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Stefania De Pascale, Albino Maggio, Celestino Ruggiero, and Giancarlo Barbieri

We irrigated field-grown celery (Apium graveolens L. var. dulce [Mill.] Pers. 'Tall Utah') with four concentrations of saline water, NSC (nonstressed control), SW1, SW2, and SW3, corresponding to EC of 0.5, 4.4, 8.5, and 15.7 dS·m-1, respectively, plus a nonirrigated control (NIC) and investigated the effects of the treatments on water relations, yield and ion content. In addition, we compared simultaneously plant response to both salt and drought stress by using a modified version of the threshold-slope model. Increasing salinity of the irrigation water reduced fresh and dry weights of the shoots, but increased the dry matter percentage in shoots. The marketable yield was moderately affected by salinity (25% reduction at EC 8.5 dS·m-1). In contrast, a severe water stress dramatically decreased the marketable yield from 23 t·ha-1 (average of the irrigated treatments) to <7 t·ha-1 (nonirrigated control). Na+ and Cl- concentrations increased in salinized plants whereas nitrogen content, K+, Ca2+, and Mg2+ concentrations decreased upon salinization. Midday leaf water potentials (Ψt) decreased from -1.48 MPa (0.5 dS·m-1) to -2.05 MPa (15.7 dS·m-1) and - 2.17 MPa (nonirrigated control), though the reduction in leaf cellular turgor was less severe. The maintenance of high leaf cellular turgor was positively correlated to a decrease in osmotic potential and to an increased bulk modulus of elasticity. These results indicate that it is possible to irrigate celery with saline water (up to 8.5 dS·m-1) with acceptable losses in marketable yield and confirmed that in the field, this species has the ability to efficiently regulate water and ion homeostasis. In the absence of irrigation, celery plants were unable to cope with the drought stress experienced, although this was comparable, in terms of soil water potential, to the one caused by saline irrigation.

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Mary E. Mangrich and Mikal E. Saltveit Jr.

Ethylene induces arenchyma formation in corn roots and other plant tissues, and abscisic acid (ABA) induces arenchyma in celery petioles. Pithiness (i.e., arenchyma) in celery can be measured as a decrease in density. Density was calculated for two cm long petiole segments by dividing their weight by their volume as calculated from the weight of water displaced upon immersion. The relationship between density (g/ml) and subjective pithiness rating (1 = none, 9 = severe) was linear (r2 = 0.87). Petiole segments exposed to 0 to 200 ppm ethylene in air at 5C for two weeks did not exhibit any significant differences (p = 0.05) in density among the treatments. Entire petioles were treated with 0, 1, 10, and 100 μM ABA in water for 96 h at 25C. The petioles were cut into thirds and the center 2 cm from each portion was excised and the density measured. Although density decreased in the top to the bottom portions over all ABA conc, the differences were not significant. Density was significantly reduced in segments excised from the bottom and middle of petioles treated with 10 and 100 μM ABA, compared to 0 and 1 μM ABA. There also was a decrease in density with ABA conc in the top portion, but the decrease was only significant for the 100 μM ABA conc.

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Kevin Charles*, Mathieu Ngouajio, and Darryl Warncke

Cover crops are commonly used to improve soil fertility and enhance crop performance. Field experiments were conducted to determine the effects of different cover crops and fertilizer rates on celery growth and development. The experiment was a two-way factorial with a split plot arrangement. The main plot factor was cover crop and included cereal rye (Secale cereale), hairy vetch (Vicia villosa), oilseed radish [Raphanus sativus (L.) var. oleiferus Metzg (Stokes)], and no cover crop. The sub-plot factor was fertilizer rate with three levels: full (160, 80, 400), half (80, 40, 200), and low (80, 0, 0) kg/ha of N, P2 O5, K2 O, respectively. The cover crops were grown during Fall 2002 and incorporated prior to celery transplanting in May 2003. During celery growing season, stalk length, above and below ground biomass were assessed at 23, 43, 64, and 84 days after planting (DAP). The biomass produced by oilseed radish (719 g/m2) exceeded that of cereal rye (284 g/m2) and hairy vetch (181 g/m2). At 23 and 43 DAP, celery fresh root (4.8 and 11.4 g/root) and shoot (6.1 and 53.6 g/shoot) biomass of oilseed radish exceeded the values of all other cover crops. At 84 DAP however, celery shoot fresh weight was similar in all cover crop treatments. Celery plants were tallest in the cereal oilseed radish and rye treatments early in the season; however final plant height at harvest was not affected by type of cover crop. The amount of fertilizer applied had a significant effect on celery growth starting at 64 DAP and continued until harvest. These results suggest that the large biomass produced by oilseed radish played an important role in early season celery growth.

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Yehoshua Saranga, David Rhodes, and Jules Janick

Tolerance to partial desiccation and amino acid composition of celery (Apium graveolens L. cv. SB 12) somatic embryos were investigated under various culture durations and with exogenous application of 1 μm ABA, proline, and/or γ -aminobutyrate (GABA). ABA consistently increased tolerance to partial desiccation and elevated proline and GABA content of embryos. The changes in tolerance to partial desiccation associated with changes in culture duration (optimum 9 to 10 days) correlated with embryo proline content. Exogenous proline increased embryo proline content and tolerance to partial desiccation. Exogenous GABA increased embryo GABA content and tolerance to partial desiccation only when applied in combination with proline. Chemical name used: abscisic acid (ABA).

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Carlos A. Parera, Ping Qiao, and Daniel J. Cantliffe

To alleviate high-temperature-induced reductions in seed germination, emergence, and seedling uniformity in celery (Apium graveolens L.), seeds were primed via solid matrix priming (SMP); 0.5 g celery seeds was incubated at 15C with 10 g calcined clay and 2 ml water. After 2 days, 1, 2, 3, or 4 ml water or 1% NaOCl solution was added and seeds were kept for 2, 4, 6, 8, 10, 12, and 14 additional days. The germination percentage and coefficient of germination velocity (COV) were calculated for each treatment at 15 and 30C. The seeds primed with NaOCl gained significantly less moisture after 8 days of priming than those treated with water, regardless of the volume added. Germination of nonprimed seeds was 83% and 2% at 15 and 30C, respectively. Final germination at 30C increased to >80% when seeds were primed with 3 or 4 ml NaOCl solution or 3 ml water for >10 days. SMP treatment significantly reduced the negative effect of high temperature on celery seed germination.

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L. Espinoza, C.A. Sanchez, and T.J. Schueneman

Four field experiments were conducted during two production seasons to evaluate soil-test P fertilizer recommendations for celery (Apium graveolens var. dulce) produced on Histosols, which often are linked hydrologically to environmentally sensitive wetlands, and to evaluate band placement as a strategy for improving P fertilizer-use efficiency in celery in such areas. Phosphorus was applied (broadcast or banded) at 0,50, 100,150, and 200 kg P/ha. Broadcast P was surface-applied and disked into the soil ≈ 15 cm deep 1 day before planting. Banded P was applied 5 cm below the soil surface and 5 cm to the side of each celery row. Total above-ground mass, marketable trimmed yield of celery, and yield of the larger grade sizes increased with P rate in all experiments. Band P placement was not a viable strategy for improving P fertilizer-use efficiency for celery. However, our results indicate that previous soil-test-based P fertilizer recommendations for celery were too high for the cultivars grown currently, and improved P fertilizer-use efficiency can be obtained with revised soil-test calibrations.

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S.J. Breschini and T.K. Hartz

Trials in nine commercial celery (Apium graveolens L.) fields were conducted between 1997-99 to evaluate grower drip irrigation management practices and their effects on yield and quality. Surface drip irrigation tapes with flow rates higher and lower than the grower-installed tapes were spliced into the field system; as the cooperating growers irrigated and applied N fertigation according to their routine practices these drip tapes delivered either more or less water and N than the field drip system. Total grower water application during the drip-irrigated portion of the season ranged from 85% to 414% of seasonal reference evapotranspiration (ETo). Water volume per irrigation varied among fields from 1.8 to 3.8 cm, with irrigation frequency varying from an average of every other day to once a week. Grower management of drip irrigation was not consistently successful in maintaining soil water tension (SWT) in a desirable range. SWT was often below -30 kPa, and in some cases below -70 kPa. These transient stresses were more often a result of inappropriate irrigation frequency than applied water volume. In four of the fields plots receiving less water than that delivered by the field system produced equivalent marketable yield and quality, indicating a significant potential for water savings. An economically important incidence of petiole pithiness (collapse of parenchyma tissue) was observed in four fields. Infrequent irrigation under high ETo summer conditions, rather than irrigation volume applied, appeared to be the major factor in pith development. N fertigation amount and crop N status appeared to be unrelated to pithiness severity. We conclude that celery drip irrigation management could be substantially improved by maintaining a closer proportionality between irrigation and crop evapotranspiration (ETc), increasing irrigation frequency, and reducing volume per irrigation.

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Jeanine M. Davis and Wayne H. Loescher

Diurnal fluctuations in soluble carbohydrates and starch were monitored in young (expanding), mature (first fully expanded), and old (nearing senescence) celery (Apium graveolens L.) leaves. In all tissues, mannitol and sucrose were the carbohydrates present in the highest concentrations. In old and young leaflets and their petioles, there was little change in levels of mannitol and sucrose in 26 hours. In mature leaflets, sucrose accumulated in the light and decreased in the dark; mannitol increased slightly in late afternoon. Starch concentration, although quite low, showed definite diurnal fluctuations in mature leaflets, but only small changes in young and old leaflets. Both sucrose and mannitol were present in mature petiole phloem tissues. Mannitol concentrations were high in the adjacent storage parenchyma tissue, but sucrose was almost undetectable. These data support earlier findings that sucrose is produced, translocated, and metabolized throughout the celery plant. Mannitol is also translocated, but also serves as a major storage carbohydrate in leaf tissues, especially petiole parenchyma. Starch serves as a minor short-term storage compound in leaflets.

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Sylvie Jenni, Isabelle Gamache, John Christopher Côté, and Katrine A. Stewart

Growers of early stalk celery (Apium graveolens var. dulce) often experience financial losses due to bolting (the premature and rapid elongation of the main celery stem) in temperate regions. A method was developed to provide early warning of bolting in field-grown celery, on the basis of two criteria, one visual and one microscopic, for inflorescence development. Bolting could be detected 40 days after transplanting using the visual criterion, and as early as 30 days after transplanting using the microscopic criterion. Early detection of bolting using the visual and microscopic criteria provided celery growers with periods of, respectively, 25 days and up to 35 days to consider harvesting earlier, before the length of the celery stems exceeded commercial standards. This method could be effective in minimizing financial losses due to bolting when coupled with agro-economic studies.

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T.K. Hartz, W.E. Bendixen, and L. Wierdsma

The utility of presidedress soil nitrate testing (PSNT) in irrigated lettuce (Lactuca sativa L.) and celery (Apium graveolens L.) production was evaluated in 15 commercial fields in California from 1996 to 1997. Fields were selected in which soil NO3-N (5- to 30-cm depth) was >20 mg·kg–1 at the time the cooperating grower made the first sidedress N application. The grower's N regime was compared with reduced N treatments established by reducing or eliminating one or more sidedress applications. All fields were sprinkler and/or furrow irrigated, with minimal in-season precipitation. Reductions in seasonal N application averaging 143 and 209 kg·ha–1 N in lettuce and celery trials, respectively, had no effect on marketable yield in any field. Crop biomass N at harvest in the lowest N treatment in each field averaged 94% (lettuce) and 88% (celery) of that in plots receiving the full grower N program. Based on controlled-environment aerobic incubation of soil from 30 fields in long-term vegetable rotations, in-season N mineralization averaged 1% to 2% of soil organic N. A soil NO3-N “quick test” procedure utilizing a volumetric extraction of field-moist soil and measurement by nitrate-sensitive colorimetric test strips was evaluated and proved to be a practical on-farm method to estimate soil NO3-N concentration. Lettuce midrib NO3-N concentration at cupping stage was poorly correlated with current soil NO3-N level. We conclude that PSNT can reliably identify fields in which sidedress N application can be delayed or eliminated without affecting crop performance.