Onion Pungency Research Articles

Sulfur and nitrogen interaction affects onion yield and post-harvest quality

Ionic interactions affect the mineral composition of plants, which can cause nutritional disorders with reflections on yield, post-harvest quality, and food safety. Thus, this study evaluated the interaction between nitrogen (N) and sulfur (S) and its effects on onion production and post-harvest quality. The study was conducted in a completely randomized design, with a 3 × 5 factorial scheme and four replications. The treatments consisted of a combination of three S rates (0, 20, and 40 mg dm−3) and five N rates (0, 40, 60, 80, and 100 mg dm−3), applied in the form of calcium sulfate (CaSO4·2H2O) and urea, respectively. It was observed that the interaction between N and S negatively affected onion production, reducing the gain of both fresh and dry mass of the bulb. The N/S ratio ranged from 16.5 to 26.2 and was not influenced by the interaction between N and S. Onion pungency was classified as intermediate. The higher pungency value was obtained with the application of 100 mg dm−3 of N, and 40 mg dm−3 of S. The application of N when combined with 20 mg dm−3 of S contributed to increasing titratable acidity and soluble solids content of onion cv. Diamantina.

Gamma irradiation enhanced flavor volatiles and selected biochemicals in onion (Allium cepa L.) during storage

Gamma irradiation is recommended for inhibition of sprouting in onion during storage. The current study was aimed to understand the effect of gamma irradiation (100 and 200 Gy) on important parameters including flavor metabolites and phenolics of onion bulbs during ambient (26 ± 2 °C, 65 ± 2% RH) storage of 105 d. As analysed using GC/MS, 48 compounds were identified and quantified including aliphatic hydrocarbons, alcohols, esters, aldehydes, furans, and ketones. The organosulfur compounds were the prime odor volatiles (known for pungency) which increased (1.5 fold) in irradiated (200 Gy) onion during storage. The prominent phenolic acids (thirteen nos.) were quantified using GC/MS in onions during storage. Quercetin, the major phenolics in onion increased by more than 25 fold in irradiated and stored onion. The findings showed prominent enhancement of pungency in irradiated onion during storage. The content of pyruvic, ascorbic and phenolic acids including flavonoids and anthocyanins also increased during storage in onion bulbs. The ABTS and DPPH free radical scavenging activity increased by 1.5 and 2 times in irradiated and stored onion, respectively. However, no perceptible change was observed in texture, color, and overall sensory quality of onion bulbs. Unlike major vegetables, current findings showed that most of the quality indicators have enhanced upon storage in onion, which have added advantages.

Recent Advances in Onion Genetic Improvement

Onions are one of the most important vegetable crops worldwide. However, their production faces many challenges. Genetic improvement is one mechanism to address those challenges. In this review, we discuss recent research pertaining to the diseases Fusarium basal rot and Iris yellow spot, the insect pest onion thrips, onion pungency, and dormancy. Recent research for screening onion bulbs for Fusarium basal rot resistance has resulted in improved screening techniques and germplasm exhibiting less disease when inoculated with the disease-causing pathogen. Improved screening methods have resulted in germplasm exhibiting fewer and less severe Iris yellow spot symptoms when onion thrips and conducive environmental conditions are present. Onion germplasm with less and differing compositions of epicuticular wax on their leaves have shown a nonpreference for thrips feeding and have the potential for developing thrips tolerant cultivars. Conventional breeding efforts and genetic manipulation of the genes producing alliinase and lachrymatory factor synthase has resulted in low pungency, tearless onions. In long-day onions, an annual generation time has been achieved by artificially breaking bulb dormancy early while ensuring proper vernalization has been completed. Genetic improvement of these and many other onion traits will continue and result in better production in the future.

Comparative Metabolomics Profiling of Polyphenols, Nutrients and Antioxidant Activities of Two Red Onion (Allium cepa L.) Cultivars.

Onion is among the most widely cultivated and consumed economic crops. Onions are an excellent dietary source of polyphenols and nutrients. However, onions phytonutrient compositions vary with cultivars and growing locations. Therefore, the present study involved the evaluation of polyphenol, nutritional composition (proteins, nitrogen, and minerals), sugars, pyruvate, antioxidant, and α-amylase inhibition activities of red onion cultivars, sweet Italian, and honeysuckle grown in California and Texas, respectively. The total flavonoid for honeysuckle and sweet Italian was 449 and 345 μg/g FW, respectively. The total anthocyanin for honeysuckle onion was 103 μg/g FW, while for sweet Italian onion was 86 μg/g FW. Cyanidin-3-(6”-malonoylglucoside) and cyanidin-3-(6”-malonoyl-laminaribioside) were the major components in both the cultivars. The pungency of red onions in honeysuckle ranged between 4.9 and 7.9 μmoL/mL, whereas in sweet Italian onion ranged from 8.3 to 10 μmoL/mL. The principal component analysis was applied to determine the most important variables that separate the cultivars of red onion. Overall results indicated that total flavonoids, total phenolic content, total anthocyanins, protein, and calories for honeysuckle onions were higher than the sweet Italian onions. These results could provide information about high quality and adding value to functional food due to the phytochemicals and nutritional composition of red onions.

Effects of leaf cutting on bulb weight and pungency of short-day onions after lifting the plants

Short-day onions (Allium cepa L.) grown in the southern regions of the United States are commonly undercut and then dried for a few days before the bulbs are clipped and harvested. We conducted a study to evaluate the effects of leaf cutting on bulb weight and pungency of short-day onions after plant lifting in ‘TG 1015Y’, ‘Legend’, and ‘Texas Early White’ cultivars. When about 50% of the leaf had collapsed, plants were lifted from the field and the leaf was either cut at the neck (cut) or left intact (uncut, control). The plants were laid out to dry for 0, 3, or 7 days in a greenhouse with natural ventilation and the pungency and weights of the bulbs and leaves (partially dried to approximate normal field curing or dry weight) were measured. In a bulb–leaf paired test, bulb pungency was retained at the initial level in the cut treatment, while it showed an increasing trend in the uncut treatment, resulting in a gain of ˜0.8 μmoles mL−1 after 7 days in ‘TG 1015Y’. However, leaf pungency in the uncut treatment had 2.5 and 4.8 μmoles mL−1 less than that of the cut treatment after 3 and 7 days, respectively. Among cultivars, bulb pungency generally showed that the cut treatment had lower pungency levels, with some variation in change patterns and magnitudes of difference by the cultivar. The mildest cultivar ‘Legend’ had no difference but the most pungent cultivar ‘TEW’ showed 1.0–1.3 μmoles mL−1 less pungency by the cut treatment. Bulb weight was not reduced by the cut treatment, while leaf dry weight was generally heavier in the three cultivars. We considered that the lower bulb pungency in onions from cut plants was attributed to the severance of translocation of flavor compounds from leaf to bulb. Therefore, leaf clipping at the time of lifting and subsequent field curing is beneficial for producing less pungent onions for some cultivars.

Variability in spectrophotometric pyruvate analyses for predicting onion pungency and nutraceutical value.

Onion pyruvate concentration is used as a predictor of flavor intensity and nutraceutical value. The protocol of Schwimmer and Weston (SW) (1961) is the most widespread methodology for estimating onion pyruvate. Anthon and Barret (AB) (2003) proposed modifications to this procedure. Here, we compared these spectrophotometry-based procedures for pyruvate analysis using a diverse collection of onion cultivars. The SW method always led to over-estimation of pyruvate levels in colored, but not in white onions, by up to 65%. Identification of light-absorbance interfering compounds was performed by spectrophotometry and HPLC analysis. Interference by quercetin and anthocyanins, jointly, accounted for more than 90% of the over-estimation of pyruvate. Pyruvate determinations according to AB significantly reduced absorbance interference from compounds other than pyruvate. This study provides evidence about the mechanistic basis underlying differences between the SW and AB methods for indirect assessment of onion flavor and nutraceutical value.

Effect of Foliar Application of Micronutrients on Antioxidants and Pungency in Onion

The aim of the present work was to study the effect of foliar application of micronutrients [Zinc: Zn1 (0%); Zn2 (0.5%); Zn3 (1.0%) and Boron: B1 (0%); B2 (0.25%); B3 (0.5%)] on the antioxidants and pungency of onion cv. “Sukhsagar” (Allium cepa L.). In this experiment, it was suggested that the highest contents of total and free phenol was obtained by the highest dose of Zn (1%) in combination with 0% B, and single dose of Zn (0.5%) in combination with 0% B respectively. The superoxide dismutase (SOD) activity was found to increase with respect to control following the highest dose of B (0.5%) alone. However, the peroxidase (POD) activity increased more with respect to control following the single dose of B (0.25%) rather than the double dose (0.5%). The highest Molybdate reducing antioxidant potential (MRAP) was observed in 0.5% Zn in combination with 0% B, whereas that of 2, 2-Diphenyl-β-picrylhydrazyl radical scavenging activity (DPPHRAC) was found in the interaction effect of the double doses of both Zn (1%) and B (0.5%), which also offered the lowest lipid peroxidation. The highest pyruvic acid development was observed by the interaction effect of 0% Zn and 0.25% B. Based on the average values of the biochemical parameters and the results of PCA, the treatment with Zn1B3 (0% of Zn in combination with double dose of 0.5% of B) was proved to be most promising with respect to antioxidant properties.

Production and characterization of tearless and non-pungent onion.

The onion lachrymatory factor (LF) is produced from trans-S-1-propenyl-L-cysteine sulfoxide (PRENCSO) through successive reactions catalyzed by alliinase (EC 4.4.1.4) and lachrymatory factor synthase (LFS), and is responsible for the tear inducing-property and the pungency of fresh onions. We developed tearless, non-pungent onions non-transgenically by irradiating seeds with neon-ion at 20 Gy. The bulbs obtained from the irradiated seeds and their offspring bulbs produced by selfing were screened by organoleptic assessment of tear-inducing property or HPLC analysis of LF production. After repeated screening and seed production by selfing, two tearless, non-pungent bulbs were identified in the third generation (M3) bulbs. Twenty M4 bulbs obtained from each of them showed no tear-inducing property or pungency when evaluated by 20 sensory panelists. The LF production levels in these bulbs were approximately 7.5-fold lower than those of the normal onion. The low LF production levels were due to reduction in alliinase activity, which was a result of low alliinase mRNA expression (less than 1% of that in the normal onion) and consequent low amounts of the alliinase protein. These tearless, non-pungent onions should be welcomed by all who tear while chopping onions and those who work in facilities where fresh onions are processed.

Quantitative Evaluation of the Pyruvic Acid Content in Onion Samples with a Fully Validated High-Performance Liquid Chromatography Method

Onion cultivars with low pungency have been increasing in popularity because they are more attractive for fresh, uncooked use. The pyruvic acid amount is commonly used as a measure of onion pungency. For the first time the validation of a reversed-phase high-performance liquid chromatography method for the quantitative analysis of pyruvic acid in onion extracts was carried out. The established chromatography method based on the use of a 50 mM phosphate buffer (pH 2.5) eluent system provided good precision (RSD% in the range of 1.25–1.29, in the long-period) and accuracy (recovery% in the range of 97.70–111.62, in the long-period) as well as appreciably low limit of detection and limit of quantitation values (11.03 and 33.41 ng/mL, respectively). The validated method proved successful in the analysis of the onion extract from Dorata di Parma cultivar after a preliminary solid-phase extraction step. A significant adherence with results from previous spectrophotometric determinations turned out.

Effect of drying, freezing and storage of dried and frozen onion (Allium cepa L.) on its pungency

The paper contains results of studies of drying and freezing effects, as well as storage of dried and frozen onion on its pungency. The effect of onion bulbs preparation on pungency was estimated as well. The pungency measurements were based on determination of pyruvate produced enzymatically by alliinase. Storage at 20°C of skinned onion decreases sligthly pungency, however three weeks storage at 0-2°C did not change it. Other results indicate that freezing at -25°C, and followed thawing led to large losses - reaching 75% of pungency found in the onion taken to the process. Storage of the frozen onion caused further decrease its pungency. Decrease of pungency during drying was depended on temperature of the process. Low drying temperature (40 and 50°C, 20 hours) caused only 15-20% decline of pungency. Higher temperature drying (60°C) resulted in 50% losses of onion pungency.

Impact of selective flame weeding on onion yield, pungency, flavonoid concentration, and weeds

Field experiments were conducted to evaluate the effects of multiple selective flame weeding treatments on onion (Allium cepa L.). Onions were flamed between one and six times over the course of the season with a high (72 kg propane ha−1) or low (45 kg propane ha−1) propane dose. In each treatment, one subplot was hand-weeded in addition to flame treatment to remove differential weed effects, while the other received only the prescribed flame weeding regimen as weed control. Overall, control of broadleaf weeds was better than that of grass species. Broadleaf weed density and shoot mass were reduced as propane dose and the number of flame treatments increased. Grass density was reduced by 50% in all flamed treatments compared to the non-treated control, but no differences between flamed treatments were observed. Effects of flame treatments on grass shoot mass were minimal. Among weed-free treatments, onion was able to tolerate up to six flame treatments at either dose without a loss of yield. Treatments that received only flame weeding as weed control had total onion yields 37 and 80% of the weed-free flamed treatments in 2006 and 2007, respectively. Flame weeding treatments had little effect on the time to reach maturity, onion pungency, or quercetin concentration.

Changes in Flavor Precursors, Pungency, and Sugar Content in Short‐Day Onion Bulbs during 5‐Month Storage at Various Temperatures or in Controlled Atmosphere

Short-day onion bulbs (cv. TG 1015Y) were stored in 1% O(2,) 99% N(2) air at 5 °C (controlled atmosphere [CA]), or in ambient air at 5, 24, or 30 °C, for 5 mo. Changes in flavor precursors, pungency, and sugar content were investigated. After 5 mo of storage, 1-propenyl-L-cysteine sulfoxide concentrations increased continuously at 5 °C, gradually decreased in CA, slightly increased for 3 mo, and returned to initial levels at 24 °C and decreased below initial levels at 34 °C. Methyl-L-cysteine sulfoxide concentrations remained unchanged in all storage conditions. Onion pungency levels significantly increased at 5 °C, and decreased at 30 °C. Storage in CA and at 24 °C resulted in some fluctuations in pungency but the levels remained similar to initial levels. The calculated pyruvic acid concentrations were approximately 1.0 μmole/mL higher than the measured concentrations, and showed an increase at 5 °C and a slight reduction at 30 °C, consistent with the pungency results. Storage at 5 °C and in CA resulted in slight increases in fructose and glucose concentrations for 3 to 4 mo with subsequent rapid decreases, while sucrose concentrations remained unchanged. However, at 24 and 30 °C, fructose and glucose concentrations continuously decreased, accompanied by a continuous increase in sucrose concentrations. Storage in CA maintained the quality of onions best, as evidenced by the smallest changes in flavor precursors, pungency, and sugar concentrations, while storage at 5 °C resulted in increased pungency. Storage at 24 and 30 °C was tested for the purpose of comparison only; these temperatures are not recommended for commercial storage.

Underestimation of Pyruvic Acid Concentrations by Fructose and Cysteine in 2,4‐Dinitrophenylhydrazine‐Mediated Onion Pungency Test

Onion pungency has been routinely measured by determining pyruvic acid concentration in onion juice by reacting with 2,4-dinitrophenylhydrazine (DNPH) since 1961. However, the absorbency of the color adduct of the reaction rapidly decreased in onion samples as compared to that of the pyruvic acid standards, resulting in underestimations of the pyruvic acid concentrations. By measuring the absorbency at 1 min, we have demonstrated that accuracy could be substantially improved. As a continuation, the causes of degradation of the color adduct after the reaction and pyruvic acid itself before the reaction were examined in this study. Alliinase action in juice (fresh or cooked) and bulb colors did not influence the degradation. Some organic acids indigenously found in onion, such as ascorbic acid, proline, and glutamic acid, did not reduce the absorbency. However, fructose within the onion juice or supplemented caused the degradation of the color adduct, whereas sucrose and glucose had a lesser effect. Degradation rates increased proportionally as fructose concentrations increased up to 70 mg/mL. Cysteine was found to degrade the pyruvic acid itself before the pyruvic acid could react with DNPH. Approximately 90% of the pyruvic acid was degraded after 60 min in samples of 7 mM pyruvic acid supplemented with 10 mg/mL cysteine. Spectral comparisons of onion juice containing fructose naturally and pyruvic acid solution with supplemented fructose indicated identical patterns and confirmed that the color-adduct degradation was caused by fructose. Our study elucidated that fructose, a major sugar in onion juice, caused the degradation of color adduct in the onion pungency test and resulted in underestimation of the pyruvic acid concentration.

Antioxidants and Pungency of Onion

Information on levels of antioxidants and pungency can be utilized for improvement of onion (Allium cepa L.) through selection or breeding. Several genotypes were evaluated for these criteria. Phenol (128.51 mg/100 g) was found to be the most abundant antioxidant followed by ascorbic acid (11.49 mg/100 g). Superoxide dismutase, peroxidase, and catalase activities averaged as 4.80 mg·mL−1, 1.71 ΔA430·min−1·g−1, and 0.73 units, respectively. Antioxidant capacity, as determined by ascorbic acid and quercetin equivalents, was highest in ‘AVT-II(01)’ and ‘Sukhsagar’, whereas that determined by 2,2-diphenyl-β-picrylhydrazyl radical scavenging activity was highest (i.e., the lowest IC50 value) in ‘AVT-I(05)’. Lipid peroxidation, an indirect measure of antioxidant capacity, ranged between 0.019 and 0.036 μmol of malondialdehyde/100 g of substrate. Pyruvic acid development, an index of onion pungency, was between 6.86 and 15.33 μmol·g−1. Based on averages and principal component analysis, genotype ‘AVT-I(03)’ followed by ‘AVT-II(01)’ and ‘Sukhsagar’ can be used for future breeding programs.

Improved Consistency in DNPH‐Mediated Pyruvic Acid Analysis of Onion Juice by Modifying the Sample Processing Order

Onion pungency is commonly measured on absorbency of the wine pink color that results from adding NaOH to the heated mixture of dinitrophenylhydrazine (DNPH) and onion juice. However, significant variation exists among several modifications of the original Schwimmer and Weston (SW) method. We observed differences in pyruvic acid concentrations of 20%-30% between our automated method and a batch method with manual absorbency readings. To determine the source of the differences, we examined the heating time and waiting time of the sample-DNPH mixtures and found no differences. The differences were caused by differential color degradation between the pyruvic acid standards and onion juice samples. These differences could be minimized by reading the absorbency within 1 min of NaOH addition. Using this information, we devised the one-by-one method to control the reading time at 30 s. We compared 5 different analysis methods of 40 onion samples representing 4 onion colors. The automated, high-performance liquid chromatography, and SW methods had similar results, with only about a 5% difference. However, the batch method resulted in differences of approximately 24% as compared to the automated method. The one-by-one method produced very comparable results, within 5%, to the automated method. By modifying the procedure to ensure a uniform and fast reading time, we increased the consistency between the pungency analysis methods. Therefore, fast and uniform absorbency reading time is essential for an accurate measurement of pungency in undiluted onion juice.

Application of extra sulfur to high-sulfur soils does not increase pungency and related compounds in shortday onions

Sulfur (S) nutrition has a strong influence on onion pungency, and the production of sweet onions in the high-sulfur soil of Texas is a challenge to growers. This study was performed to determine the effects of S applications to fields already having sufficient levels of soil S on pungency and related compounds in four shortday onion cultivars. The onion cultivars ‘Cougar’, ‘Legend’, ‘Texas Early White’, and ‘Texas Grano 1015Y’ were grown in three commercial fields at Edinburg, Mercedes, and Weslaco of the Rio Grande Valley of South Texas with applications of sulfur at 0, 13, and 26 kg S/ha. Pyruvic acid, bulb weight, extractable S in soil and total S in bulb, soluble solids content (SSC), flavor precursor compounds [also called S-alk(en)yl- l-cysteine-sulfoxides (ACSOs)], and total sugars were measured. The pyruvic acid level of onions was not increased by the S applications and showed no significant correlation with soil S levels in any of the cultivars at locations having 30 or 235 ppm S. The SSC, total S in bulbs, total sugars, and total ACSO content also showed no correlation with the S applications and soil S levels. Onion pungency and content of flavor precursor compounds were significantly influenced by cultivar and cultivar × location interaction. We conclude that onion pungency is not increased by application of extra S fertilizer to commercial fields already containing sufficient levels of soil sulfur.

Characterization of Shortday Onion Cultivars of 3 Pungency Levels with Flavor Precursor, Free Amino Acid, Sulfur, and Sugar Contents

This study was conducted to characterize shortday onions of 3 pungency levels with regard to the composition of flavor related compounds. A total of 9 onion breeding lines/cultivars were selected, per each of low, medium, and high pungency level, with pyruvic acid contents of 1.9 to 2.8, 4.8 to 5.4, and 7.2 to 8.3 micromoles/mL, respectively. The contents of flavor precursors (S-1-propenyl-L-cysteine sulfoxide [1-PeCSO] and S-methyl-L-cysteine-sulfoxide [MCSO]), free amino acids, free sugars, soluble solids (SSC), and total sulfur (S) in onion bulbs were measured. The flavor precursor contents ranged from 0.03 to 0.16 mg/g fresh weight (FW) for MCSO, 0.07 to 0.65 mg for 1-PeCSO, and 0.12 to 0.77 mg in total, and precursor contents increased with the pungency levels. Onions of different pungency levels did not differ in the contents of individual or total free amino acids, and the most abundant amino acids were glutamine and arginine. The total sugar contents ranged from 50 to 75 mg/g FW, and total S contents (3.5 to 5.1 mg/g dry weight) were not correlated with the pungency levels. However, pungency levels were correlated inversely with bulb weight and positively with SSC, presumably by the effect of dilution. This study indicates that onion pungency is primarily determined by the content of flavor precursor compounds and not by total S, total sugars, or individual/total free amino acids in shortday bulbs.

A pyruvate dehydrogenase-based amperometric biosensor for assessing pungency in onions (Allium cepa L.)

A disposable prototype electrochemical biosensor was constructed using pyruvate dehydrogenase immobilised on mediated Meldolas Blue electrodes to determine pungency in onions (Allium cepa L.). The optimum operating potential was +50 mV vs. Ag/AgCl reference/counter electrode. The biosensor was able to differentiate between mild and pungent bulbs with pyruvate concentrations ranging between ≈4 and 8 mM in freshly extracted juices. Resolution was 0.5 mM and thus was comparable to the standard Schwimmer and Weston-based colorimetric assay currently employed by industry for determining pungency in macerated onion tissue.

Amount of characteristic compounds in 15 cultivars of onion (Allium cepa L.) in controlled field trials

AbstractBACKGROUND: In order to develop the production of sweet onions (Allium cepa L.) and onions with a high content of flavonols and fibre in Norway, it was necessary to evaluate available cultivars with respect to their content of selected chemical compounds. A field trial with 15 different cultivars was conducted at Landvik in southern Norway. Compounds that reflect onion pungency and sweetness (pyruvate, sugars) and parameters known to have a beneficial impact on health (fructo‐oligosaccharides (FOS), flavonols, antioxidant capacity) were analysed.RESULTS: The sweetest onions with respect to low content of pyruvate and high amount of fructose and glucose ranged in pyruvate content from 2.7 to 3.6 µmol mL−1. These cultivars were juicy and contained low amounts of FOS and total flavonols. The most pungent onions contained the highest amounts of FOS among the cultivars: 4.53, 3.80 and 5.81 g per 100 g fresh weight (FW) respectively. They also had a high content of flavonols (86.6, 159.2 and 97.6 mg per 100 g FW) and high dry weight content (14.6, 13.5 and 15.6 g per 100 g).CONCLUSION: The sweetest onion cultivars were found to be ‘NUN 9746’, ‘Musica’, ‘Domenica Supersweet’, ‘Colossus’ and ‘Cronus’. The most pungent cultivars were ‘Powell Brown’ and ‘Tilbury’, which also contained the highest amounts of flavonols and gave the highest Trolox equivalent antioxidant capacity (TEAC) values among the 15 cultivars. Copyright © 2007 Society of Chemical Industry

Subsurface drip irrigation of onions: Effects of drip tape emitter spacing on yield and quality

Improved irrigation water use efficiency is an important component of sustainable agricultural production. Efficient water delivery systems such as subsurface drip irrigation (SDI) can contribute immensely towards improving crop water use efficiency and conserving water. However, critical management considerations such as choice of SDI tube, emitter spacing and installation depth are necessary to attain improved irrigation efficiencies and production benefits. In this study, we evaluated the effects of subsurface drip tape emitter spacing (15, 20 and 30 cm) on yield and quality of sweet onions grown at two locations in South Texas—Weslaco and Los Ebanos. Season-long cumulative crop evapotranspiration (ETc) was 513 mm in Weslaco and 407 mm at Los Ebanos. Total crop water input (rain + irrigation) at Weslaco was roughly equal to ETc (92% ETc) whereas at Los Ebanos, water inputs exceeded ETc by about 35%. Onion yields ranged from 58.5 to 70.3 t ha −1 but were not affected by drip tube emitter spacing. Onion pungency (pyruvic acid development) and soluble solids concentration were also not significantly influenced by treatments. Crop water use efficiency was slightly higher at Weslaco (13.7 kg/m 3) than at Los Ebanos (11.7 kg/m 3) partly because of differences in total water inputs resulting from differences in irrigation management. The absence of any significant effects of drip tape emitter spacing on onion yield may be due to the fact that irrigation was managed to provide roughly similar irrigation amounts and optimum soil moisture conditions in all treatments.