Matric and osmotic priming of Echinacea purpurea (L.) Moench seeds

Matric and osmotic priming of Echinacea purpurea (L.) Moench seeds

SClEIITIA HORTICULTUM ELSEVIER Scientia Horticulturae 59 (1994) 37-44 Matric and osmotic priming of Echinacea purpurea (L.) Moench seeds 1 W.G. Pill...

459KB Sizes 0 Downloads 80 Views

SClEIITIA HORTICULTUM ELSEVIER

Scientia Horticulturae 59 (1994) 37-44

Matric and osmotic priming of Echinacea purpurea (L.) Moench seeds 1 W.G. Pill*, C.K. Crossan, J.J. Frett, W.G. Smith DelawareAgriculturalExperiment Station, Department of Plant and Soil Sciences, Collegeof Agricultural Sciences, Universityof Delaware, Newark, DE 19717-1301, USA Accepted 22 March 1994

Abstract Purple coneflower seeds (Echinacea purpurea (L.) Moench ) following osmotic priming in polyethylene glycol (PEG) or matric priming in expanded vermiculite had greater rate, synchrony and percentage of germination at 20 °C than non-primed seeds. Osmotic or matric priming for 10 days at - 0 . 4 MPa and 15 °C resulted in higher germination rate and percentage than shorter (5 day) exposure or lower ( - 1.5 MPa) water potential. Seedling emergence rate, synchrony and percentage from osmotically or matrically primed seeds were similar in both cool (23-27°C day) and warm (35-40°C) glasshouse regimes. Emergence was faster from primed than from non-primed seeds in both regimes. Emergence percentage was higher (80%) from primed seeds than from non-primed seeds (50%) in the cool regime but emergence synchrony was unaffected. In the warm regime, primed seeds emerged more synchronously than non-primed seeds but emergence percentage was unaffected. Moistened vermiculite substituted for PEG solution as a priming medium for purple coneflower seeds since benefits to seed germination or seedling emergence following priming ( - 0.4MPa, 15 oC, 10 days, darkness) in these media were similar. Keywords: Wild flowers; Purple coneflower; seed treatment

1. Introduction Purple coneflower (Echinacea purpurea (L.) Moench), a member of the Asteraceae family that is native to North America, is used in wild flower meadows, *Correspondingauthor. ~Miscellaneous Paper No. 1487 of the Delaware Agricultural Experiment Station, Contribution No. 313 of the Department of Plant and Soil Sciences. 0304-4238/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSD10304-4238 ( 94 ) 00654-X

38

W.G. Pill et al. /Scientia Horticulturae 59 (1994) 37-44

perennial gardens, and as a cut flower. However, seeds of this species display low germination percentage, delayed germination and wide variation in emergence rate which reduce the uniformity of seedling stands (Atwater, 1980). For instance, purple coneflower field emergence was less than 10% (Smith-Jochum and Albrecht, 1987) and seedling emergence in the greenhouse reached only 21% (Finnerty and Zajicek, 1992) or 39% (Samfield etal., 1991 ). The limitations to seed propagation of Asteraceae species are attributable, at least partly, to a semipermeable inner membranous seed coat that may restrict water and oxygen passage to the embryo and prevent leaching of inhibitors from the cotyledons (Atwater, 1980; Wareing and Saunders, 1971 ). Germination procedures for purple coneflower include moist stratification at 19-24°C for 4 weeks (Phillips, 1985) or 1 month stratification at 0°C in sphagnum peat moss or sand (Smith-Jochum and Albrecht, 1987). Priming purple coneflower seeds in 50 mM potassium phosphate buffer (pH 7) improved germination rate and percentage (Samfield etal., 1990, 1991; Finnerty and Zajicek, 1992). Osmotic priming permits partial seed hydration so that pregerminative metabolic activities proceed but germination is prevented. Enhanced vigor of primed seeds compared to non-primed seeds increased the rate, synchrony and percentage of seedling emergence under such adverse seed-bed conditions as low temperature (Pill and Finch-Savage, 1988 ), high temperature (Carpenter, 1989, 1990), reduced water availability (Frett and Pill, 1989) or salinity (Pill etal., 1991). Matric priming, a newer technique than osmotic priming involving seed hydration in solids containing limited amounts of water or aqueous solution, has been reviewed (Khan, 1992; Pill, 1994). Seed matric priming in synthetic silicate (Micro-Col E; Manville, Denver, CO) increased the seedling emergence rate and percentage of carrot, tomato and pepper (Khan et al., 1992). Priming primula and impatiens seeds in Micro-Col E increased seedling emergence rate and shoot fresh weight, but had no effect on percentage emergence (Khan et al., 1990). The present study was undertaken to compare the effects of osmotic or matric priming on purple coneflower seed germination and seedling emergence. 2. Materials and methods

2.1. Duration and water potential of priming treatments Seeds of purple coneflower (Echinacea purpurea (L.) Moench ), acquired from The Vermont Wildflower Farm (Charlotte, VT), were primed at 15 °C in darkness for 5 or 10 days at - 0 . 4 MPa or - 1.5 MPa created osmotically with polyethylene glycol (PEG) 8000 or matrically with moistened expanded vermiculite No. 5 (W.R. Grace, Cambridge, MA). The - 0 . 4 and - 1.5 MPa, respectively, were created by adding 161 g and 342 g PEG 1-1 water (Michel, 1983), or by adding 100% and 50% (w/w) water to vermiculite (Khan et al., 1990, 1992). The osmotic priming treatments were carded out in 125 ram× 80 m m × 20 mm

W.G. Pill et al. / Scientia Horticulturae 59 (1994) 37-44

39

transparent polystyrene boxes containing two layers of germination paper (Seed Germination Blotters No. 385; Seedburo, Chicago, IL) moistened with 15 ml of the PEG solution. Each of the five replicated boxes contained 100 seeds. For matric priming, 250 seeds were added to 17.5 g vermiculite that had received 17.5 g water ( - 0 . 4 MPa) or 8.75 g water ( - 1.5 MPa) in 207 ml plastic drinking cups. The weight ratios of seed:vermiculite:water were 1:20:20 for - 0 . 4 MPa and 1:20:10 for - 1.5 MPa. The seeds, water and vermiculite were mixed thoroughly by stirring. Aluminium foil placed over the cup top and secured with a rubber band minimized evaporative loss. Priming treatments were scheduled so that all germination tests started at the same time. Following priming, the seeds and priming agent were washed into a sieve that retained the seeds. The seeds were rinsed thoroughly with running demineralised water to remove the PEG or vermiculite, and 100 seeds were transferred into 125 m m × 80 m m × 20 m m boxes containing two layers of germination paper moistened with 15 ml of 0.5-fold Hoagland solution (Hoagland and Arnon, 1950). Non-primed seeds were included in the germination tests as controls. Germination tests were conducted at 20°C in darkness. The numbers of seeds germinated (having visible radicles ) were recorded daily until no further germination occurred. From these data, the angular transformation of the final germination percentage (FGP), days to 50% FGP (Gso, an inverse measure of germination rate ), and days between 10% and 90% FGP (G~o_ 90, an inverse measure of germination synchrony) were calculated and subjected to analysis of variance.

2.2. Emergencefrom primed seeds in the glasshouse Seeds were osmotically or matrically primed ( - 0 . 4 MPa for 10 days at 15 °C) as described previously. Only 100 seeds were matrically primed in each cup, but the 1:20:20 seed:vermiculite:water ratio was retained. The primed seeds were rinsed of their priming agents, allowed to dry for 2 days (18°C, 40% relative humidity). These seeds and non-primed seeds were sown into proprietary peatlite (Promix BX; Premier Brands, New Rochelle, NY) contained in 17 cm × 12 cm × 6 cm plastic flats. Each treatment (flat) consisted of 100 seeds sown in five furrows 1 cm deep and 12 cm long. The seeded furrows were covered with 1 cm depth of peat-lite and the flats were surface irrigated. One-half of the flats for each of the four replications was placed on electrical heating mats and covered with a transparent polyethylene tent to create a warm regime (35-40 ° C day, 21-24 ° C night). The other half of the flats of each replication was placed directly on the glasshouse bench and not covered with polyethylene to create a cool regime (2327°C day, 17-21 °C night). The 3 (seed t r e a t m e n t ) × 2 (temperature regime) factorial was replicated four times in randomized complete block design. The study was conducted under natural light (July-August). The numbers of seedlings emerged (hypocotyl arch visible) were recorded daily until no further emergence occurred. From these data, the angular transformation of the final emergence percentage (FEP), days to 50% FEP (Eso, an inverse

40

W.G. Pill et al. / Scientia Horticulturae 59 (1994) 37-44

measure of emergence rate), and days between 10% and 90% FEP (Elo_9o , a n inverse measure of emergence synchrony) were calculated and subjected to analysis of variance. Shoots were cut at the peat-rite surface 20 days after sowing and shoot dry weights (65"C for 1 week) were determined. 3. Results and discussion

3. I. Duration and water potential of priming treatments

Relative to the response of non-primed seeds, priming increased germination rate (decreased Gso), generally increased FGP, but had no effect o n Glo-9o (Table 1 ). Apart from generally lower Gso values with matric than with osmotic priming, priming agent had no effect on seed germination. The less negative water potenTable 1 Final germination percentage (FGP) and its angular transformation [deg.], days to 50% of FGP (Gso), and days between 10% and 90% ofFGP (G1o-9o) of purple coneflower seeds at 20°C in darkness as affected by the water potential and duration of osmotic (PEG) and matric (VER) priming

Priming agent

Priming potential (-MPa)

Priming duration (days)

Gso (days)

PEG

0.4 0.4 1.5 1.5

5 10 5 10

3.5 2.5 4.0 3.3

VER

0.4 0.4 1.5 1.5

5 10 5 10

Glo-90 (days)

FGP %

deg.

6.3 3.9 6.7 6.6

61 57 58 61

[51] [49] [50] [52]

3.1 2.5 3.4 2.7

6.0 4.2 6.6 4.7

61 63 57 60

[51 ] [53] [49] [51]

Non-primed seeds LSDo.os (one-way)

4.7 0.5

6.5 2.0

54

[47] [5 ]

Significances Priming agent (A) Priming potential (P) A× P Priming duration (D) A×D PXD A×PXD Primed seeds vs. non-primed seeds

*** *** NS *** NS NS NS ***

NS * NS ** NS NS NS NS

I_~D, least significant difference; NS, not significant. *'**'***Significantat P ~ 0.05, P~<0.01 or P~< 0.001, respectively.

NS NS NS NS NS NS NS *

W.G. Pill et al. / Scientia Horticulturae 59 (1994) 37-44

41

tial and the longer priming duration generally led to lower Gso and Glo-9o values. Thus, 10 day exposure to - 0 . 4 MPa at 15°C was selected as the priming treatment for the subsequent study. Since the response to a given priming treatment can vary between seed lots of the same cultivar (Brocklehurst et al., 1984), the optimum priming treatment (priming agent, water potential, temperature, duration) for a given seed lot is determined by trial and error (Bradford, 1986). Samfield et al. (1991) noted that whilst the percentage germination or emergence of purple coneflower was unaffected by priming osmotic potential (0, - 0.39, or - 0.77 MPa from 0, 50, or 100 mM potassium phosphate pH 7 buffer at 16°C, respectively), priming duration had an effect. Six to 9 days was optimal, 3 days delaying germination and 12 days reducing final germination or emergence percentage. Lowering the priming temperature below 15 ° C used in our study may prove beneficial since 1 month stratification in peat at 0°C increased germination rate and percentage of purple coneflower seeds (Smith-Jochum and Albrecht, 1987). Although the initial matric potentials of the water-vermiculite mixture in our study were nominally - 0 . 4 and - 1.0 MPa as established by moisture characteristic curves (Khan et al., 1990, 1992), actual matric potential values undoubtedly decreased during priming owing to water imbibition by the seeds and to a small amount of evaporative loss. However, since the expanded vermiculite has a high water-holding capacity, a small decrease in water content would not influence the matric potential greatly. Ten percent water loss (dry weight) would lower the matric potential by 0.1 MPa at - 0 . 4 MPa, and by 0.4 MPa at - 1.0 MPa. In the only known report of matric priming of seeds of ornamental plants (Khan et al., 1990), primula and impatiens emergence rates and shoot fresh weights were increased, but emergence percentages were unaffected by priming in synthetic silicate (Miero-Cel E) at - 0 . 1 MPa for 9 days at 15°C. Rate, synchrony and percentage germination of purple coneflower seeds were increased by matric priming in our study.

3.2. Emergencefrom primed seeds in the glasshouse Both osmotic and matric priming similarly improved seedling emergence in the glasshouse (Table 2 ). Seedling emergence was fasterfrom primed seeds than from non-primed seeds under both glasshouse temperature regimes, although the Eso was lower in the warm regime (5.I days) than in the cool regime (2.8 days). Priming eliminated Eso differencesdue to temperature regime. While emergence synchrony was unaffected by priming in the cool regime, primed seeds had lowcr E~o-9o than non-primed seeds in the warm regime. Final emergence percentage was an average 22 percentage points greater from primed seeds (80%) than from non-primed (58%) in the cool regime, but the average 31% FEP was unaffected by seed treatments in the warm regime. Priming increased the rate,synchrony and percentage germination/emergence of carrot at low temperatures (Pilland Finch-Savage, 1988 ) and of impatiens at low temperatures and reduced water availability (Frett and Pill, 1989). How-

42

W.G. Pill et al. /Scientia Horticulturae 59 (1994) 37-44

Table 2 Final emergence percentage (FEP) and its angular transformation [ deg. ], days to 50% of FEP (Eso), days between 10% and 90% of FEP (Ego-too), and shoot dry weight (20 days after sowing) from osmotically (PEG) or matrically (VER) primed ( - 0 . 4 MPA, 15°C, 10 days) seeds of purple coneflower in the glasshouse Seed treatment PEG VER

Emergence temperature

( days )

Elo-9o (days)

Shoot dry weight (rag per shoot )

FEP %

[deg. ]

Cool

7.3 7.2 10.0

5.4 5.5 7.7

81 78 58

[64] [62] [50]

15.2 15.8 11.1

Warm

7.4 8.0 12.8

5.2 7.1 10.5

32 35 27

[34] [36] [31 ]

12.3 12.0 8.6

1.7

3.2

[7 ]

2.9

Non-primed PEG VER

Eso

Non-primed LSDo.o5 (two-way)

Significances Seed treatment (S) Emergence temperature (T) S×T

*** * NS

* NS NS

** *** NS

*** *** NS

NS, not significant; LSD, least significant difference. *P~<0.05; **P~<0.01; ***P~<0.001.

ever, the temperatures used in these studies (5 ° C and 12.5 ° C, respectively) were lower than the 23-27 °C day, 17-21 °C night of our cool regime. Higher rate and synchrony of emergence from primed than from non-primed seeds in the warm regime (35-40°C day, 21-24°C night) was reported for primed seeds of dusty miller (Carpenter, 1990), Salvia splendens (Carpenter, 1989) and pansy (Carpenter and Boucher, 1991 ) germinated at above 30 oC. Unlike purple coneflower, these ornamental species had higher germination percentage at high temperatures as a result of priming. Finnerty and Zajicek (1992) found that osmotic priming increased emergence of purple coneflower from 21% (non-primed seeds ) to 47% in a glasshouse with 28 oC/18 oC (day/night). The greater seedling shoot dry weight from primed than from non-primed seeds 20 days after sowing at both temperature regimes (Table 2) is in agreement with the greater seedling height from primed purple coneflower seeds than from nonprimed seeds (Samfield et al., 1991 ). Increased seedling growth from primed seeds resulted from more rapid seedling emergence (Pill, 1986; Pill et al., 1991 ) and not from increased relative growth rate, at least in leek (Brocklehurst et al., 1984). Finnerty and Zajicek ( 1992 ) noted that osmotic priming increased purple coneflower seedling root dry weight, but not shoot dry weight. Our results have shown that matric priming in expanded vermiculite was as effective as osmotic priming in PEG in improving seed germination or seedling emergence of purple coneflower. The problem of high viscosity and low oxygen

W.G. Pill et aL / Scientia Horticulturae 59 (1994) 37-44

43

solubility in an osmoticum such as PEG (Mexal et al., 1975) can be overcome by conditioning seeds in a relatively inert, water-insoluble carrier such as expanded vermiculite. Expanded vermiculite as the priming agent for wild flowers is particularly advantageous for broadcast sowing since seeds would not have to be separated from the vermiculite. Following seed priming in vermiculite, more vermiculite could be added to increase the bulk volume and aid uniformity of seed dispersal. Since the seeds and vermiculite are of similar density, minimal separation of the two would be expected at the time of seed broadcasting.

Acknowledgment The authors are grateful to the Perennial Plant Association, Hillard, OH, for providing partial funding in support of this research.

References Atwater, B.R., 1980. Germination, dormancy and morphology of the seeds of herbaceous ornamental plants. Seed Sci. Technol., 8: 523-573. Bradford, K.J., 1986. Manipulation of seed water relations via osmotic priming to improve germination under stress conditions. HortScience, 21:1105-1112. Brocklehurst, P.A., Dearman, J. and Drew, R.L.K., 1984. Effects of osmotic priming on seed germination and seedling growth in leek. Scientia Hortic., 24:201-210. Carpenter, W.J., 1989. Salvia splendens seed pregermination and priming for rapid and uniform plant emergence. J. Am. Soc. Hortic. Sci., 114: 247-250. Carpenter, W.J., 1990. Priming dusty miller seeds: role of aeration, temperature, and relative humidity. HortScience, 25: 299-302. Carpenter, W.J. and Boucher, J.F., 1991. Priming improves high-temperature germination of pansy seed. HortScience, 26: 541-544. Finnerty, T. and Zajicek, J.M., 1992. Effects of seed priming on plug production of Coreopsis lanceolata and Echinacea purpurea. J. Environ. Hortic., 10:129-32. Frett, J.J. and Pill, W.G., 1989. Germination characteristics ofosmotically primed and stored Impatiens seeds. Sci. Hortic., 40: 171-179. Hoagland, D.R. and Arnon, D.I., 1950. The water-culture method for growing plants without soil. California Agricultural Experiment Station Circular 47. Khan, A.A., 1992. Preplant physiological seed conditioning. Hortic. Rev., 13:131-181. Khan, A.A., Miura, H., Prusinski, J. and Ilyas, I., 1990. Matri-conditioning of seeds to improve emergence. Proceedings National Symposium on Stand Establishment of Horticultural Crops, Minneapolis, MN, pp. 19-40. Khan, A.A., Maguire, J.D., Abawi, G.S. and Ilyas, S., 1992. Math-conditioning of vegetable seeds to improve stand establishment in early field plantings. J. Am. Soc. Hortic. Sci., 117:41-47. Mexal, J., Fisher, J.T., Osteryoung, J. and Reid, C.P.P., 1975. Oxygen availability in polyethylene glycol solutions and its implications in plant-water relations. Plant Physiol., 55: 20-24. Michel, B.E., 1983. Evaluation of the water potentials of solutions of polyethylene glycol 8000 both in the absence and presence of other solutes. Plant Physiol., 72: 66-70. Phillips, H.R., 1985. Growing and Propagating Wild Flowers. University of North Carolina Press, Chapel Hill. Pill, W.G., 1986. Parsley emergence and seedling growth from raw, osmoconditioned and pregerminated seeds. HortSeience, 21:1134-1136.

44

W.G. Pill et al. / Scientia Horticulturae 59 (1994) 37-44

Pill, W.G., 1994. Low water potential and presowing germination treatments to improve seed quality. In: A.S. Basra (Editor), Seed Quality: Basic Mechanisms and Agricultural Implications. Haworth Press, Binghampton, NY. Pill, W.G. and Finch-Savage, W.E., 1988. Effects of combining priming and plant growth regulator treatments on the synchronisation of carrot seed germination. Ann. Appl. Biol., 114: 383-389. Pill, W.G., Frett, J.J. and Morneau, D.C., 1991. Germination and seedling emergence of primed tomato and asparagus seeds under adverse conditions. HortScience, 26:1160-1162. Samfield, D.M., Zajicek, J.M. and Cobb, B.G., 1990. Germination of Coreopsis lanceolata and Echinacea purpurea seeds following priming and storage. HortScience, 25:1605-1606. Samfield, D.M., Zajicek, J.M. and Cobb, B.G., 1991. Rate and uniformity of herbaceous perennial seed germination and emergence as affected by priming. J. Am. Soc. Hortic. Sci., 116: 10-13. Smith-Jochum, C.C. and Albrecht, M.L., 1987. Field establishment of three Echinacea species for commercial production. Acta Hortic., 208:115-122. Wareing, P.E. and Saunders, P.R., 1971. Hormones and dormancy. Annu. Rev. Plant Physiol., 22: 261-288.