Vidalia Onions Research Articles

First Report of Tomato spotted wilt virus in Leek (Allium porrum) in the United States

Tomato spotted wilt virus (TSWV) is a member of the family Bunyaviridae. It has many important crop hosts including tomato, pepper, tobacco, peanut, and onion. In Georgia, Vidalia onions (Allium cepa), a close relative of leek, can be infected by TSWV and Iris yellow spot virus (IYSV), which is another thrips-vectored tospovirus (2). For this reason, samples of leek transplants with virus-like symptoms in one field at the border of Georgia and Florida were tested for the presence of TSWV and IYSV. The transplants had been grown from seed in a greenhouse at the same location. The sampled plants exhibited extended bleaching of leaf tips and necrotic lesions. These symptoms were also seen on onion plants infected with TSWV and IYSV. The only natural infections of leek with IYSV have been reported thus far only from Reunion Island (4) and Slovenia (1), but to our knowledge, TSWV has not been reported as a pathogen of leek. Green tissue near the necrotic lesions and bleached tips of one symptomatic leaf per plant was sampled and analyzed using a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) (Agdia, Inc., Elkhart, IN). Of 90 plants tested, eight were positive for TSWV and none were positive for IYSV. Leek samples testing positive using ELISA were blotted onto FTA cards (Whatman Inc., Brentford, UK) to bind viral RNA for preservation and then processed according to the manufacturer's protocol. Punch-outs from the FTA cards were used for reverse transcription polymerase chain reaction (RT-PCR) with the TSWV-specific forward primer (5'-TTAAGCAAGTTCTGTGAG-3') and reverse primer (5'-ATGTCTAAGGTTAAGCTC-3') (3) to confirm the identity of TSWV. The primers are specific to the viral nucleocapsid gene. An amplicon of the expected size (774 bp) was produced from TSWV ELISA-positive leek plants, but not from healthy controls. TSWV has been found in many plants worldwide, but to our knowledge this is the first report of TSWV infecting leek. The effect that TSWV has on leek production is currently unknown.

DIRECT SEEDING VIDALIA ONIONS

The majority of Vidalia onions are produced as a transplanted crop. Seeding in high density plantings in September is followed 8 to 10 weeks later by transplanting to final spacing. This practice is labor intensive and expensive. Direct seeding would save on labor, cost, and time. Traditionally, transplanting has been done because of better winter survival, more uniform stands, and better irrigation management during seedling emergence. Beginning 5 years ago, we began evaluating direct seeding onions. Initially, seedstems (bolting) and lack of uniform stand establishment were the main problems. Sowing in September resulted in almost 100% seedstems and using a belt planter with raw seed resulted in poor singulation for uniform stand establishment. Mid-October ultimately proved to be the best time for sowing Vidalia onion seed. Earlier sowing resulted in more seedstems and later planting did not give the plants sufficient time to grow resulting in later stand loss during cold winter temperatures. Using polymer coated seed and a precision vacuum planter resulted in uniform, even stand establishment. Fertilizer requirements are almost half with direct seeded onions compared to transplanted onions with a reduction in the need for fungicides and herbicides. We have established direct seeded onions both with drip irrigation and overhead irrigation. There was concern that center-pivot irrigation would not be able to sufficiently irrigate fields during seedling establishment with the frequent hot fall days we experience. Since this work was initiated several growers have successfully produced direct seeded onions under center-pivot systems. Direct seeding Vidalia onions requires attention to detail because there is only one opportunity to get it right. Timing is also critical particularly with planting date and herbicide application.

PRELIMINARY FINDINGS ON PRODUCING ORGANIC VIDALIA ONIONS

There has been interest in producing Vidalia onions organically among both conventional and organic growers. In the 2000–01 season we began to look at producing onions organically. Starting with conventionally produced transplants that were transplanted at standard commercial spacings on beds prepared with 10.2–15.2 cm of incorporated compost and 2,802 kg·ha–1 rate of fresh poultry litter. This was sidedressed with an additional 2,500 less/acre (2,802 kg·ha–1) poultry litter. Yields were about half of conventional onion production. In 2002–03, production of organic transplants with 10.2 cm of incorporated compost with 2.24 t·ha–1 rate of poultry litter, which was followed by an additional sidedressing of 2.24 t·ha–1 rate of poultry litter resulted in similar findings. The weight of harvested transplants was about half that of conventionally produced transplants. In the 2002–03 and 2003–04 seasons various natural mulches were evaluated for weed control. They included wheat straw, oat straw, Bermuda hay, pine straw, and compost. None of these performed better than hand weeding and the wheat straw, oat straw, and Bermuda hay actually reduced yields apparently due to allelopathic effects. Finally in the 2003–04 season rates of poultry litter from 0–22.4 t·ha–1 were evaluated for transplant production with rates of 13.4, 17.9, and 22.4 t·ha–1 yielding plants comparable to conventional transplants. Work continues in the area of organic Vidalia onion production. One of the greatest challenge for future work will be finding a cost-effective and practical method of controlling weeds in transplant production.

EXPERIENCES WITH A FOOD PRODUCT X-RAY INSPECTION SYSTEM FOR CLASSIFYING ONIONS

Maintaining product quality is critical for success in fresh fruit and vegetable marketing. Some onionpackinghouses are considering the addition of x-ray inspection systems to their existing optical inspection systems. X-raysystems enable detection of voids that are likely to be associated with the presence of various bacterial or fungal rots in onions.A series of tests were conducted at the University of Georgia Vegetable and Vidalia Onion research and education center inToombs County, Georgia, with a commercially available x-ray inspection machine. In 2001, two 100-onion batches ofmedium-sized onions and 100 jumbo onions were machine-inspected, and then halved for a visual internal evaluation. In eachseries of tests, the accuracy rate was greater than 93% and the false positives were less than 6%. In 2002, two 100-onionbatches were run on a similar machine as in 2001. Additionally, in 2002 and 2004, multiple onions with slight to severe defectswere each passed through the inspection machine 50 times, respectively, with orientation not controlled to ascertainconsistency in defect detection. The machine passed onions with no to slight defect presence (based on subsequent internalvisual evaluation of onion halves) nearly 100% of the time. Onions with severe defects were rejected 100% of the time. In2004, a center rot disease (caused by Pantoea ananztis) study showed that 80% of bulbs that had passed a routine surfaceinspection and had been deemed to be diseased by the machine in fact exhibited the disorder on halving. False positives werein the 10% to 15% range. In the 2002 and 2004 studies, the machine detected bulbs with disease that passed human visualinspection (HVI) and (in 2004 only) individual tactile grading. These accuracy and false positive rates are very close to the90% and 10% levels generally accepted for these respective statistics. With appropriate addition of multiple lanes,commercially viable throughputs are possible.

The Consumers of Vidalia Onions

This study presents results of a survey of primary food shoppers who were consumers of sweet onions. The sample was stratified according to Vidalia onion shipments to five delineated regions of the United States, weighted by the U.S. Census. Results suggest that Vidalia onions are the preferred sweet onions, there is little away-from-home Vidalia onion consumption, and quality is of great importance. A low level of recall for Vidalia onion advertising was found. However, among the alternative forms of advertising, TV, newspaper, and in-store promotion were found to be more effective, especially the combination of newspaper inserts and in-store promotion.

First Report of Vidalia Onion (Allium cepa) Naturally Infected with Tomato spotted wilt virus and Iris yellow spot virus (Family Bunyaviridae, Genus Tospovirus) in Georgia.

Vidalia onion is an important crop in Georgia's agriculture with worldwide recognition as a specialty vegetable. Vidalia onions are shortday, Granex-type sweet onions grown within a specific area of southeastern Georgia. Tomato spotted wilt virus (TSWV) has been endemic to Georgia crops for the past decade, but has gone undetected in Vidalia onions. Tobacco thrips (Frankliniella fusca) and Western flower thrips (Frankliniella occidentalis) are the primary vectors for TSWV in this region, and a number of plant species serve as reproductive reservoirs for the vector or virus. Iris yellow spot virus (IYSV), an emerging tospovirus that is potentially a devastating pathogen of onion, has been reported in many locations in the western United States (2,4). Thrips tabaci is the known vector for IYSV, but it is unknown if noncrop plants play a role in its epidemiology in Georgia. During October 2003, a small (n = 12) sampling of onions with chlorosis and dieback of unknown etiology from the Vidalia region was screened for a variety of viruses, and TSWV and IYSV infections were serologically detected. Since that time, leaf and bulb tissues from 4,424 onion samples were screened for TSWV and IYSV using double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA) with commercial kits (Agdia Inc., Elkhart, IN). Samples were collected from 53 locations in the Vidalia region during the growing season between November 2003 and March 2004. Plants exhibiting stress, such as tip dieback, necrotic lesions, chlorosis or environmental damage were selected. Of these, 306 were positive for TSWV and 396 were positive for IYSV using positive threshold absorbance of three times the average plus two standard deviations of healthy negative onion controls. Positive serological findings of the onion tissues were verified by immunocapture-reverse transcription-polymerase chain reaction (IC-RT-PCR) for TSWV (3) and RT-PCR for IYSV (1). In both instances, a region of the viral nucleocapsid (N) gene was amplified. The PCR products were analyzed with gel electrophoresis with an ethidium bromide stain in 0.8% agarose. Eighty-six percent (n = 263) of the TSWV ELISA-positive samples exhibited the expected 774-bp product and 55 percent (n = 217) of the IYSV ELISA-positive samples exhibited the expected 962-bp product. The reduced success of the IYSV verification could be attributed to the age and deteriorated condition of the samples at the time of amplification. Thrips tabaci were obtained from onion seedbeds and cull piles within the early sampling (n = 84) and screened for TSWV by the use of an indirect-ELISA to the nonstructural (NSs) protein of TSWV. Of the thrips sampled, 25 were positive in ELISA. While the incidence of IYSV and TSWV in the Vidalia onion crop has been documented, more research is needed to illuminate their potential danger to Vidalia onions.

Farmer‐owned brands?

AbstractThis report lays out the economic arguments in favor of the establishment of farmer‐owned brands in Midwestern agriculture and presents four case studies based on successful efforts in this area in the European Union and the United States. The case studies involve Parma Ham, Brunello di Montalcino wine, Vidalia onions, and a third‐party verification organization. The case studies show that these brands can be profitable for farmers, and emphasize the importance of restricting the supply of any successful brand. One of the case studies shows that this type of supply control can run afoul of antitrust regulations. [EconLit citations: Q130, Q180, R580.] © 2004 Wiley Periodicals, Inc. Agribusiness 20: 269–285, 2004.

Impacts of Advertising and Promotion on the Demand for Scanned Purchases of Vidalia Onions

This study evaluates the advertising and promotion impacts on the demand for scanned purchases of Vidalia onions and estimates returns to such expenditures. The analysis uses supermarket scanner data collected from scanned purchases of Vidalia onions and advertising and promotion expenditure data generated by the Vidalia Onion Marketing Order. An error components model is estimated to determine the impacts of advertising and promotion expenditures for scanned purchases of Vidalia onions, own price, prices of substitutes and complements, demographics, and seasonal variables for 10 different markets over a 260-week period from 1996 to 2001. Results indicate that sales of other onions have a negative impact on demand for Vidalia onions, income has a positive impact, and other vegetables may be complements to Vidalia onions. Advertising and promotion expenditures yielded a positive return to Vidalia onion producers in the period studied.

First Report of a Leaf Blight of Onion Caused by Xanthomonas spp. in Georgia.

In October of 2001 and 2002, a leaf blight was reported affecting Vidalia onion (Allium cepa) cvs. Pegasus and Sweet Vidalia, respectively, in one field each. Lesions on onion seedlings began as a water-soaked, tip dieback that gradually blighted the entire leaf. Symptoms on onion transplants appeared as elongated, water-soaked lesions that typically collapsed at the point of initial infection. In both cases, disease was very severe on seedlings, and disease incidence was 50% or more in both fields. Warm temperatures combined with overhead irrigation and above average rainfall likely enhanced the severity and spread of disease. Disease was not detected on more mature onions once cool, dry conditions occurred later in the season, and no significant economic loss occurred. Seed was tested from seed lots of the aforementioned cultivars and Xanthomonas spp. were not found. Diseased tissue was macerated in sterile, phosphate-buffered saline, and 10 μl of the resulting suspension was streaked on nutrient agar plates. Yellow-pigmented, gram-negative, rod-shaped bacteria were isolated routinely from diseased tissue. Bacteria were catalase-positive, cellulolytic, oxidase-negative, amylolytic, proteolytic, and utilized glucose in an oxidative manner. Analysis of whole cell, fatty acid methyl esters (FAME) using the Microbial Identification System (MIS, Sherlock version 3.1; MIDI, Inc., Newark, DE) identified four representative strains of the bacterium as a pathovar of Xanthomonas axonopodis (similarity indices 0.75 to 0.83). Known Xanthomonas spp. from onion from Colorado and Texas (1,2) had similar FAME profiles when analyzed by the MIDI system. Onion plants were grown under greenhouse conditions for 2 months and inoculated by injecting the base of a quill with 1.0 ml of bacterial suspensions (1 × 107 CFU ml-1) of the Xanthomonas sp. isolated from Georgia, and negative controls were inoculated with 1 ml of sterile water. Disease symptoms developed on plants inoculated with bacterial suspensions in 4 to 7 days and Xanthomonas sp. was isolated from the lesions produced. Disease symptoms occurred when the same suspension was sprayed on onion foliage. No symptoms occurred on plants inoculated with 1 ml of sterile water. To our knowledge, this is the first report of Xanthomonas spp. affecting Vidalia onions.

DOES BOTRYTIS ALLII SPREAD FROM INFECTED ONIONS TO SOUND ONIONS IN CONTROLLED ATMOSPHERE STORAGE?

Approximately one-half of the low pungency, sweet onions produced in the Vidalia onion growing area of Georgia, USA, are stored in CA (3% O2 + 5% CO2) to extend the marketing period. In some years, losses during storage caused by Botrytis allii are large. To determine if B. allii spreads in storage, sound onions, bruised onions and onions with open cuts were stored in air and CA along with onions which had been inoculated externally with B. allii. B. allii grew in the inoculated onions during storage at 1 °C in air and CA. B. allii also spread from externally infected onions to bruised onions and onions with open cuts in contact with them, but did not spread to sound onions. Pure cultures of B. allii and B. cinerea grew on potato dextrose agar (PDA) more slowly in CA than in air at 0 °C. B. allii growing on PDA did not produce spores at 0 °C, but did produce spores at 10 °C and 20 °C in air but not in CA. B. cinerea produced spores in both air and CA storage. Since spread of B. allii through the air is by spores, it is unlikely that the fungus spreads to sound onions in CA storage except by direct contact with infected onions.

Flavonoids and antioxidant capacity of Georgia-grown Vidalia onions.

Vidalia onion varieties Nirvana, DPS 1032, Yellow 2025, King-Midas, and SBO 133 grown at Vidalia, Georgia, were analyzed for flavonoid content. A high-performance liquid chromatographic (HPLC) method with photodiode array detection was used for quantification. Compounds were analyzed as aglycons after acid hydrolysis with 1.2 M HCl. Identification of each compound was based on comparison of its retention time and UV spectra with those of pure commercial standards. Three major flavonoids, kaempferol, myricetin, and quercetin, were identified and quantified. Quercetin was the major flavonoid (7.70-46.32 mg/100 g fresh weight, FW) present in all varieties, followed by myricetin (2.77-4.13 mg/100 g FW). Minor quantities of kaempferol (1.10-1.98 mg/100 g FW) were also detected. The total polyphenols and Trolox equivalent antioxidant capacity (TEAC) ranged from 73.33 to 180.84 mg/100 g FW and 0.92-1.56 microM TEAC/g FW, respectively. A positive but weaker correlation was obtained for total polyphenols versus antioxidant capacity. Nevertheless, a stronger correlation (r(2) = 0.34) was obtained between flavonoid content versus antioxidant capacity. The data indicate that Vidalia onions are a rich source of quercetin, and they also contain myricetin and kaempferol.

Vidalia Onions—Sweet Onion Production in Southeastern Georgia

Southeastern Georgia is ideal for sweet onion (Allium cepa) pro duction. This region is noted for its mild winters, low sulfur soils, and abundant water supply. Vidalia onions with their national reputation for mildness have dramatically increased in availability in the last 10 to 12 years. Several factors have contributed to this increase including; national name recognition, regulatory control of the Vidalia name, ideal region of production, Marketing Order 955 (USDA, 1989), and the adoption of controlled atmosphere (CA) storage. These factors have resulted in a 3-fold increase in production since 1989 (USDA, 2001). The growth of the Vidalia onion industry has not been without challenge or controversy. Wide fluctuations in performance from one year to the next have caused CA storage not to be as consistent as expected for extending onion shelf life. In addition, some growers have expressed concern over some new varieties being too hot to be called Vidalia onions. Other varieties have increased problems with late season diseases. Vidalia onions, however, remain one of the bright spots in American agriculture by providing good returns for the producers. Although somewhat uncertain, the Vidalia onion’s future remains promising. For the industry to continue to prosper issues concerning, increased competition, production problems including variety selection, and use of CA storage have to be addressed. Vidalia onions are also referred to as yellow onions, salad onions, green onions, and dry bulb onions. In order to be a Vidalia onion they must be a yellow Granex type. Salad and green onions refers to immature onions. They are comparable to scallions, however they tend to be longer in total length with larger leaves and an expanded bulb, about 1 inch (2.5 cm). The objective of this article is to highlight the Vidalia onion industry, and to describe its past, present and future with respect to production practices, issues of concern, and marketing.

Evaluation of Plant-bed Fertility in Vidalia Onions

In 1998–99, experiments were conducted to evaluate current fertility practices with plant-bed onions. In experiments in 1998 and 1999, a factorial experiment of preplant 5–10–15 and CaNO3 sidedressing indicated that CaNO3 had a significant effect on foliar nitrogen levels. CaNO3 also had an effect on stand count in 1998, but not in 1999. CaNO3 and 5–10–15 had an effect on plant height in both 1998 and 1999, with an interaction between 5–10–15 and CaNO3 in 1999. In 1999, transplants were also evaluated on an acceptability scale with 5–10–15 and CaNO3 rates resulting in significant differences in transplant acceptability. Postseedling applications of high phosphorus fertilizer were also evaluated. There were no consistent improvements in transplant growth with applications of high phosphorus fertilizers, such as 18–46–0 or 10–34–0, either on soils with very high residual phosphorus (242 lb/acre) or medium residual phosphorus (50 lb/acre). In addition, variety was not a factor in these responses.

Metam Sodium Use in Vidalia Sweet Onions

Metam sodium has been evaluated on onions in Georgia since the mid-1980s for control of various soil pathogens in the production of transplants. Observations also indicated excellent weed control activity. Further work showed significant growth response of transplants, 90% or better weed control, and efficacy of Phoma terrestris, Fusarium, and Pythium. Results were better in comparison studies than found with methyl bromide, chloropicrin, and other fumigation combinations. This led to use of the product in field production of dry bulb onions. Seven years of studies revealed an average yield increase of 190 bushels per acre over the control, even where Phoma terrestris levels were minimal. Today, almost all transplant production includes the use of metam sodium and field use is beginning to be used by growers. With limited crop rotation being practiced in the Vidalia onion belt, metam sodium will continue to play a major role in controlling the ever-increasing levels of Phoma terrestris and maintaining profitability in onion production in Georgia.

Modelling Moisture Loss of Onions in Storage Using Moisture Loss Information Obtained from Individually Measured Onions

Vidalia onions were grown following recommended cultural practices in 1994-1996 and they were harvested at early, optimum, or late maturity. After onions were cured for various lengths of time, a random sample of onions was marked for individual measurement. All onions were placed into either low or high humidity A/C controlled storage for up to 30 weeks. Onions were removed as they showed signs of being rotten. Initially, and every 2 weeks thereafter, weight and grade data were collected from individual onions and in bulk from other onions. There were up to 96 treatment combinations each year. Using individual onion data, simulation of the weight loss of the bulked onions was done. Although over 5,000 onions were involved, individual measurements were taken on only 1,920 onions over the 3 years. Five simulations were conducted using parameters derived from individual onion data. Results of the simulations resembled the actual weight loss trends within the specified 90% confidence range.