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

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

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

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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Charles S. Vavrina, Thomas A. Obreza, and John Cornell

`Tropical Quick' Chinese cabbage (Brassica rapa L., Pekinensis Group) was planted three times at 2-week intervals in Spring 1991 (direct-seeded) and two times in Fall 1991 (transplanted) in double rows on polyethylene-mulched beds to evaluate N source and rates. Calcium nitrate, ammonium nitrate, urea, urea-ammonium nitrate solution (Uran), and urea-calcium solution (Nitro-Pius) were applied preplant at 67,112, and 157 kg N/ha. The two later spring planting dates, compared with the earliest date, resulted in greater head fresh weights and higher insect damage incidence, but lower tipburn and flowering incidence. The earlier fall planting resulted in greater head fresh weight but a much higher flowering incidence than the later planting. Irrespective of planting date, head fresh weight increased quadratically, and tipburn and flowering incidence decreased linearly with increasing N rate. Although N source affected head fresh weight and tipbum incidence, differences were too small to be of practical value.

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George J. Hochmuth, Ed A. Hanlon, and John Cornell

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

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.

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

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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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.

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Luis A. Valdez-Aguilar, David William Reed, and John A. Cornell

The effect of Rb+ and Na+ as counter-cations of HCO3 was evaluated on bean (Phaseolus vulgaris L. cv. Poncho) plants using mixture experiment statistical methodology in a series of experiments set up in a controlled environment chamber. Mixture experiments using three components (Rb+, K+, and Na+) or two components (K+ and Na+) were conducted to delineate the toxicity of HCO3 versus the counter-cation effect. The quantitative separation of the toxic effects was possible only when the individual stress had an additive effect when combined with the other stress. Potassium mixtures were used as reference for comparison with other mixtures because plants did not respond to K+, probably because it was included at a minimum concentration of 2.5 mm K+ or because it was supplied in the preestablishing solution. Rubidium caused a decrease in shoot dry weight (SDW), but SDW accumulation was even lower when HCO3 was added to the Rb+ solutions. However, Rb+ was not included in follow-up experiments because the response of plants to Rb+ was very similar to that of Na+. The toxic effect of Na+ caused SDW to decrease at a rate of 3.7% per millimolar increase of Na+. However, the effect of HCO3 was dependent on its concentration, because at 2.5 mm HCO3 , the decrease in SDW was 12.7% per millimolar HCO3 , whereas at 3.75, 5, and 5.65 mm, the decrease was 11.0%, 7.8%, and 10.7% per millimolar HCO3 , respectively. At 7.5 mm HCO3 , the decrease in SDW was 4.2% to 8.2% per millimolar increase in HCO3 , respectively. The decreasing HCO3 rate may be explained by the nonadditive effect between HCO3 and Na+ at high alkalinity levels.

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George J. Hochmuth, Earl E. Albregts, Craig C. Chandler, John Cornell, and Jay Harrison

Strawberries (Fragaria ×ananassa Duch.) were grown in two seasons at Dover, Fla., with polyethylene mulch and drip irrigation. Nitrogen was injected weekly at 0.28 (50), 0.56 (100), 0.84 (150), 1.12 (200), and 1.40 (250) kg N/ha per day (kg·ha-1 for season) for `Oso Grande' and `Sweet Charlie' in 1991-92 season and for `Oso Grande' and `Seascape' in 1992-1993 season. Nitrogen fertilization in 1991-1992, over the range of 0.28 to 1.40 kg N/ha per day, had no significant effect on early (November to January) strawberry yields. March (the largest production month) yield and total-season yield increased with increasing N fertilization to 0.76 and 0.54 kg N/ha per day, respectively. Nitrogen fertilization did not affect yields of strawberry in 1992-93. Fruit firmness and average fruit weight were not affected by N fertilization from 0.28 to 1.40 kg N/ha per day. Nitrogen fertilization increased whole leaf N, leaf blade N, and petiole sap nitrate-N concentrations linearly for most sampling dates in both years. Early yields were greater for `Sweet Charlie' than `Oso Grande'. Yields were greater for `Oso Grande' during March, and total-season yields were similar for both cultivars in 1991-92. `Oso Grande' had greater early, March, and total yields than `Seascape' in 1992-93.