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William J. Carpenter

Priming permits seeds to slowly imbibe water at regulated rates and to begin the initial stages of germination. Hypertonic polyethylene glycol (PEG) 8000 solutions of 1.0 and 1.2 MPa at 15C improved seed germination of dusty miller (Senecio cineraria DC.). At 0.8 MPa, germination was promoted during priming. No differences in rates, span, or total germination were found among seeds primed for 1, 2, or 3 weeks with or without aeration during priming. Germination percentages of primed and nonprimed seeds were similar at 10, 15, 20, and 25C, but 42% to 81% higher for primed seed at 30 or 35C. Priming reduced days to 50% of total germination (T50) 23% to 61%, and germination spans in days 30% to 67%. Primed seeds germinated most rapidly and uniformly at 20 and 25C. No change in total germination, T50, or germination span resulted when moisture contents of primed seeds were lowered to 7.8% or seeds were held at –80C for 7 days. Primed seed performance was unchanged after storage at 5C and 52% RH for 16 weeks.

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William J. Carpenter

Caladium hortulanum Birdsey cv. Candidum seed failed to germinate without light; maximum germination required daily, incandescent light of ≤4 hours. Lengthening daily lighting periods progressively reduced the days to 50% relative germination (T50) from 20 to 8, and days between 10% and 90% relative germination (T90 – T10) from 16 to 5. T50 and T90 – T10 were shortest (≈ 8 days) at 25 and 30C, while total or absolute germination percentage (G) was highest at ≈ 90%. G was 94% for seeds harvested immediately, but 75% or 38% for seeds that remained in fruits for 3 or 12 weeks after fruit abscission from the spadix. Total absolute germination was reduced from 95% to 87% when seed moisture contents declined to <14%. Seed storage for 7 days at from 10 to – 80 C-caused no reduction in G. Seeds were stored 6 months at 15C and 22%, 33%, or 52% RH without change in G, but storage at 5 or 25C and 11%, 75%, or 95% RH significantly reduced germination.

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William J. Carpenter and Susumu Maekawa

Verbena (Verbena × hybrida Voss) seed germination varied with the water content of the substrate. Total germination percentages (G) were highest when substrates were 75% to 100% saturated and progressively declined with increased free distilled water (FDW) on the blotter paper substrate. Natural differences in G among cultivars at favorable substrate moisture levels increased when free water was present. Removing the seed hilums did not increase G of `Romance Scarlet' on a substrate with FDW, but significantly increased the G of `Showtime Blaze' and `Red A'. Au inverse relationship was found between seed moisture contents and G at high substrate moisture levels. `Romance Scarlet', `Showtime Blaze', and `Red A' had 64%, 73%, and 84% seed moisture contents and G of 72%, 18%, and l0%, respectively. The period of sensitivity to excessive water during germination was day 2 for `Red A' and days 2 and 3 for `Showtime Blaze'. The G of `Romance Scarlet' seed was not reduced when placed on a substrate containing FDW for 1 day. Removal of seed hilums from `Red A' significantly increased G during day 2 for seeds on a substrate containing FDW.

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Susumu Maekawa and William J. Carpenter

The germination of verbena (Verbena × hybrids) seed was found to be sensitive to high substrate moisture content. Cultivars varied in sensitivity to excessive substrate moisture content, with `Romance Scarlet' having higher total germination (G) in the presence of free water than `Showtime Blaze' or seedling `Red A'. Hilum cavity measurements of dry seeds showed larger hilum apertures with reduced depths for seeds of `Romance Scarlet' than for the others. Seed imbibition resulted in a rapid and extensive thickening of the hilum wall. The extent of hilum aperture closure varied among cultivars and the quantity of water present. Free water reduced hilum apertures 45% for `Romance Scarlet', 60% for `Showtime Blaze', and 86% for `Red A'. Seeds of `Romance Scarlet' and `Showtime Blaze' failed to germinate with lanolin covering the hilum, while seeds coated with lanolin, except for the hilum, had 67% to 78% G of nontreated seeds. This difference indicates that essential oxygen for the embryo was obtained through the hilum and micropyle of the seeds. Total germination varied with substrate moisture content, with seeds placed horizontally on 2%, 1%, or 0.5% agar having 80%, 75%, and 65% germination, respectively, for `Romance Scarlet' and 59%, 41%, and “24%, respectively, for `Showtime Blaze'.

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William J. Carpenter and Joseph F. Boucher

The optimum conditions for priming pansy (Viola × wittrockiana) seeds were in aerated osmotic solutions of polyethylene glycol 8000 (PEG 8000) at – 1.0 MPa for 7 days at 15C. Priming at – 0.8 MPa and 15C caused 8% to 26% of seeds to germinate during 4 to 13 days of priming. Increasing numbers of abnormal seedlings developed when priming was extended beyond 7 days. Final germination percentages were better in laboratory studies at 35C for primed (51%) than nonprimed (10%) seeds. Removal of the mucilage released by the seed with 240 g KOH or 170 g NaOH/liter for 15 or 30 seconds during priming did not affect total germination percentages, but did improve seed handling. Primed seed had higher, faster, and more uniform germination than nonprimed seeds after sowing in growing medium in plant growth chambers or greenhouses.

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William J. Carpenter and Eric R. Ostmark

The storage and germination environments were evaluated to determine the cause of low total germination percentages and highly irregular germination of Coreopsis lanceolata L. seed. Highest total germination and most rapid and uniform germination of seed occurred at constant 15C, other constant temperatures and all alternating temperature regimes caused lower total germination or delayed it. Seeds tolerated -20C during storage, but total germination was reduced below -5C. Recently harvested seeds had 44% total germination, but 54% to 81% germination was achieved after 6 hours of soaking seeds in 1000 ppm GA3, 1000 ppm ethephon, or 25 ppm kinetin alone or in combination. Growth regulators reduced the number of days to 50% of final germination (T50), and the span in days between 10% and 90% of germination (T90 - T10). Storing fresh seeds without chemical treatment for > 6 months at 5C and 10% to 20% relative humidity (RH), or 15C at 20% to 35% RH, increased total germination to 75% and 80%, respectively. Ten days were required to achieve T50 after 5 to 6 months of storage at 5C and 10% to 20% RH or 15C and 10% to 40% RH, with longer periods to T50 at other storage durations and RH levels. The germination spans (T90 - T10) were lengthened the higher the seed storage temperatures between 5 to 25C, with longer spans as seed storage durations and relative humidities increased. Total germination was similar after storing seeds at 5 or 15C and 10% to 30% RH and after soaking recently harvested seeds in GA3 + ethephon, but the days to T50 and T90 - T10 were shorter after growth regulator treatment. Chemical names used: (2-chloroethyl) phosphonic acid (ethephon); gibberellic acid (GA3); 6-furfurylaminopurine (kinetin).

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Gamil A. Kabbabe and William J. Carpenter

Verbena seed when harvested, has a natural dormancy that gradually dissipates during a 5 to 8 month period of dry storage. In this study, the gradual loss of the dormancy causing factor was correlated with germination percentage. Acetone treatment of verbena seeds was found to cause a slight, but non-significant, reduction in total germination. However, the infusion of gibberellic acid (GA4/7) and kinetin (KIN) with the acetone at various concentrations improved germination. The traditional method of seed osmoconditioning using Polyethylene Glycol (PEG 8000) at -1.0 MPa caused a non-significant reduction in percent germination, similar to that with acetone. When growth regulators were mixed with the osmoconditioning solution, at the concentrations used with acetone, a definite and significant improvement in terms of rate and percent of germination was observed.

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William J. Carpenter and Joseph F. Boucher

Delphinium seed germination was about equal in light or darkness. Seed total germination percentages were highest and about equal at constant 15 or 20C and alternating (12 h) 10/20C, 15/25C, or 20/30C. The most rapid and uniform germination generally occurred at constant 20C. Storing seeds dry at 2C for 3 weeks before germination reduced the days to 50% of final germination (T50) and between 10% and 90% germination (T90 - T10) but did not increase total germination. The seeds had only limited desiccation tolerance, with `Magic Fountains Lavender' having declining germination percentages at moisture contents below 7.0% and `Magic Fountains Lilac' below 6.7%. Seeds tolerated storage at low, nonfreezing or subzero temperatures, but cultivar responses differed. `Magic Fountains Lavendar' had progressively lower germination percentages as storage temperatures declined from 5 to –20C, while `Magic Fountains Lilac' germination increased. The relative humidity (RH) and temperature that delphinium seed received during long-term storage influenced germination. Germination after seed storage at 5C was higher, earlier, and more uniform than after 15 or 25C storage. The highest total germination percentages occurred following seed storage at 5C and 30% to 50% RH, the shortest T50 from 35% to 55% RH, and shortest spans (T90 - T10) from 25% to 50% RH.

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William J. Carpenter and Joseph F. Boucher

Light, temperature, relative humidity (RH), and GA3 affect vinca [Catharanthus roseus (L.) G. Don] seed storage and/or germination. GA3 failed to increase the germination percentage in darkness but significantly increased the percentage in continuous light. Similarly, GA3 treatment reduced both the number of days required to achieve 50% of the final germination percentage (T50) and the span between 10% and 90% germination (T90 — T10) for seeds in light, but not in darkness. Germination percentages were maximal and about equal at 25, 30, or 35C in darkness; germination was lowest below 25C. Germination T50 and T90 — T10 required the fewest days between 25 and 35C. Reducing seed moisture from 9.9% to 3.9% increased the T50 from 2.4 to 3.0 days but failed to change germination percentages. Germination percentage declined linearly as seed storage temperatures were reduced from 5 to — 20C, whereas days to T50 increased. Seed storage for 12 months without reduction in germination percentage was possible at 5C and 11%, 33%, or 52% RH, but storage at 75% or 95% RH for periods exceeding 1 month reduced germination. Seeds stored at 33% or 52% RH required fewer days to T50 than did seeds stored at 11%, 75%, or 95% RH. Chemical name used: gibberellic acid (GA3).

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William J. Carpenter, Eric R. Ostmark and John A. Cornell

The role of light on phlox germination and radicle emergence was studied. Neither light level nor duration affected total germination (G) percentages, which ranged from 93%. to 98%. Increasing light level and lengthening light duration delayed achieving 50% of final germination (T50) and increased the span in days between 10% and 90% germination (T90 - T10). Increasing light duration from 0 to 24 hours during germination at 0.15 μmol·s-1·m-2 progressively increased T50 from 3.5 to 7.1 days and T90 - T10 from 2.6 to 13.1 days. Similarly, lengthening light duration from 0 to 24 hours at 1.5 μmol·s-1·m-2 light increased T50 from 3.7 to 10.8 days and T90 - T10 from 2.8 to 13.4 days, whereas 15 μmol·s -1·m-2 increased T50 from 3.9 to 21.9 days and T90 - T10 from 2.9 to 29.2 days. Increasing the number of days in darkness from 0 to 6 decreased T50 from 14.8 to 4.3 days and T90 - T10 from 20.2 to 3.5 days. Increasing the number of days in light from O to 6 increased T50 from 4.0 to 8.9 days and T90 - T10 from 3.8 to 8.2 days. Estimated rates of decline or increase in T50 and T90 - T10 with each added day in darkness or light were measured by fitting regression equations. Seeds germinated in continuous darkness or in 24 or 48 hours of light followed by total darkness had similar G, T50, and T90 - T10. The results indicate that initial phlox seed germination was not affected by light, but that light inhibited radicle extension in later germination stages.