Long-day Onion Research Articles

First Report of Pantoea ananatis and Pantoea eucalypti causing onion leaf blight and bulb decay in Central Chile.

Nearly 5,400 hectares of long-day onions (Allium cepa) are cultivated in the Central Zone of Chile (UTM 33°3´S to 37°24´S). During summer 2021-22 and 2022-23 (December to February), followed by high temperatures (around 35°C) and high humidity conditions, symptoms showing yellowing, soft rot, blight on old leaves, necrotic tips, and soft bulbs were observed. The affected plants were observed in "spots" into the fields, and the incidence reached 5-10%. The severity was high, and 70-80% of the affected plants died. Symptomatic plants from different fields from the Coquimbo, Metropolitan, O´Higgins and Maule regions were sampled. Isolations were made using casamino-acid peptone glucose (CPG) agar medium (Schaad, 2001). Yellow-pigmented, circular to irregular shaped colonies were observed. Molecular identification was carried out by partial 16S rRNA gene sequencing, resulting in the identification of 18 isolates of Pantoea spp. from twelve different fields. Selected strains were biochemically analyzed using the GEN III BIOLOG microtest system (Hayward, CA) and were identified as Pantoea spp. BLAST analyses of the 16S rRNA sequences (602 nt) of selected strains (GenBank Accession No. OR527817 to OR527819) against the NCBI Database resulted in the identification of Pantoea species with 100% coverage and 100% identity. To determine the Pantoea species of each strain, housekeeping gene gyrB (Delétoile et al. 2009) was amplified and sequenced (GenBank Accessions No. OR544061 to OR544063). BLAST analysis (802 nt) of selected strains resulted in 100% coverage and 100% identity, identifying three different species: P. ananatis, P. eucalypti, and P. agglomerans. Pantoea species were isolated from both leaves and bulbs and no more than one species was observed per field. Pathogenicity assays in onion plants and bulbs were performed based on the methodology described by Asselin et al. (2018). Five onion plants cv. Cimarron of thirteen-week-old were inoculated by wounding an external leave with a sterile toothpick previously immersed in a bacterial suspension at ~ 108 CFU/mL and maintained at 26-28°C for 30 days in high humidity conditions. Control plants were inoculated with sterile water. Plants inoculated with Pantoea spp. showed chlorosis, soft rot, and necrosis mainly in older leaves, as observed in the field, while negative control plants remained healthy. Pantoea spp. were re-isolated from the inoculated onion plants. Toothpicks dipped in the inoculum were stuck 4 cm into the shoulders of onion bulbs and incubated at 26°C for 20 days. Water was inoculated as a negative control. At the end of the incubation period, the bulbs were opened longitudinally across their inoculation sites and shrunken, brownish, watery scales were observed. Pantoea species have been previously described as causing leaf blight of onions in Georgia and Michigan in the USA and South Africa, Brazil, and Uruguay (Hattingh and Walters 1981; Gitaitis and Gay 1997; Edens et al. 2006; Tho et al. 2015; De Armas et al. 2022; Rosende et al. 2022). P. agglomerans was recently reported in Chile (Sepúlveda et al. 2023), but this is the first report of P. ananatis and P. eucalypti affecting onions in central Chile. This detection is an alert call for the onion's growers and exporters in Chile for upcoming seasons, where conditions predisposing to disease may continue to occur. It is crucial to continue analyzing the factors that caused the appearance of this new disease in onions.

Reactions of Short, Intermediate and Long Day Onion Genotypes in Turkish National Onion Breeding Program to Fusarium Basal Rot Disease

Onion basal rot (Fusarium oxysporum f. sp. cepae) disease exerts serious threats on global onion (Allium cepa L.) production and trade. Present breeding programs mostly focus on development of cultivars resistant to onion basal rot disease. Characterization of breeding material in breeding gene pool is the first step of breeding. This study was conducted to determine the susceptibility of 4 onion cultivars, 30 long-day, 1 intermediate-day and 21 short-day onion genotypes to onion basal rot disease. Significant differences were seen in disease susceptibility of the genotypes (P<0.01 ) in both onion seedling and bulb tests. Onion seedling and bulb tests revealed that resistance was not detected in short and intermediate-day onion genotypes and cultivars, while two of long-day onion genotypes (ACLD 7 and 8) were found to be tolerant. Based on present finding, 3 cultivars, 28 long-day, 1 intermediate-day and 21 short-day genotypes were identified as sensitive. ACLD 7 and 8 long-day onion genotypes, which were identified as promising in seedling tests, were also identified as tolerant in bulb tests and such findings proved the compliance of seedling and bulb tests. Bulbs were obtained from the long-day onion lines (ACLD 7-8 genotypes) that were found to be promising and survived in seedling tests and seeds were obtained from these genotypes to ensure progress of generation and they were included in breeding gene pool.

Agronomic, Physiological, Genetic and Phytochemical Characteristics of Onion Varieties Influenced by Daylength Requirements

The evaluation of A. cepa biodiversity provides onion breeders with great prospects to obtain plants with high resistance to environmental factors, remarkable yield, and product quality. Genetic diversity assessment of a collection of nine short- and long-day onion landraces and varieties originated from different Iranian regions, using ISSR markers and UPGMA dendrograms, was carried out for the first time. Short-day landraces (Sarze, Sarkoreh, and Kerman) originated from low latitude and short-day hybrids (Mirela and Soberana) demonstrated high genetic similarity, in terms of physiological responses to day length and temperature during the crop cycle and bulbing stage initiation. Contrarily, high latitude landraces (Azarshahr, White Gorgan, Kurdistan, and Esfahan) showed low biometrical, agronomic and genetic similarity with commercial short-day onions. Specific differences in morphological reactions between these two groups displayed diverse responses of plants to day length and temperature. Long- and short-day cultivars displayed significant differences in the dynamics of leaf and scale number, leaf and root length, dry and fresh weight, and bulbing ratio and bulb diameter, which were in accordance with ISSR data. The local landraces Azarshahr, Kurdistan, and Esfahan had high antioxidant status, suggesting high prospects for their utilization as an alternative to foreign F1 hybrid varieties.

Targeted Metabolome Profiling of Indonesian Shallots and Japanese Long-Day/Short-Day Bulb Onions

In this study, targeted metabolome analysis was applied to identify the discriminative metabolites between Indonesian shallot landraces, Japanese long-day onion (LDO) varieties, and Japanese short-day onion (SDO) varieties. In total, 172 metabolite signal intensities were subjected to multivariate PLS-DA, VIP, and random forest modeling to gain further insight into genotype-specific metabolites. PLS-DA divides the examined genotypes into three different clusters, implying that shallot landraces exhibited a distinct metabolite profile compared with Japanese LDO and SDO varieties. The PLS-DA, VIP, and random forest results indicated that the shallot and LDO are richer in metabolite constituents in comparison with the SDO. Specifically, amino acids and organosulfur compounds were the key characteristic metabolites in shallot and LDO genotypes. The analysis of S-alk(en)yl-L-cysteine sulfoxide (ACSO) compounds showed higher accumulation in the shallot landraces relative to LDO and SDO varieties, which explains the stronger pungency and odor in shallots. In addition, the LDO showed higher ACSO content compared with the SDO, implying that long-day cultivation might enhance sulfur assimilation in the Japanese onion. The LDO 'Super Kitamomiji' and the shallots 'Probolinggo' and 'Thailand' showed higher ACSO content than other varieties, making it useful for Allium breeding to improve the flavor and stress tolerance of onions.

Onion Yield and Internal Quality Increased by Straw Mulch and Reduced by Artificial Heat, but Not Affected by Kaolin Particle Film

Onion (Allium cepa L.) bulbs produced in the Pacific Northwest of the United States in 2014 and 2015 had unusually high incidence of internal decay. This decay was not detectable externally, leading to marketing problems when bulbs were packed and shipped to markets. The onion growing seasons in 2014 and 2015 were unusually hot, suggesting a connection of heat stress to bulb internal decay. Field studies to investigate the effect of temperature on onion bulb internal decay and yield were conducted in 2016–18 with drip-irrigated onions at the Oregon State University, Malheur Experiment Station located in eastern Oregon. Two long-day onion cultivars were submitted to four cultural practice variations to affect soil and bulb temperatures: bare soil check, supplemental heat using electric heat cables, white kaolinite clay application to the bulb sides and soil surface, and wheat (Triticum aestivum L.) straw mulch. The treatments established significant midafternoon average bulb and soil surface temperature gradients in the following order of increasing temperature: straw mulch, kaolinite, check, and supplemental heat. Averaged over years and cultivars, straw-mulched onions had the highest yield of bulbs larger than 102 mm diameter. Averaged over years and cultivars, onions receiving supplemental heat had the lowest total and marketable yield with no difference among the other treatments. Straw mulched onions had higher total and marketable yield than the bare soil check treatment in 2017, the hottest year. Averaged over the 3 years and two cultivars, marketable yield and yield of bulbs larger than 102 mm diameter decreased with increasing midafternoon bulb temperatures. Kaolinite application did not increase bulb yield nor bulb size compared with the bare soil check. The incidence of internal bulb decay was low all 3 years. In 2017, onions receiving supplemental heat had the highest internal decay and the straw-mulched onions had among the lowest internal decay. There was little difference in the measured soil moisture among treatments. Straw mulching may attenuate the negative effects of excessive heat on yield and bulb internal quality for long day onion production.

Performance of Onion Cultivars in the Treasure Valley of Eastern Oregon and Southwestern Idaho in 2010–20

Each year ≈24,000 acres of onions (Allium cepa) are produced in the Treasure Valley of eastern Oregon and southwestern Idaho, which accounts for 20% of U.S. dry-bulb onion acreage. Onions in this region are long-day onions and are irrigated by either furrow irrigation or drip irrigation, with drip irrigation having become the predominant system in the past 10 years. Onion production in the Treasure Valley faces many biotic pressures and changing market conditions that renders cultivar development and testing of critical importance to the onion industry. Direct-seeded yellow, white, and red onion cultivars have been evaluated yearly at the Malheur Experiment Station, Oregon State University, in Ontario, OR, USA, since 1975. From 2010 to 2020, 10 onion seed companies participated in the trials. There were 21 to 32 yellow cultivars, two to 10 red cultivars, and one to seven white cultivars entered in the trial each year. Only five cultivars were entered all 11 years. Total yields for the yellow cultivars ranged from an average of 680 cwt/acre in 2010 to 1277 cwt/acre in 2018, and averaged 961 cwt/acre over the 11 years. Yield of yellow bulbs larger than 4 inches (colossal and super colossal) ranged from 13% in 2010 to 61% in 2018, and averaged 34% over the 11 years. Single centered yellow bulbs ranged from 46% in 2013 to 70% in 2014. Total yields for the red cultivars averaged 520 cwt/acre and total yield of white cultivars averaged 988 cwt/acre over the 11 years. Over the 11 years, single-centered bulbs of red cultivars averaged 65% and single-centered bulbs of white cultivars averaged 45%. Some newer cultivars show improvements in single centeredness, resistance to Iris yellow spot virus, and yield of larger bulbs over cultivar Vaquero, which was released in 1993, indicating the success of breeding efforts. Yields of five yellow cultivars that were in the trials every year since 2010, increased over time. This increase can be partly attributed to improvements in cultural practices over the years: adoption of drip irrigation, more intensive nutrient management, refined onion thrips (Thrips tabaci) control, and higher plant population.

Determination of Emergence and Seedling Characteristics in One- and Two-Year Seeds of Some Long-Day Onion (Allium cepa L.) Varieties

The most important factors are the seed quality and vigor in which determine the yield and quality of vegetable production. Seed quality is affected by many factors such as seed development on the mother plant, genetic characters of species, and variety, storage conditions, etc. Onion (Allium cepa L.) has a seed that is easily deteriorating. Therefore one-year seed use is commonly recommended. In this research, which was conducted to determine the effect of the production year and variety on seed emergence and seedling properties was used one- and the two-year seed of four long-day variety (denotes A, B, C or D). As result, it was determined that the seedling morphological characters were not affected by production year and one-year seeds had a higher emergence percentage and vigor index than two-year seeds. The highest emergence rates were seen in variety D (95.50%) for one-year seeds and in variety A (80.00%) for two-year seeds. Among vigor indexes, the highest values were observed in variety C (2.85) for one-year seeds and variety A (2.39) for two-year seeds. Also, seed viability and viability decreasing rate were different according to varieties.

Changes in the expression of photoperiodic bulbing genes in response to increasing daylength in long-day and short-day onion varieties

ABSTRACT Onion bulb initiation is photoperiod-dependent. Understanding this is crucial for adapting new varieties for growth at different latitudes, as well as aiding germplasm screening for the choice of current varieties. This study aims to gain further understanding of the molecular mechanisms involved in onion bulbing process based on the parallels with well-characterised functional clock genes in the Arabidopsis flowering pathway. A comprehensive set of diurnal quantitative expression experiments was carried out to investigate the bulbing response in two different onion varieties, namely Renate, a long-day variety and Hojem, a short-day variety under increasing intermediate day-lengths. All onion homologous to Arabidopsis flowering time genes showed clear diurnal expression patterns peaking at different times of the day for both long/short-day onions, indicating their role in daylength dependent bulbing process at molecular level. Under intermediate daylengths, AcFT1 expression level increased with daylengths in both varieties, while AcFT4 was expressed in all daylengths. The two genes showed complementary expression with AcFT4 peaking in the morning and AcFT1 in the evening in longer days. The results indicate that AcFT1 and AcFT4 are negatively co-regulated, but AcFT1 is the predominant regulator of bulb formation in response to daylength.

The role of organ - and daylength - specific gene expression in bulb development and resource management in onion (ALLIUM CEPA L.)

Onion development is a complex process with each developmental event depending on the adequate supply of resources. Also, these resource components themselves are crucial nutrients in onion when consumed as food. For higher yield and better quality in onion production, it is essential to not only have a high level of photosynthesis but also effective transportation of photosynthetic products. A comprehensive set of spatial and developmental time-course experiments detailed the gene expression in onion leaf and bulb tissues during the development of a long-day onion cultivar under long-day and short-day conditions. Candidates included well characterised functional clock genes in Arabidopsis flowering pathway, as well as some novel sequences differentially expressed in bulb tissues. Both AcFT1 and AcFT4 showed significant increasing expression level during plant development, with AcFT1 being expressed in long-days during bulb formation and AcFT4 in short-days where bulbs are not formed. The data further support the role of AcFT1 as a promoter and AcFT4 as inhibitor in onion bulb formation. A number of genes associated with onion carbohydrate metabolism, sulphur metabolism and bulb development were identified as having different tissue-specific expression and provide targets for future studies.

Optimizing sowing date for short- and long-day onion

ABSTRACT Bulb development of onion (Allium cepa L) varieties exhibit different reactions to sowing date, day length, and temperature. Short- and long-day onions exhibit different reactions to day length and temperature at sowing date as it affects bulb development. Seed of short-day ‘Mirela’ and ‘Es13022ʹ, and long-day ‘White Gorgan’ was sown on 2 March and 29 October 2017 to investigate vegetative development. October sown onion had greater vegetative yield. ‘Mirela’ and ‘Es13022ʹ had wider bulbs than ‘White Gorgon’ for both sowing dates. Short-day onion accessions ‘Mirela’ and ‘Es13022ʹ reached the greatest vegetative development earlier than long-day ‘White Gorgan.’ Short–day varieties sown in October could be suitable for off-season production.

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.

Diurnal expression of Arabidopsis Gene homologs during daylength-regulated bulb formation in onion (Allium cepa L.)

Bulb initiation in long-day onion is regulated at the physiological level in a similar way to the photoperiodic regulation of flowering in Arabidopsis. This study establishes in onion, the diurnal time-course expression, in onion, of key genes particularly linked to circadian regulation in Arabidopsis. The long-day onion variety ‘Renate’ and the short-day (SD) onion variety ‘Hojem’ were used for these experiments. Onion plants were grown under natural LD conditions in the Phytobiology Glasshouse and immediately after bulbing they were transferred to two SANYO 2279 controlled environment cabinets for 10 d providing constant LD (16 h photoperiod including 8 h fluorescent followed by 8 h incandescent light) and constant short days (8 h photoperiod with fluorescent light). Five FLOWERING LOCUS T (FT) and three CONSTANS-LIKE (COL) genes were identified in onion, including two novel COL sequences through RNA-Seq analysis. The new AcCOL2 shows a diurnal pattern of expression similar to Arabidopsis CONSTANS (CO). Allium cepa FLAVIN-BINDING, KELCH REPEAT, F-BOX PROTEIN 1 (AcFKF1), Allium cepa GIGANTEA (AcGI) and AcCOL2 showed good diurnal expression patterns consistent with photoperiod sensing and regulation of AcFT1. All FT genes exhibited different diurnal expression patterns peaking at different times of the day. Notably, AcFT1 was expressed in the later part of the day which is very similar to the expression of Arabidopsis FT, while AcFT4 was expressed late in the night and the early morning in both Renate and Hojem varieties of onion, with the caveat that, AcFT4 is under less stringent daylength control in Hojem than in Renate. The timing of the peaks and expression pattern in both Renate F1 and Hojem suggest that AcFT5 may be under circadian or diurnal regulation under LD conditions and AcFT6 might not be circadian or diurnally regulated. These findings will help to understand the basis of the difference between responses of onions adapted to different latitudes, which is important for developing new varieties.

Annualization of the Long Day Onion Breeding Cycle through Threshold Vernalization and Dormancy Disruption

Background: Genetic gain is a function of several parameters including generation time. Onion is a biennial crop that typically requires two full calendar years per generation or breeding cycle. Annualization of onion breeding could double the rate of genetic gain but is technically difficult because of bulb vernalization and dormancy requirements. Methods: Based on recent results that demonstrate vernalization thresholds for long-day onion, we conducted an experiment to assess whether shorter vernalization times could result in faster, uniform flowering with dormancy-broken onion bulbs. Bulbs from eight varieties were subjected to a 15% hydrogen peroxide treatment for 4 h in order to break dormancy. This treatment was followed by either 6 or 12 weeks of vernalization after the first physical signs of dormancy release. The vernalized plants were transferred to 16-h daylengths in a 20 °C greenhouse for flowering. Results: The treatments imposed in this study resulted in the completion of a full generation in less than 12 months for all eight varieties examined. As the length of vernalization at 10 °C increased, we observed greater uniformity in floral initiation and a higher proportion of scape emergence. Plants that were vernalized for 6 weeks flowered 24% earlier than those in the 12-week treatment group. However, we observed greater uniformity in scape emergence both within and among varieties when vernalized for 12 weeks. conclusions: We have developed a framework for an annual cycle breeding system that offers the ability to phenotype bulb traits. We have also identified aspects of the system that will benefit from further refinements. Overall, this annualization system may be useful for advancing generations in onion breeding and reducing the time required to produce new varieties.

Efficacy of Molecular Markers Jnurf13 and AcPms1 for Prediction of Genotypes at the Nuclear Ms Locus in Three Open-pollinated Populations of Onion from North America

Seed of hybrid onion (Allium cepa L.) is produced using cytoplasmic male sterility (CMS). For the most widely used source of onion CMS, male sterility is conditioned by the interaction of male sterile (S) cytoplasm and the homozygous recessive genotype at the nuclear male fertility locus Ms. Because of the biennial generation time of onion, classical crossing and segregation analyses take years to establish cytoplasms and genotypes at Ms. Numerous molecular markers have been developed to distinguish onion cytoplasms and estimate genotypes at Ms. Two nuclear markers (jnurf13 and AcPms1) have been reported to cosegregate with Ms and correctly predict genotypes in commercial breeding lines and diverse onion germplasm; however, these markers were less predictive for open-pollinated (OP) populations from India. We evaluated the efficacy of jnurf13 and AcPms1 to correctly classify genotypes at Ms using 144 random plants from three OP populations of long-day onion from North America. No recombination events were detected between AcPms1 and the Ms locus and three events occurred between jnurf13 and Ms. Our results support either marker as a useful tool to predict genotypes at Ms in North American populations of onion, with AcPms1 being the better of the two.

Response of Onion Yield, Grade, and Financial Return to Plant Population and Irrigation System

Onion (Allium cepa) plant population is an important factor in total yield and bulb size, both of which can influence economic return to growers. Different onion bulb marketing opportunities influence the plant populations that growers should target. With the transition from furrow irrigation to a drip irrigation system, growers have doubts as to the onion population that should be planted to assure favorable economic outcomes. Onions were grown on silt loam at the Oregon State University Malheur Experiment Station, Ontario, OR in 2011 and 2012 following bread wheat (Triticum aestivum L.) each year. Long-day onion cultivars Vaquero, Esteem, Barbaro, and Sedona were planted heavily and thinned to nominal plant populations between 222,000 and 593,000 plants/ha under furrow irrigation, subsurface drip irrigation, and “intense bed” subsurface drip irrigation. The intense bed configuration had 50% more rows of onions with three drip tapes per 1.94-m bed instead of two tapes. The experiment had a randomized complete block split-split-plot design with six replicates. Irrigation systems were the main plots, cultivars the split plots, and plant populations the split-split plots. Onion yield and grade responses to plant population for each cultivar and each planting system were determined by regression of yield and grade on the actual onion plant stands. In general, there were few differences among irrigation systems or interactions among irrigations systems, cultivars, and plant populations. Averaging over cultivars, total and marketable bulb yield out of storage increased with plant population, whereas the bulb diameters decreased with plant population. Average marketable yield was 119 Mg⋅ha−1 over the 2 years. Average yield of colossal bulbs >102 mm in diameter decreased with increasing plant population. In 2011, estimated gross economic return increased linearly with plant population, offset in part by increasing seed cost. In 2012, estimated economic return responded quadratically to plant population with maximum return of $45,357/ha at 419,000 plants/ha.

Successful deployment of marker assisted selection (MAS) for inbred and hybrid development in long-day onion (Allium cepaL.)

In the present investigation, male sterile and maintainer lines were identified using molecular markers in three long day onion populations. Molecular markers, 5’cob and orfA501 were able to distinguish effectively normal (N) and sterile (S) cytoplasm in all the three populations. The observed frequency of S cytoplasm in VL Piaz 67 (100%),VL Piaz3 (86.4%) and KR1 (90%) was higher than N cytoplasm. Out of the two PCR markers viz., OPT and PsaO used to determine the nuclear fertility restorer locus (Ms locus), OPT was found better than PsaO. Increased frequency of dominant homozygous alleles (87.4%) followed by heterozygous alleles (8.6%) and homozygous recessive alleles (4.0%) was observed. Fertility/sterility of plants were validated by acetocarmine staining of the pollens and correlated with observations made using molecular markers. Out of the three populations studied, only 12 plants (2.15%) happened to be completely male sterile in VL Piaz-3 and KR1 population, whereas there was no male sterile plant observed among the population in VL Piaz 67. Selfing and test crossing of plants having normal (N) cytoplasm led to the development and identification of maintainer lines in VL Piaz3 and KR1 population. This is the first example of deploying DNA markers for identification and purification of male sterility and hybrid development in long day onion in Indian population.

Overwintering Potential of Onion in Kentucky

Eight cultivars of onion (Allium cepa) representing, long, intermediate, and short-day types were evaluated for their ability to be overwintered in Kentucky. Onion seedlings were transplanted in Nov. 2007 and Oct. 2008. Plants were covered with spunbonded rowcovers or wheat (Triticum sp.) straw mulch in December and mature bulbs were harvested in June and July. Bulbing was initiated in ‘Yellow Granex’ (short-day) during transplant production, thus it was not planted in the field in either year of the experiment. The use of rowcovers compared with straw mulch increased survival rates in all cultivars. The intermediate-daylength cultivars, Candy, Superstar, and Expression, had greater percentages of bolting when grown under rowcovers compared with straw mulch. This resulted low marketable yields despite high survival rates. Rowcover/mulch treatment and cultivar interacted (P ≤ 0.05) to affect yields. The long-day cultivars, Olympic, Ailsa Craig, and Walla Walla had the highest yields when grown under rowcovers. ‘Olympic’, the highest yielding cultivar, produced a large percentage of jumbo-sized bulbs. The short-day cultivar, WI-131, had low survival rates and yields under rowcovers and straw mulch. Pungencies were lowest in ‘WI-131’ and ‘Olympic’. In general, long-day onion cultivars had high rates of survival, low rates of bolting, and higher yields compared with intermediate-day types. This suggests that they would be preferred for overwinter production in Kentucky.

Effects of transplanting time and plant density on yield, quality and antioxidant content of onion (Allium cepa L.) in southern Italy

The aim of this research was to evaluate the effects of four transplanting times (1 February, 16 February, 3 March, 18 March) and three plant densities (21.2, 27.2 and 38.1ptm−2) on the growth, productivity and bulb quality indicators (size, dry weight, soluble solids content, sugars, acids, amino acids, antioxidants, mineral composition) of long-day onion crops, cultivar “Ramata di Montoro”.Crop yield, bulb mean weight and calibre decreased significantly from the earliest to the latest transplanting time. Plant density did not affect production significantly but the most spaced crop (21.2ptm−2) produced bulbs of the biggest size.The bulb quality indicators responded differently to transplanting time: dry weight, glucose, fructose, raffinose, citric and malic acids and vitamin C content did not change; soluble solids content, sucrose, and oxalic acid increased from the 1 February to the 18 March transplanting time, while pyruvic acid, calcium, chlorides and nitrates content decreased. The sequence of transplanting times resulted in complex pattern of variations of the mineral composition and of the free amino acid content of the bulbs. The bulb total polyphenol content did not vary with the transplanting time and it was about 7mgg−1 dry weight, with the outer skins containing more than double polyphenols compared to the inner fresh scales.This research on “Ramata di Montoro” onion has shown that early transplanting increases bulb yield and size, whereas some aspects of bulb quality improve with late transplants.

High-Quality and Long-Storability of F1 Hybrid Long-Day Onion ‘Daekwanhwang’

High-Quality and Long-Storability of F1 Hybrid Long-Day Onion ‘Daekwanhwang’

High-Quality and Long-Storability of F1 Hybrid Long-Day Onion ‘Daekwanhwang’

High-Quality and Long-Storability of F1 Hybrid Long-Day Onion ‘Daekwanhwang’