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Robert J. Dufault and Jonathan R. Schultheis

To reduce transplant shock of bell peppers (Capsicum annuum L.), we tested the effectiveness of pretransplant nutritional conditioning (PNC) as a promoter of earliness and yield. In Expt. 1, `Gatorbelle' bell pepper seedlings were fertilized with N from Ca(NO3)2 at 25, 75, or 225 mg·liter-1 and P from Ca(H2PO4)2 at 5, 15, or 45 mg·liter-1. Nitrogen interacted with P, affecting shoot fresh and dry weight, leaf area, root dry weight, seedling height, and leaf count. In Expt. 2, transplants conditioned with N from 50, 100, and 200 mg·liter-1 and P at 15, 30, and 60 mg·liter-1 were field-planted in Charleston, S.C., and Clinton, N.C. Nitrogen- and P-PNC did not greatly affect recovery from transplant shock. Although N- and P-PNC affected seedling growth in the greenhouse, earliness, total yield, and quality were similar in field studies among all PNC treatments at both locations. PNC with 50 mg N and 15 mg P/liter can be used with this variety and not have any long-term detrimental effects on yield and quality.

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Robert J. Dufault and Regina R. Melton

Tomato seedlings (Lycopersicon esculentum Mill. `Sunny') were exposed to cyclic cold stress at 2 ± 1C, then to 29 ± 6C in a greenhouse before being transplanted to the field. Cold-stressed seedlings were transplanted when the risk of ambient cold stress was negligible. In the first year of a 2-year study, transplants were exposed to 2C for 3, 6, or 12 hours for 1, 3, or 6 days before field planting. In the second year, transplants were exposed to 2C for 6, 12, or 18 hours for 4, 7, or 10 days before field planting. In the first year, cold stress generally stimulated increases in seedling height, leaf area, and shoot and root dry weights but decreased chlorophyll content. In the second year, all seedling growth characteristics except leaf area and plant height were diminished in response to longer cold-stress treatment. In both years, earliness, total productivity, and quality were unaffected by any stress treatment. Therefore, cold stress occurring before transplanting has a negligible effect on earliness, yield, or quality.

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Regina R. Melton and Robert J. Dufault

`Sunny' tomato (Lycopersicon esculentum Mill.) seedlings were pretransplant nutritionally conditioned (PNC) in 1988 and 1989 with factorial combinations of N from 100 to 300 mg·liter-1 and P from 10 to 70 mg·liter-1. In 1988, all conditioned seedlings were exposed to 12 hours of 2C for eight consecutive nights before transplanting. In 1989, half of the conditioned plants were exposed to a low-temperature treatment of 8 days with 12-hour nights at 2C and 12-hour days in a warm greenhouse (19C/26C, night/day). In both years, as N PNC increased to 200 mg·liter-1, seedling growth increased. Increasing P PNC from 10 to 40 mg·liter-1 increased seedling growth, but only in 1988. In both years, P PNC did not affect yields. Low-temperature exposure in 1989 decreased seedling growth in comparison to those held in a warm greenhouse (19C/26C, day/night). In 1988, first harvest yields were not affected by N PNC; however, in 1989, as N increased to 200 mg·liter-1, early yields increased. In 1988, total yields increased wit h N PNC from 100 to 200 mg·liter-1 and in 1989 with N at 50 to 100 mg·liter-1 with no further increases from 100 to 200 mg·liter-1. Low-temperature exposure had no effect on earliness, yield, or quality. A PNC regime combining at least 200 mg N/liter and up to 10 mg P/liter should be used to nutritionally condition `Sunny' tomato seedlings to enhance yield.

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Regina R. Melton and Robert J. Dufault

Tomato (L.ycopersicon esculentum Mill.) seedlings were nutritionally conditioned with solutions containing factorial combinations of N at 25, 75, and 225 mg·liter -1, P at 5, 15, and 45 mg·liter-1, and K at 25, 75, and 225 mg·liter -1 to determine the effect of nutritional regimes on tomato transplant growth and quality. As N increased from 25 to 225 mg·liter-1, fresh shoot weight, plant height, stem diameter, leaf number, leaf area, shoot and root dry weights, and total chlorophyll increased. Nitrogen accounted for the major source of variation. Phosphorus effects were significant only in 1988; Pat 45 mg·liter-1 increased fresh shoot weight, plant height, stem diameter, leaf number, and leaf area in comparison to 5 and 15 mg·liter -1. Potassium did not significantly influence any of the growth variables measured in the study. For quality transplant production, nutrient solutions should contain at least N at 225 mg·liter-1, P at 45 mg·liter-1, and K at 25 mg·liter-1.

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Jonathan R. Schultheis and Robert J. Dufault

Pretransplant nutritional conditioning (PNC) of transplants during greenhouse production may improve recovery from transplanting stress and enhance earliness and yield of watermelon [Citrullus lanatus (Thumb.) Matsum. & Nakai]. Two greenhouse experiments (Expts. 1 and 2) and field experiments in South Carolina and North Carolina (Expt. 3) were conducted to evaluate N and P PNC effects on watermelon seedling growth and their effects on fruit yield and quality. `Queen of Hearts' triploid and `Crimson Sweet' diploid watermelon seedlings were fertilized with N from calcium nitrate at 25, 75, or 225 mg·liter–1 and P from calcium phosphate at 5, 15, or 45 mg·liter–1. In the greenhouse, most variation in the shoot fresh and dry weights, leaf count, leaf area, transplant height, and root dry weight in `Queen of Hearts' and `Crimson Sweet' was attributed to N. Cultivar interacted with N, affecting all seedling growth variables, but not leaf area in Expt. 2. To a lesser extent, in Expt. 1, but not in Expt. 2, P interacted with cultivar, N, or cultivar × N and affected shoot fresh and dry weights, leaf count and leaf area. In the field, transplant shock increased linearly with N, regardless of cultivar or field location. The effect of PNC on plant growth diminished as the growing season progressed. For both cultivars at both locations, N and P PNC did not affect time to first staminate flower, fruit set, fruit width or length, soluble solids concentration, or yield. Vining at Charleston for both cultivars was 2 days earlier when N was at 75 rather than 25 mg·liter–1, without further change with the high N rate. At Clinton, the first pistillate flower was delayed linearly the higher the N rate for `Crimson Sweet'. At Charleston, hollow heart in the `Queen of Hearts' increased nearly 3 times when N PNC rate was tripled (from 75 or 225 mg·liter–1), while N had no effect on hollow heart in `Crimson Sweet'. In contrast, at Clinton, hollow heart in either cultivar was affected by P PNC, not N. PNC with 25N–5P (in mg·liter–1) can be used to reduce seedling growth and produce a more compact plant for easier handling, yet not reduce fruit quality or yield.

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Richard L. Hassell, Robert J. Dufault, and Tyron L. Phillips

Early spring sweet corn (Zea mays var. rugosa) is usually planted in cold soils at sub-optimal temperatures for seed germination. It is important for growers to understand the relationships among temperature, germination, and vigor of sweet corn in order to plan the earliest planting dates that will not significantly reduce plant stand. The objectives of this research were 1) to determine the minimum temperatures to germinate to 75%, (the minimum germination percent for interstate commerce) for 27 new sweet corn su (sugary), se (sugar enhancer), and sh2 (shrunken-2) cultivars; 2) to determine vigor differences among the phenotypes; and 3) to select the most promising se, su, and sh2 cultivars for cold tolerance and vigor for early spring planting. Seeds of each cultivar were placed along a temperature gradient on a thermogradient table, Type 5001 (Seed Processing Holland, Enkhuizen, The Netherlands), and allowed to germinate over a 7-day period. The gradient treatments were [±2 °F (1.1 °C)] 52, 56, 60, 64, 68, 72, 76, 80, 84, and 86 °F (11.1, 13.3, 15.6, 17.8, 20.0, 22.2, 24.4, 26.7, 28.9, and 30.0 °C). Germination data from thermogradient testing were used to determine the minimum temperatures and time required for su, se, and sh2 cultivars to germinate at ≥75%, defined as minimum acceptable germination percent (MAGP); and the minimum temperature to reach the maximum germination rate (MGR) for a cultivar, defined as the ability to germinate to MAGP at the same rate equally at low and high temperatures. Generally, su phenotypes germinated to MAGP within 4 days, with sh2 requiring 6 days, but with se requiring 5 days. We found that within each phenotype, however, cultivars reacted uniquely to temperature. The most vigorous and cold tolerant su cultivars were `NK 199' and `Merit' which germinated to MAGP at 52 °F with `NK 199' more vigorous than `Merit'. The su cultivar `Sweet G-90' was vigorous at warm temperatures, but the least cold tolerant and desirable for planting under cold conditions. Within the se cultivars, `Precious Gem', `July Gold', and `Imaculata' germinated to MAGP at 52 °F with `Precious Gem' requiring 6 days and `July Gold' and `Imaculata' requiring 7 days. `Accord' was the least cold tolerant se cultivar, requiring at least 60 °F for MAGP with a slow MGR, even at warm temperatures. None of the sh2 cultivars reached MAGP within 7 d at 52 °F, as was also observed for certain su and se cultivars.

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Robert J. Dufault, Tyron L. Phillip, and John W. Kelly

Gerbera seedlings (Gerbera jamesonii H. Bolus Ex. Hook F.) `Florist Strain Yellow' were planted on drip-irrigated, plastic-mulched beds at 24,000, 36,000 or 72,000 plants/ha. Nitrogen and potassium fertilizers at 55, 110, or 220 kg·ha-1 were factorially combined with populations. In the 1st year of a 2-year study, the number of marketable flowers increased as N and K increased to 110 kg·ha-1, but as N and K were increased to 220 kg·ha-1, cull production increased. In the 2nd year, marketable and cull yields increased with N rate to 220 kg·ha-1; K did not affect yield. As populations increased from 24,000 to 72,000 plants/ha, marketable and cull flower production increased in both years. Flower size and quality were unaffected by plant populations. Nitrogen and potassium fertility did not affect flower size, quality, or vase life in either year.

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Robert J. Dufault, Brian Ward, and Richard L. Hassell

The objective of this study was to determine the best combination of planting dates (PDs) and cultivars on yield and quality for long-term production of romaine lettuce. `Green Forest' (GF), `Apache' (AP), `Darkland' (DK), `Green Tower' (GT), `Ideal Cos' (IC), and `Tall Guzmaine' (TG) were successfully grown to harvest maturity on 19 PDs from September 1998 to April 2001. Lettuce planted in September and April PDs (pooled over cultivars and year), required as little as 47 and 49 days, respectively, to reach harvest (all cultivars harvested on the same day). Lettuce planted in October, November, February, and March PDs (pooled over cultivars and year), required on average 64, 66, 75, and 67 days to reach harvest, respectively, but in the coldest PDs of December and January, 90 and 98 days, respectively, were needed to reach maturity. Of the eight PDs evaluated, marketable numbers/plot (pooled over cultivars and years) were greatest in the September PD, followed by April (–8% decrease from September PD) > March (–13%) > October (–17%) > November (–21%) > December = January = February (about –30%) and heads weighed the most in September > January = February (–7% decrease from September PD) > March = April (–14%) > October (–21%) > December (–25%) > November (–31%). Cull heads/plot (pooled over cultivars and years) were greatest in April > December (–5% decrease from April PD) > January = February (–16%) > November (–27%) > October (–34%) > March (–44%) > September (–49%). Two out of three November PDs were lost to freezing damage and this PD should be avoided. Significant bolting occurred primarily in the September and October PDs (in 1 of 3 years) with negligible bolting in the November, December, and January PDs, but bolting recurred again in the February, March and April PDs. Marketable numbers/plot (pooled over all PDs and years) were greatest for GF > GT (–7% decrease from GF) > AP (–8%) > IC (–9%) > DK (–11%) > TG (–21%). The interaction effect of cultivar × PD indicated that GF yielded the most marketable heads in 6 out of 8 PDs. The best performing cultivars by PD (pooled over years) were September and February = GF and IC; October = TG; November = AP; December, January, March, and April = GF.

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Richard L. Hassell, Robert J. Dufault, and Tyron L. Phillips

Ten triploid and 25 diploid watermelon (Citrullus lanatus) selections were evaluated to determine the temperature range and length of test for which germination index (rate of germination over time) and germination percentages were maximum for expediting vigor and seed testing practices. Temperature interacted with watermelon selection indicating that certain selections germinated faster within specific, but differing temperature ranges. Within 2 days after starting the germination process, 90% of triploid selections and 96% of diploid selections germinated to their greatest level and prolonging germination data collection for one week did not change this relationship. Although optimal temperature ranges may differ among the selections, the one temperature within the range common for all selections evaluated that maximized germination was 85 to 90 °F (29.4 to 32.2 °C) for diploids and 85 °F for triploids.

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Robert J. Dufault, Ahmet Korkmaz, Brian K. Ward, and Richard L. Hassell

Extending the production season of melons (Cucumis melo L.) by using very early and late planting dates outside the range that is commercially recommended will increase the likelihood of developing a stronger melon industry in South Carolina. The objective of this study was to determine if early (February) transplanted melons or later (June through July) planting dates are effective in extending the production season of acceptable yields with good internal quality of the melon cultivars: Athena, Eclipse, and Sugar Bowl and Tesoro Dulce (a honeydew melon). Melons were transplanted in Charleston, S.C., in 1998, 1999, and 2000 on 12 and 26 Feb., 12 and 26 Mar., 9 and 23 Apr., 7 and 21 May, 4 and 18 June, and 2 July and required 130, 113, 105, 88, 79, 70, 64, 60, 60, 59, and 56 days from field transplanting to reach mean melon harvest date, respectively. Stands were reduced 67%, 41%, and 22% in the 12 and 26 Feb. and 12 Mar. planting dates, respectively, in contrast to the 26 Mar. planting date but ≤15% in all other planting dates. Planting in February had no earliness advantage because the 12 and 26 Feb. and 12 and 26 Mar. planting dates, all reached mean melon harvest from 19 to 23 June. Comparing the marketable number of melons produced per plot (averaged over cultivar) of the standard planting dates of 12 and 26 Mar. indicated decreases of 21%, 32%, 36%, 36%, 57%, 57%, and 54%, respectively with the planting dates of 9 and 23 Apr., 7 and 21 May, 4 and 18 June, and 2 July. The most productive cultivar of all was `Eclipse', which yielded significantly more melons per plot in all 11 planting dates followed by `Athena' (in 8 of 11 planting dates), `Tesoro Dulce' (7 of 11 planting dates), and `Sugar Bowl' (2 of 11 planting dates). In our study, any planting date with melon quality less than the USDA standard of “good internal quality” or better (Brix ≥9.0) was considered unacceptable because of potential market rejection. Therefore, the earliest recommended planting date with acceptable yield and “good internal quality” was 12 Mar. for all cultivars; the latest planting dates for `Athena', `Eclipse', `Tesoro Dulce', and `Sugar Bowl' were 4 June, 18 June, 7 May, and 9 Apr., respectively. With these recommendations, the harvest season of melons lasted 40 days from 24 June to 3 Aug. for these four cultivars, which extended the production season an additional 2 weeks longer than the harvest date of last recommended 21 May planting date.