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

in HortTechnology
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  • 1 Malheur Experiment Station, Oregon State University, 595 Onion Avenue, Ontario, OR 97914, USA

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.

Abstract

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.

Onions (A. cepa) have been produced commercially in the Treasure Valley of eastern Oregon and southwestern Idaho for more than 100 years. Each year ≈24,000 acres of onions are produced in the Treasure Valley, which accounts for 20% of U.S. dry-bulb onion acreage. These are mostly direct-seeded long-day (“Sweet Spanish”) onions. Onions are marketed out of the field starting at harvest in August and September and out of storage through April.

Onion production in the Treasure Valley faces many biotic pressures that renders cultivar development and testing of critical importance to the onion industry. Onion thrips (T. tabaci) is the most important arthropod pest of onions in the Treasure Valley (Reitz, 2014). Feeding by onion thrips reduces the photosynthetic capacity of plants, which leads to reduced bulb size and quality. Onion thrips control management has changed over time in response to research at the Malheur Experiment Station, Oregon State University, Ontario, OR, USA.

The main soil-borne diseases in the Treasure Valley are pink root caused by a fungus (Setophoma terrestis) that infects onion roots, and Fusarium basal rot, caused by a fungus (Fusarium oxysporum) that infects the onion bulb basal plate. Most growers use 4- to 5-year crop rotations to help reduce disease pressure, but these pathogens are highly persistent in the soil and can still infect when fields are replanted to onion. Consequently, growers still rely on soil fumigation and other pesticides to reduce the impact of soil-borne diseases.

Iris yellow spot virus (IYSV) has been among the most important factors influencing onion yield since it first appeared in the Treasure Valley in the early 2000s (Gent et al., 2006; Mohan and Moyer, 2004). IYSV is transmitted to onion plants by feeding of onion thrips. Infection of onion plants by IYSV results in loss of photosynthetic leaf area. Severe infection with IYSV can result in complete loss of foliage, resulting in poor storage quality because the onion neck does not fall over and cure thoroughly. Breeding efforts are attempting to develop cultivars resistant to IYSV (Boateng et al., 2014).

Abiotic factors have also caused changes in onion production practices. Onions in the Treasure Valley are irrigated by either furrow irrigation or drip irrigation, with drip irrigation having become the predominant system in the past 10 years. Besides improving bulb size uniformity, drip irrigation allows for more frequent and precise water and nutrient applications. Changing market conditions have prompted growers to target different bulb sizes. In the late 1990s, the popularity of whole onion appetizers resulted in an increase in the production of bulbs larger than 4¼ inches in diameter (super colossal) through reductions in plant population. Lately, the market for super colossal bulbs has diminished, prompting growers to increase plant populations. Bulb single centeredness has become an important cultivar characteristic for the onion industry. Single centeredness is a heritable trait that allows for the development of cultivars with a high frequency of single centers (Gamie et al., 1995; Wall et al., 1996).

Seed companies are continuously releasing new cultivars bred to tolerate new pest and disease pressures and bred for improved quality characteristics. The availability of new cultivars enhances the importance of university trials in assisting growers’ cultivar selections under changing biotic and abiotic circumstances. Direct-seeded yellow, white, and red onion cultivars have been evaluated yearly at the Malheur Experiment Station since 1975. Cultivars are evaluated in the field for plant disease, onion thrips damage, maturity, bolting (flowering), and bulb single centers. Out of storage, the cultivars are evaluated for yield, grade, and bulb decomposition. Each year, growers and seed industry representatives have the opportunity to examine the cultivars at an Onion Variety Field Day in late August and during bulb evaluations in January. Results of the cultivar trials at the Malheur Experiment Station have been reported in HortTechnology previously (Shock et al., 2000a, 2005, 2008). This report presents data for onion cultivars from 2010 to 2020. Cultivar Vaquero has been in the cultivar trials at the Malheur Experiment Station every year since it was released in 1993 and can be used as a standard for comparisons. Cultivar reports for individual years are available on the Malheur Experiment Station website (Oregon State University, 2022).

Materials and methods

Onions were grown on Owyhee silt loam (coarse-silty, mixed, mesic, Xerollic Camborthids) or Greenleaf silt loam (fine-silty, mixed, mesic, Xerollic Haplargids) with a pH ≈7.5. The fields were in a 5-year rotation with onions grown every fifth year following wheat (Triticum aestivum). Some years, rotations also included sweet corn (Zea mays), potato (Solanum tuberosum), and soybean (Glycine max). After wheat was harvested, the stubble was shredded and the fields were irrigated to sprout unharvested wheat kernels and then the fields were disked. Before fall plowing, the fields were fertilized based on soil analyses for nutrients besides nitrogen (N), which is applied in the growing season to avoid leaching. Starting in 2017, in addition to the chemical fertilizer, 10 tons/acre of composted cattle manure was broadcast before plowing in the fall. Based on analyses of the manure, averaged over the years 2017 to 2019, 193 lb/acre N, 140 lb/acre phosphorus (P), and 353 lb/acre potassium (K) were added from the manure each year. After plowing, the fields were formed into beds 22 inches wide (center to center) and fumigated within the bed with 64 lb/acre a.i. of metam sodium (Vapam; Amvac Chemical Corp., Newport Beach, CA, USA).

Ten seed companies have participated in the trials since 2010 (Table 1). Decisions on which cultivar to enter each year are made by the seed companies. Consequently, there was yearly variation in the cultivars in the trials. Only cultivars that were in the trials 5 years or more are included in this paper. From 2010 to 2018, all cultivars of all bulb colors were planted in one trial. Starting in 2019, the cultivars were planted in three adjacent trials based on bulb color (yellow, white, red) to allow separate harvests and statistical analyses. The experimental design each year was a randomized complete block with five replicates. The seed was planted as close as possible to the middle of March in plots four double rows wide and 27 ft long (Table 2).

Table 1.

Seed companies participating in the Oregon State University onion cultivar trials conducted at Ontario, OR, USA.

Table 1.

A high seeding rate and thinning were used to provide uniform plant populations. Seed was planted in double rows spaced 3 inches apart at an in-row spacing of nine seeds per foot. One double row was planted on each 22-inch bed. Planting was done with customized planter units equipped with disc openers (Flex Planter; John Deere and Co., Moline, IL, USA). Most seed companies provided fungicide-treated seed to control damping off. Not all seed companies provided insecticide-treated seed, so immediately after planting, the fields received a narrow band of chlorpyrifos (Lorsban 15G; Corteva Agriscience, Calgary, AB, Canada) over the seed rows at 0.82 lb/acre a.i. for preventive control of onion maggot (Delia antiqua) and the soil surface was cultipacked. Onion emergence started in early April. About mid-May, alleys 4 ft wide were cut between plots, leaving plots 23 ft long. The seedlings were hand thinned in mid-May at the two- to three-leaf growth stage. From 2010 to 2012, the seedlings were thinned to a target spacing of 6 inches between individual onion plants in each single row, or 95,000 plants/acre. Because of a reduction in the market for super colossal bulbs (>4.25 inches), starting in 2013 the seedlings were thinned to a target spacing of 4.75 inches between individual onion plants in each single row, or 120,000 plants/acre.

From 2010 to 2014, the trial was furrow irrigated. Starting in 2015, the trial was drip irrigated with tape laid at 4-inch depth between pairs of beds during planting. The drip tape had emitters spaced 12 inches apart and an emitter flow rate of 0.22 gal/min per 100 ft (Aqua-Traxx; Toro Co., El Cajon, CA, USA). The distance between the tape and the center of each double row of onions was 11 inches. This distance was possible because of the favorable lateral wetting properties of the soils.

Furrow irrigations were run manually using a soil water tension (SWT) irrigation onset criterion of 25 cbar (Shock et al., 1998a). Drip irrigations were run automatically using an SWT irrigation onset criterion of 20 cbar (Shock et al., 2000b). SWT was measured with eight granular matrix sensors [GMSs (Watermark Soil Moisture Sensors Model 200SS; Irrometer Co. Inc., Riverside, CA, USA)] installed at 8-inch depth in the center of the double row of onions. Sensors had been calibrated to SWT (Shock et al., 1998b).

For the drip irrigations, the GMSs were connected to a datalogger that recorded the SWT every hour. The datalogger automatically made irrigation decisions every 12 h. The fields were irrigated if the average of the eight sensors was at an SWT of 20 cbar or higher. Irrigation durations were 8 h, 19 min to apply 0.48 inch of water. The automated drip irrigation systems were started in late April and irrigations ended in early September.

The onions were managed to minimize yield reductions from weeds, pests, diseases, water stress, and nutrient deficiencies using standard commercial practices. Most years, glyphosate herbicide (Roundup PowerMax; Bayer Cropscience, St. Louis, MO, USA) was applied before onion emergence. For weed control after onion emergence, the following herbicides were broadcast yearly: oxyfluorfen (GoalTender; Dow AgroSciences, Indianapolis, IN, USA), bromoxynil (Brox 2EC; Albaugh LLC, Ankeny, IA, USA), pendimethalin (Prowl H2O; Bayer Corp., Research Triangle Park, NC, USA), clethodim (Shadow 3EC; Arysta LifeScience North America, Cary, NC, USA), and sethoxydim (Poast; BASF Corp., Research Triangle Park, NC, USA). In addition to herbicide applications, hand weeding was done as necessary to maintain the field weed free.

Seven insecticides were used for onion thrips control (Tables 3 and 4). Insecticide applications were made every 7 to 10 d from late May to early August, totaling 5 to 10 applications per year. Insecticide applications were made by foliar ground applications until approximately late June when excessive onion plant height required a switch to aerial applications. Starting in 2019, a high-boy boom sprayer allowed insecticide applications to be made by foliar ground applications all season.

Table 2.

Dates for planting, emergence, lifting, topping and bagging, and start of storage in the Oregon State University onion cultivar trials conducted at Ontario, OR, USA.

Table 2.
Table 3.

Insecticides applied for onion thrips control in the Oregon State University onion cultivar trials conducted at Ontario, OR, USA.

Table 3.

In-season onion nutrition was based on root tissue and soil samples. When the trial was furrow irrigated, in-season nutrient applications were limited to sidedressing in May and later in the furrow irrigation water. Furrow irrigation complicated frequent in-season applications, so nutrient management was less intensive and based on infrequent soil and tissue samples and standard amounts of N applied. When the trial was drip irrigated, root tissue and soil samples were taken every week starting in early June from field borders. Root tissue and soil samples were analyzed for nutrients by Western Laboratories, Inc., Parma, ID, USA. Root tissue was analyzed for nitrate concentration and soil was analyzed for concentrations of nutrients in the soil solution. Nutrients judged to be deficient according to extension guidelines (Sullivan et al., 2001) were applied each week through the drip tape. Nitrogen was applied through the drip tape as urea ammonium nitrate solution.

In late August, onions were evaluated for IYSV symptom severity. Evaluations of IYSV symptom severity were done by rating onions in each plot on a subjective scale of 0 to 5 of increasing severity of IYSV symptoms: 0 = no symptoms, 1 = 1% to 25% of foliage was diseased, 2 = 26% to 50% of foliage was diseased, 3 = 51% to 75% of foliage was diseased, 4 = 76% to 99% of foliage was diseased, and 5 = 100% of foliage was diseased.

Onions in each plot were evaluated for maturity at the beginning of August and again, typically 2 weeks later in mid-August. Maturity was evaluated subjectively by visually rating the percentage of onions with the tops down and the total percent of dry leaves in the plot. The number of bolted onions in each plot was also counted.

All onions from the middle two double rows in each 23-ft-long plot were harvested for yield evaluations. The red cultivars were topped and the bulbs placed in burlap bags to dry in the field (curing) in late August because of earlier maturation than the yellow and white cultivars. The red cultivars were allowed to cure for ≈7 d and then were put in storage. After undercutting of the roots (lifting) in early September, the yellow and white cultivars were cured for ≈7 d in the field, then were topped, bagged, and placed in storage. The storage shed was ventilated and the temperature was slowly decreased to maintain air temperature as close to 34 °F as possible. Onions were graded out of storage in early January.

During grading, bulbs were separated according to external quality: bulbs without blemishes (No. 1s), split bulbs (No. 2s), bulbs with neck rot (Botrytis allii), bulbs with Fusarium basal rot (Fusarium oxysporum), bulbs with black mold (Aspergillus niger), and bulbs infected with unidentified bacteria in the external scales. The No. 1 bulbs were graded according to diameter: small (<2.25 inches), medium (2.25–3 inches), jumbo (3–4 inches), colossal (4–4.25 inches), and super colossal (>4.25 inches). Marketable yield consisted of No.1 bulbs larger than 2.25 inches.

After harvest, bulbs from one of the border rows in each plot of both trials were rated for single centers. Twenty-five consecutive onions ranging in diameter from 3.5 to 4.25 inches were cut equatorially through the bulb middle and separated into single-centered and multiple-centered bulbs. The multiple-centered onions were ranked according to the diameter of the first entire single ring: small had diameters less than 1.5 inches, medium had diameters from 1.5 to 2.25 inches, and large had diameters greater than 2.25 inches.

Because there was yearly variation in the cultivars entered, cultivar differences were determined using analysis of variance for each year separately. Means separation was determined using a protected Fisher’s least significant difference test at the 5% probability level.

Results and discussion

In all years, except 2011 and 2017, onion seed was planted in the last 2 weeks of March (Table 2). In 2011 and 2017, onion planting was delayed until April because of excessively wet soils. On average, emergence occurred on 12 Apr and it took 20 d from planting for seedlings to emerge.

Total amounts of N applied varied each year, but generally, half as much was applied with drip irrigation than with furrow irrigation (Table 5). This is consistent with a survey of N fertilizer use and onion yields in growers fields in the Treasure Valley under furrow and drip irrigation (Klauzer and Shock, 2005). With drip irrigation, the frequent root tissue and soil sampling allowed fertilizer amounts to be more easily adjusted. Most years, soil available N and soil solution N remained below critical levels until late June, when large increases occurred. These soil N increases are consistent with previous studies showing high N mineralization rates in Treasure Valley soils (Stieber et al., 1995). Generally, N applications were ended in late June because of the large increases in soil N at this time.

Table 4.

Number of insecticide applications and products applied for onion thrips control by year in the Oregon State University onion cultivar trials conducted at Ontario, OR, USA.

Table 4.
Table 5.

Irrigation method and total amounts of nitrogen (N) applied during the growing season in the Oregon State University onion cultivar trials conducted at Ontario, OR, USA.

Table 5.
Table 6.

Total yield after 3 mo. of storage for yellow onion cultivars from 2010 to 2020 in the Oregon State University cultivar trials conducted at Ontario, OR, USA.

Table 6.

Onion thrips management in the cultivar trial has changed over time and has been based on results of research at the Malheur Experiment Station. Until 2007, synthetic pyrethroids, such as lambda-cyhalothrin (Warrior; Syngenta Crop Protection, Greensboro, NC, USA), and carbamates, such as methomyl, were the main insecticides used for onion thrips control in the cultivar trial. In the early 2000s, research at the Malheur Experiment Station started showing evidence that onion thrips populations were becoming tolerant to synthetic pyrethroids (Jensen, 2006, 2007). The use of pyrethroids in the cultivar trial was discontinued in 2007. In 2018, research started showing evidence of resistance to methomyl (Reitz et al., 2019), and its use was discontinued for onion thrips control in the cultivar trial in 2019. To slow the development of insecticide resistance, an onion thrips control strategy based on rotations of insecticides with different modes of action with no more than two consecutive applications with the same mode of action has been implemented. The number of insecticides with different modes of action used for onion thrips control has increased from two in 2010 to six in 2020 (Tables 3 and 4). The number of insecticide applications has also increased over time.

Data for the yellow cultivars can be found in Tables 6 to 10 and red and white cultivar data can be found in Tables 11 to 15. Total yields for the yellow cultivars ranged from 680 cwt/acre in 2010 to 1277 cwt/acre in 2018, and averaged 961 cwt/acre over the 11 years. Yield of yellow colossal and super colossal bulbs (larger than 4 inches) ranged from 13% in 2010 to 61% in 2018, and averaged 34% over the 11 years, and single-centered bulbs ranged from 46% in 2013 to 70% in 2014. Total yields for the red cultivars ranged from 297 cwt/acre in 2010 to 662 cwt/acre in 2017 and 2019, and averaged 520 cwt/acre over the 11 years. Over the 11 years, yield of red bulbs larger than 3 inches (jumbo, colossal, super colossal) averaged 63% and single-centered bulbs averaged 65%. Over the 11 years, total yield of white bulbs averaged 988 cwt/acre and single-centered bulbs averaged 45%.

Table 7.

Marketable yield after 3 mo. of storage as a percentage of total yield for yellow onion cultivars from 2010–20 in the Oregon State University cultivar trials conducted at Ontario, OR, USA.

Table 7.
Table 8.

Yield of colossal plus super colossal bulbs after 3 mo. of storage as a percentage of total yield for yellow onion cultivars from 2010 to 2020 in the Oregon State University cultivar trials conducted at Ontario, OR, USA.

Table 8.
Table 9.

Percentage of single-centered bulbs for yellow onion cultivars from 2010 to 2020 in the Oregon State University cultivar trials conducted at Ontario, OR, USA.

Table 9.
Table 10.

Iris yellow spot virus (IYSV) symptom severity for yellow onion cultivars in 2014 and 2015 in the Oregon State University cultivar trials conducted at Ontario, OR, USA.

Table 10.
Table 11.

Total yield after 3 mo. of storage for red and white onion cultivars from 2010 to 2020 in the Oregon State University cultivar trials conducted at Ontario, OR, USA.

Table 11.
Table 12.

Marketable yield after 3 mo. of storage as a percentage of total yield for red and white onion cultivars from 2010–20 in the Oregon State University cultivar trials conducted at Ontario, OR, USA.

Table 12.
Table 13.

Yield of jumbo plus colossal plus super colossal bulbs after 3 mo. of storage as a percentage of total yield for red onion cultivars from 2010 to 2020 in the Oregon State University cultivar trials conducted at Ontario, OR, USA.

Table 13.
Table 14.

Yield of colossal plus super colossal bulbs [> 4 inches (10.2 cm) diameter] after 3 mo. of storage as a percentage of total yield for white onion cultivars from 2010 to 2020 in the Oregon State University cultivar trials conducted at Ontario, OR, USA.

Table 14.
Table 15.

Percentage of single-centered bulbs for red and white onion cultivars from 2010 to 2020 in the Oregon State University cultivar trials conducted at Ontario, OR, USA.

Table 15.
Table 16.

Average total yield, yield of bulbs larger than 4 inches (10.2 cm) diameter, and bulb single centers for 11 cultivars from 2015 to 2020 in the Oregon State University cultivar trials conducted at Ontario, OR, USA.

Table 16.

Total yields were higher after the switch to drip irrigation, except in 2015, a year with higher IYSV pressure. Drip irrigation has also resulted in an increase in bulbs larger than 4 inches and in a reduction in medium and jumbo bulbs. These results are in agreement with studies comparing onion productivity under drip and furrow irrigation (Halvorson et al., 2008; Shock et al., 2011). Wohleb and Waters (2016) reported on onion cultivar trials in the Columbia Basin of Washington State, an onion production region similar to ours, in 2012, 2013, and 2014. Total yields for the yellow, red, and white cultivars in our study are lower than in the Washington State trials for the same years and the same cultivars. This difference might be because of the different irrigation systems that were used in the two locations. The Washington State trials used drip irrigation in 2012, and sprinkler irrigation in 2013 and 2014, whereas our trials used furrow irrigation in the same years. Total yields in our trials after the switch to drip irrigation in 2015 are similar to total yields in the Washington State trials for the same cultivars.

In only five of the 11 years did some cultivars have statistically significant higher total yield than cultivar Vaquero, which was released commercially in 1993. To compare newer cultivars with Vaquero, an analysis of variance was done for 11 cultivars that were in the trials all years from 2015 to 2020. Averaged over those 6 years, ‘SV6672’, ‘Joaquin’, and ‘Vaquero’ had the highest total yield, which highlights the total yield stability of ‘Vaquero’ (Table 16). However, cultivars SV6672 and Joaquin had a higher percentage of bulbs larger than 4 inches than Vaquero averaged over the 6 years.

The total yield increases over time may also be partly attributed to the increase in plant population from 95,000 to 120,000 plants/acre in 2013. Research at the Malheur Experiment Station has shown that marketable yield increases with increasing plant population up to the highest tested of 150,000 plants/acre (Shock et al., 2004).

Bulb single centeredness, which is an important quality characteristic for onion ring processors, ranged from an average of 46% in 2013 to 70% in 2014 for the yellow cultivars. Averaged over the 11 years, the percentage of single-centered bulbs for the yellow cultivars averaged 58%, higher than the averages of 21%, 29%, and 26% in the cultivar trials at the Malheur Experiment Station in 2000, 2001, and 2002, respectively (Shock et al., 2005). This increase in average single centeredness could be due to improved breeding efforts for single centeredness by seed companies. Most of the cultivars in the trials in 2000–02 have been discontinued. In nine of the 11 years from 2010 to 2020, one or more cultivars had a statistically significant higher percentage of single centers than cultivar Vaquero (Table 9), which also can be indicative of breeding efforts. Cultivar Arcero had a higher percentage of single centers than Vaquero in 8 of the 11 years of the trials. For the 11 cultivars in the trials from 2015 to 2020, Arcero and Joaquin had a higher average percentage of single centers than Vaquero (Table 16). This is in agreement with the Washington State cultivar trials in which Arcero and Joaquin had a higher percentage of single centers than Vaquero averaged over 3 years (Wohleb and Waters, 2016).

Bolting for the yellow and white cultivars was low during the 11 years of trials. Bolting was not observed in any cultivar in 2011, 2012, 2015, and 2017. Bolting for the red cultivars only occurred in 2013, 2014, and 2018 and did not exceed 0.2% of bulbs.

IYSV was first observed in the cultivar trial starting in 2004. Thereafter, lower yields could be partly explained by high IYSV severity. Since 2010, IYSV severity of 2 (26% to 50% of foliage diseased) or higher only occurred in the cultivar trials in 2014 and 2015 (Table 10). In 2014, three cultivars had statistically significant lower IYSV severity than Vaquero. In 2015, several cultivars had lower IYSV severity than Vaquero. In both 2014 and 2015, cultivars Joaquin and 16000 had lower IYSV severity than Vaquero. In the 2005 and 2006 cultivar trials at the Malheur Experiment Station, Joaquin also had lower IYSV symptom severity than Vaquero and had among the lowest IYSV symptom severity (Shock et al., 2008). IYSV severity for the red cultivars averaged 2.3 in 2014 and 2.9 in 2015, with no statistically significant difference among cultivars. In the other years, IYSV severity for all cultivars was low with a severity of one and most cultivars showing only one or two lesions per plant. Other factors also contributed to lower yields. In 2011, delayed planting, due to wet soils and a cool summer resulted in lower yields.

Total yields for five cultivars (Sedona, Legend, Arcero, Joaquin, and Vaquero), which were entered in all years of the trials since 2010, have increased over time (Fig. 1). The yield increases starting in 2013, compared with 2010 to 2012, can be partly attributed to the increase in plant population in 2013. The increased yields also can be partly attributed to the adoption of drip irrigation in 2015, leading to more precise irrigation management and more intensive nutrient management. Improved onion thrips control was probably another contributing factor in higher yields.

Fig. 1.
Fig. 1.

Linear regression of average total yield of onion cultivars Sedona, Legend, Arcero, Joaquin, and Vaquero against year since 2010 in the Oregon State University cultivar trials conducted at Ontario, OR, USA; 1 cwt/acre = 112.0851 kg·ha−1.

Citation: HortTechnology 32, 5; 10.21273/HORTTECH05061-22

The results of the trials indicate that in terms of yield and bulb size, Vaquero performed as well as newer cultivars. However, in terms of bulb single centeredness and resistance to IYSV, some of the newer cultivars performed better than Vaquero.

The long-term ongoing nature of the trial allows growers to evaluate which cultivars are most suitable for their farms. Expanding data collected to include information on susceptibility to pests and diseases and soil/tissue testing for nutrients increases the benefits of the trial to growers in how to manage different cultivars on their farms. In addition, these ongoing trials can assist breeders in efforts to breed for resistance/tolerance to pests.

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Literature cited

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  • Shock, C.C., Barnum, J. & Seddigh, M. 1998b Calibration of Watermark soil moisture sensors for irrigation management Proc. XIX Intl. Irr. Show. San Diego, CA, USA 1–3 Nov. 1998 139 146

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    • Export Citation
  • Shock, C.C., Ishida, J.K., Eldredge, E.P. & Seddigh, M. 2000a Yield of yellow onion cultivars in eastern Oregon and southwestern Idaho HortTechnology 10 613 620 https://doi.org/10.21273/horttech.10.3.613

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  • Shock, C.C., Feibert, E.B.G. & Saunders, L.D. 2000b Irrigation criteria for drip-irrigated onions HortScience 35 63 66 https://doi.org/10.21273/hortsci.35.1.63

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  • Shock, C.C., Feibert, E.B.G. & Saunders, L.D. 2004 Plant population and nitrogen fertilization for subsurface drip-irrigated onion HortScience 39 1722 1727 https://doi.org/10.21273/hortsci.39.7.1722

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  • Shock, C.C., Feibert, E.B.G. & Saunders, L.D. 2005 Single-centered and super colossal bulbs from yellow onion cultivars HortTechnology 15 399 408 https://doi.org/10.21273/horttech.15.2.0399

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  • Shock, C.C., Feibert, E., Jensen, L., Mohan, S.K. & Saunders, L.D. 2008 Onion variety response to Iris yellow spot virus HortTechnology 18 539 544 https://doi.org/10.21273/horttech.18.3.539

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  • Shock, C.C., Feibert, E., Saunders, L.D., Jensen, L., Mohan, S.K., Sampangi, R. & Pappu, H. 2011 Management of onion cultural practices to control the expression of Iris yellow spot virus Oregon State Univ., Malheur Exp. Sta. Annu. Rpt., Dept. of Crop and Soil Sci. Ext/CrS 132 23 41

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  • Stieber, T.D., Shock, C.C., Feibert, E., Thornton, M., Brown, B., Cook, W., Seyedbagheri, Mir-M. & Westerman, D.T. 1995 Nitrogen mineralization in Treasure Valley soils. 1993 and 1994 results Oregon State Univ., Malheur Expt. Sta. Spec. Rpt. 947 194 207

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  • Sullivan, D.M., Brown, B.D., Shock, C.C., Horneck, D.A., Stevens, R.G., Pelter, G.Q. & Feibert, E.B.G. 2001 Nutrient management for sweet Spanish onions in the Pacific Northwest Pacific Northwest Ext. Publ. PNW 546 1 26

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    • Export Citation
  • Wall, M.M., Mohammad, A. & Corgan, J.N. 1996 Heritability estimates and response to selection to the pungency and single center traits in onion Euphytica 87 133 139 https://doi.org/10.1007/bf00021886

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  • Wohleb, C.H. & Waters, T.D. 2016 Yield, quality, and storage characteristics of onion cultivars in the Columbia Basin of Washington in 2012–14 HortTechnology 26 230 243 https://doi.org/10.21273/horttech.26.2.230

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Contributor Notes

This project was funded by the Idaho-Eastern Oregon Onion Committee, cooperating onion seed companies, Oregon State University, the Malheur County Education Service District, and supported by Formula Grant nos. 2020-31100-06041 and 2020-31200-06041 from the U.S. Department of Agriculture, National Institute of Food and Agriculture.

E.F. is the corresponding author. E-mail: erik.feibert@oregonstate.edu.

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    Linear regression of average total yield of onion cultivars Sedona, Legend, Arcero, Joaquin, and Vaquero against year since 2010 in the Oregon State University cultivar trials conducted at Ontario, OR, USA; 1 cwt/acre = 112.0851 kg·ha−1.

  • Boateng, C.O., Schwartz, H.F., Havey, M.J. & Otto, K. 2014 Evaluation of onion germplasm for resistance to iris yellow spot (Iris yellow spot virus) and onion thrips, Thrips tabaci Southwest. Entomol. 39 237 260 https://doi.org/10.3958/059.039.0218

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  • Gamie, A.A., Ahmed, F.A., El-Kafury, A.K.I. & Abd El-Rehim, G.H. 1995 Suitability of S3 progeny of single center Shandaweel 1 onion for bulb production from sets at Sohag. Assiut J Agro Sci. 26 73 80

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  • Gent, D.H., du Toit, L.J., Fichtner, S.F., Mohan, S.K., Pappu, H.R. & Schwartz, H.F. 2006 Iris yellow spot virus: An emerging threat to onion bulb seed production Plant Dis. 90 1468 1480 https://doi.org/10.1094/pd-90-1468

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  • Halvorson, A.D., Bartolo, M.E., Reule, C.A. & Berrada, A. 2008 Nitrogen effects on onion yield under drip and furrow irrigation Agron. J. 100 1062 1069 https://doi.org/10.2134/agronj2007.0377

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  • Jensen, L 2006 Insecticide trials for onion thrips (Thrips tabaci) control-2005 Oregon State Univ., Malheur Expt. Sta. Spec. Rpt. 1070 90 98

  • Jensen, L 2007 Insecticide efficacy trial for thrips control in dry bulb onions Oregon State Univ., Malheur Expt. Sta. Spec. Rpt. 1075 54 58

  • Klauzer, J. & Shock, C. 2005 Growers use less nitrogen fertilizer on drip-irrigated onion than furrow-irrigated onion Oregon State Univ., Malheur Expt. Sta. Spec. Rpt. 1062 94 96

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  • Mohan, K. & Moyer, J.W. 2004 Iris yellow spot virus in onion seed and bulb crops Phytopathology 94 6 S153 (abstr.)

  • Oregon State University 2022 Onion variety trials 1995-2020 28 Jul 2022. <https://agsci.oregonstate.edu/mes/publications/station-complete-annual- reports>

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  • Reitz, S.R 2014 Onion thrips (Thysanoptera: Thripidae) and their management in the Treasure Valley of the Pacific Northwest Fla. Entomol. 97 349 354 https://doi.org/10.1653/024.097.0202

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  • Reitz, S., Trenkel, I., Wieland, K., Shock, C.C., Feibert, E.B.G. & Rivera, A. 2019 Thrips and Iris yellow spot virus management in the Treasure Valley Oregon State Univ., Malheur Exp. Sta. Annu. Rpt., Dept. of Crop and Soil Sci. Ext/CrS 161 116 133

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  • Shock, C.C., Feibert, E.B.G. & Saunders, L.D. 1998a Onion yield and quality affected by soil water potential as irrigation threshold HortScience 33 1188 1191 https://doi.org/10.21273/hortsci.33.7. 1188

    • Search Google Scholar
    • Export Citation
  • Shock, C.C., Barnum, J. & Seddigh, M. 1998b Calibration of Watermark soil moisture sensors for irrigation management Proc. XIX Intl. Irr. Show. San Diego, CA, USA 1–3 Nov. 1998 139 146

    • Search Google Scholar
    • Export Citation
  • Shock, C.C., Ishida, J.K., Eldredge, E.P. & Seddigh, M. 2000a Yield of yellow onion cultivars in eastern Oregon and southwestern Idaho HortTechnology 10 613 620 https://doi.org/10.21273/horttech.10.3.613

    • Search Google Scholar
    • Export Citation
  • Shock, C.C., Feibert, E.B.G. & Saunders, L.D. 2000b Irrigation criteria for drip-irrigated onions HortScience 35 63 66 https://doi.org/10.21273/hortsci.35.1.63

    • Search Google Scholar
    • Export Citation
  • Shock, C.C., Feibert, E.B.G. & Saunders, L.D. 2004 Plant population and nitrogen fertilization for subsurface drip-irrigated onion HortScience 39 1722 1727 https://doi.org/10.21273/hortsci.39.7.1722

    • Search Google Scholar
    • Export Citation
  • Shock, C.C., Feibert, E.B.G. & Saunders, L.D. 2005 Single-centered and super colossal bulbs from yellow onion cultivars HortTechnology 15 399 408 https://doi.org/10.21273/horttech.15.2.0399

    • Search Google Scholar
    • Export Citation
  • Shock, C.C., Feibert, E., Jensen, L., Mohan, S.K. & Saunders, L.D. 2008 Onion variety response to Iris yellow spot virus HortTechnology 18 539 544 https://doi.org/10.21273/horttech.18.3.539

    • Search Google Scholar
    • Export Citation
  • Shock, C.C., Feibert, E., Saunders, L.D., Jensen, L., Mohan, S.K., Sampangi, R. & Pappu, H. 2011 Management of onion cultural practices to control the expression of Iris yellow spot virus Oregon State Univ., Malheur Exp. Sta. Annu. Rpt., Dept. of Crop and Soil Sci. Ext/CrS 132 23 41

    • Search Google Scholar
    • Export Citation
  • Stieber, T.D., Shock, C.C., Feibert, E., Thornton, M., Brown, B., Cook, W., Seyedbagheri, Mir-M. & Westerman, D.T. 1995 Nitrogen mineralization in Treasure Valley soils. 1993 and 1994 results Oregon State Univ., Malheur Expt. Sta. Spec. Rpt. 947 194 207

    • Search Google Scholar
    • Export Citation
  • Sullivan, D.M., Brown, B.D., Shock, C.C., Horneck, D.A., Stevens, R.G., Pelter, G.Q. & Feibert, E.B.G. 2001 Nutrient management for sweet Spanish onions in the Pacific Northwest Pacific Northwest Ext. Publ. PNW 546 1 26

    • Search Google Scholar
    • Export Citation
  • Wall, M.M., Mohammad, A. & Corgan, J.N. 1996 Heritability estimates and response to selection to the pungency and single center traits in onion Euphytica 87 133 139 https://doi.org/10.1007/bf00021886

    • Search Google Scholar
    • Export Citation
  • Wohleb, C.H. & Waters, T.D. 2016 Yield, quality, and storage characteristics of onion cultivars in the Columbia Basin of Washington in 2012–14 HortTechnology 26 230 243 https://doi.org/10.21273/horttech.26.2.230

    • Search Google Scholar
    • Export Citation
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