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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).
Abstract
Amaryllis, (Hippeastrum × hybridum Hort.) seed germination was light-independent, but temperature influenced the germination rate. Constant 25°C promoted higher total germination (86%), fewer days (8.3) to germinate, and a shorter span of days (4.3) than other constant temperatures or alternating temperatures of 25°–30°, 20°–30°, 15°–25°, 25°–35°, or 15°–35°. Exposures to 10° or 40° for 1 to 3 days during various seed germination phases reduced germination by 14% to 23% and delayed radicle emergence, but 40° for 1 to 3 days caused larger reductions in germination than comparable durations at 10°. Exposure of seeds to 10° or 40° between days 2 and 4 caused the largest reductions in total germination.
Abstract
Seeds of Hippeastrum × hybridum Hort. were subjected to dehydration, freezing, and storage for 12 months at various temperature and humidity levels. Amaryllis seed viability was unaffected by dehydration that removed 97% of available moisture content at seed harvest. Seeds were tolerant of freezing, but germination was reduced gradually as freezing temperatures decreased from 0° to −80°C. Moisture content at freezing influenced loss of viability; the lower the moisture content the higher the germination percentages. Temperature and relative humidity during seed storage governed seed viability loss rate. No measurable losses in viability resulted from storing seeds at 11% or 52% RH at 5° or 15°, respectively, for 12 months, but viability was significantly decreased when seeds were stored at these humidities at 25° or 35°. Viability decreased substantially or was lost after 3 months of storage at 75% and 95% RH and 25° and 35°.
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.
High synchrony, rate, and germination of needle palm [Rhapidophyllum hystrix (Pursh) H.A. Wendle & Drude] seeds were achieved only after removing the sclerotesta and embryo cap, which imposed physical dormancy. After scarification, recently harvested seeds or seeds stored for 12 months at 5C and 100% relative humidity had 96% and 98% final germination (G), with 9 to 11 days required to achieve 50% of final germination (T50) at 30C. Germination temperature controlled G, T50, and days between 10% and 90% of final germination (T90 - T10) of scarified seeds, with respective values of 98%) 9 days, and 5 days at 30C, and 18%, 31 days, and 12 days at 15C. Seeds with 36% moisture at harvest had no reduction in G until moisture was <14%. Germination of seeds with 19% moisture declined from 80% if stored at 0C to 33% if stored at -l0C; no seeds germinated after storage at less than -l0C.
The role of light on impatiens seed germination and radicle emergence was studied. Seeds having a photodormancy require light for only part of the germination period. Germination ≥85% was achieved after 3, 2, or 1 day of irradiance at 1.5, 15, or 75 μmol·s-1·m-2, respectively. Keeping imbibed seeds in darkness for ≥2 days before light exposure caused reduced total germination percentages (G), delayed achieving 50% of the final germination percentage (T50), and increased the days between 10% and 90% germination (T90-T10). Light for 6 hours daily at 1.5, 15, or 150 μmol·s-1·m-2 promoted high G and rapid and uniform germination, but daily 12 to 24 hours of irradiance decreased G and increased T50 and T90-T10. Estimated rates of decline (increase) in G, T50, or T90-T10 with each added day of light (darkness) or increasing daily hours of light were measured by fitting regression equations. Impatiens seed germination was promoted by the initial 1 to 3 days of light, but light inhibited radicle extension in the latter germination stages.
Begonia ×semperflorens-cultorum Hort. `Prelude Scarlet' seeds varied within irradiance treatments in the irradiance level and duration that they required to reach the light saturation value and germinate. At high photosynthetically active radiation (PAR), seeds required light for only part of the germination period to terminate photodormancy. Germination >90% was achieved after 4 and 1 day of 24 hours/day exposure to PAR at 15 and 150 μmol·m–2·s–1, respectively, but 82% germination occurred after 4 days of irradiance at 1.5 μmol·m–2·s–1 at 27C. Fewer days to 50% of final germination (T50) and between 10% and 90% germination (T90 – T10) were required when light saturation was achieved after 1 day at high PAR rather than after 4 days at a low PAR level. The total PAR that seeds received during 6, 12, or 24 hours of light daily determined the total percentage of the seeds that germinated. Seeds receiving 150 μmol·m–2·s–1 continuously for ≥24 hours achieved 90% germination, but 6 or 12 hours daily at this irradiance level required 4 days and 3 days, respectively. Trends in total germination percentages (G), T50, or T90 – T10 with increased PAR levels, hours of light daily, or days of light were found by fitted regression equations and Tukey's hsd procedure. Begonia seed germination was promoted by PAR levels of 1.5 to 150 μmol·m–2·s–1 for periods ≤4 days, with darkness thereafter until cotyledon emergence.
Temperature, relative humidity (RH), desiccation, and hydration affect gerbera (Gerbera jamesonii H Bolus ex Hook.f.) seed storage and germination. Germination percentages (G) were maximal and about equal at constant 15, 20, or 25C in darkness or light but lower at alternating temperatures having the same mean temperature. The number of days to 50% final germination (T50) and between 10% and 90% germination (T90 – T10) required the fewest days at constant 25 or 30C; longer germination periods resulted with alternating temperatures. Reducing seed moisture from 7.1% to 3.5% had no effect on G, T50, or T90 – T10 values, but at seed moisture levels <3.5%, G was lower and T50 and T90 – T10 longer. Germination percentages were similar after seed storage from 5 to –5C, but G was lower after storage at –10C or lower. Low-temperature seed storage had no effect on T50 or T90 – T10 values. Seeds had highest G and lowest T50 and T90 – T10 values when germinated at 52% seed moisture, with large declines and delays in germination at lower and higher moisture levels. Seed storage for 12 months without reduction in germination was possible at 5C and 11% or 32% RH. Seeds stored at 52% RH lost G at all temperatures, and no seed germinated after storage at 75% RH and 15 or 25C. Seed stored at 5 or 15C and 11% to 32% RH had the fewest days to T50 and T90 – T10.
Various combinations of temperature and moisture contents were used in evaluating the seed storage of nine genera of annual flowers. Relative humidity (RH) levels of 11%, 32%, 52%, and 75% provided wide ranges in seed moisture during storage at 5, 15, and 25C. At each temperature, total germination percentages (G) generally declined as seed moisture content increased during storage. The seed moisture range giving the highest G after 12 months of storage was determined for each temperature and plant genus. For all genera, seed moisture contents during storage increased as storage temperatures increased at constant RH levels. Moisture contents at 25C storage were 37%, 34%, 29%, and 20% higher than at 5C when RH levels were at 11%, 32%, 52%, and 75%, respectively.