. Corleto. 1978. 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