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  • Author or Editor: J.A. Cornell x
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The interactions among IBA concentrations and durations of treatment and propagation medium temperatures on the rooting of stem cuttings were compared for cultivars of Hibiscus rosa-sinensk L. Cultivar rooting was rapid with extensive root development for `Pink Versicolor', average for `Jim Hendry', and slow with few roots per cutting for `Silver Anniversary'. The IBA concentration and duration of treatment that cuttings required to reach maximum rooting declined with increase in medium temperature (from 18 to 34C). `Pink Versicolor' stem cuttings receiving 4- to 6-minute basal dips required 8000 ppm IBA with the medium at 18C, 6000 ppm at 26C, and 2500 ppm at 34C, to achieve 100% rooting of the cuttings. `Pink Versicolor' stem cuttings had the most roots at 10,000 ppm IBA, with 10-min stem dips best at 18C, 4 to 8 min at 26C, and 7 to 8 min at 34C. Maximum dry weights per root were achieved at 6000 ppm IBA, with longer basal stem dip durations needed at 18C than 26 or 34C. Lower IBA levels were required for 100% rooting of `Pink Versicolor' than for `Jim Hendry', with highest levels needed for `Silver Anniversary'. The results indicated that the benefits in rooting achieved from higher IBA levels greatly exceeded those that could be achieved by increased medium temperature. Chemical name used: indole-3-butyric acid (IBA).

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Gladiolus (G. grandiflorus) seed germination was light-independent, but temperature influenced the germination rate. Constant 20C promoted higher total germination (97%), fewer days (4.3) to 50% of final germination, and shorter span of days (4.8) between 10% and 90% germination than other constant temperatures, although similar results were achieved by alternating 12-h cycles of 20 to 25C. Total germination was unchanged after seed treatment for 7 days at 10 to -20C, but longer germination periods were required after treatments below -10C. Reducing seed moisture contents from 11.8% to 4.2% caused no reduction in total germination, but moisture contents below 6.6% delayed achieving 50% of final germination and extended the periods from 10% to 90% of germination. Temperature and relative humidity (RH) during storage were important in retaining seed viability, with RH having a larger effect. Smallest declines in total germination during 12 months of storage occurred at 11% and 33% RH at 15C. The statistical analysis estimated the optimum seed storage at 14C and 26% RH.

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Planting treatments were evaluated for their influence on shoot development and root distribution of own-rooted `Redhaven' peach [Prunus persica (L.) Batsch] trees planted to high density (5000 trees/ha). Planting in fabric-lined trenches (FLT) or narrow herbicide strips (NHS) reduced the diameter and length of primary shoots, the number and combined length of second-order shoots, and the total length of shoots. Flower density, the number of flowers per node, and the percentage of nodes containing one or more flowers were increased for FLT trees but not for NHS trees when compared with controls. The length of primary shoots increased quadratically for all treatments with increasing limb cross-sectional area (LCA). The total length of shoots increased more with increasing LCA for controls than for FLT trees. The number of flowers per shoot increased linearly for all treatments with increasing LCA values. Root concentration decreased with increasing soil depth and distance from tree rows for all treatments. Reduced widths of weed-free herbicide strips had little effect on root distribution. Roots of FLT trees were reduced in number and restricted vertically and laterally when compared with other planting treatments. The FLT treatment modified shoot development by reducing the length of total shoots and length of primary shoots across LCA values measured when compared with NHS and control-treatments.

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Phlox drummondii Hook seed germinated well over a wide range of constant or alternating temperatures. Germination percentages at constant temperatures of 10 to 25C ranged from 94% to 98% for `Light Salmon' and from 83% to 88% for `Deep Salmon'. No seeds germinated at constant 30C. Total germination percentages at alternating temperatures ranged from 93% to 99% for `Light Salmon' and 67% to 82% for `Deep Salmon'. For both cultivars, the number of days to 50% of final germination (T50) and between 10% and 90% germination (T90-T10) decreased as constant temperatures or the median for alternating temperatures rose from 10 to 20C. The seeds had only limited desiccation tolerance. Reducing the moisture content of stored seed from 9 % to 5 % did not reduce total germination significantly, but 5% to 6% seed moisture levels increased the days to T50 and T90-T10 compared with higher moisture contents. The relative humidity and temperature that phlox seed received during long-term storage influenced germination. After seed was stored at 5C, germination generally was higher, earlier, and more uniform than after storage at 15 or 25C. The highest total germination percentages and shortest T50 and T90-T10 occurred following storage for 12 months at 5C and 20% to 40% relative humidity.

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Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] was grown at two sites differing slightly in Mehlich-I (double-acid) -extractable P (6 and 10 mg·kg-l soil). Early and total yields responded positively to P rate; however, maximum yields were obtained with small amounts of P fertilizer. The linear-plateau critical P fertilizer rates were 26 and 27 kg·ha-1 at sites 1 and 2, respectively. These critical rates were lower than those currently used for recommending P fertilizer on soils that have very low P. Phosphorus concentrations of most-recently matured leaves at early fruit set were 2.5 and 2.8 g·kg-1 at sites 1 and 2, respectively, with 0 P, and 4.4 and 4.8 g·kg-1 with the 25-kg P/ha treatment.

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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.

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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.

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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.

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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.

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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.

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