2002 Onion Variety Trials

Clinton C. Shock, Erik B. G. Feibert, and Lamont D. Saunders

Malheur Experiment Station

Oregon State University

Ontario, OR

Introduction

The objective of the trials was to evaluate yellow, white, and red onion varieties for bulb yield, quality, and single centers.

Methods

The onions were grown on an Owyhee silt loam previously planted to wheat. In the fall of 2001, the wheat stubble was shredded, and the field was disked, irrigated, ripped, moldboard-plowed, roller-harrowed, fumigated with Telone C-17 at 20 gal/acre, and bedded. Before plowing, 100 lb P₂O₅/acre, 100 lb K/acre, 50 lb Mg/acre, 10 lb Zn/acre, 3 lb Cu/acre, and 1 lb B/acre were broadcast. A soil sample taken on May 5 showed a pH of 7.5, 2.4 percent organic matter, 14 ppm nitrate-N, 12 ppm P, and 299 ppm K.

A full season trial and an early maturing trial were conducted adjacent to each other. Both trials were planted on March 22 in plots four rows wide and 27 ft long. The full season trial had 41 varieties from 10 companies and the early maturity trial had six varieties from five companies. The experimental design was a randomized complete block with five replicates. A sixth non-randomized replicate was planted for purposes of demonstrating onion variety performance to growers and seed company representatives. The onion seed was planted in double rows spaced 3 inches apart at 9 seeds per ft of single row. Each double row was planted on beds spaced 22 inches apart with a customized planter using John Deere Flexi Planter units equipped with disc openers. The onion rows received 3.7 oz of Lorsban 15G per 1,000 ft of row (0.82 lb ai/acre), and the soil surface was rolled on March 25. On May 7, alleys 4 ft wide were cut between plots, leaving plots 23 ft long. From May 8 through 10, the seedlings were hand thinned to a plant population of two plants per ft of single row (6-inch spacing between individual onion plants, or 95,000 plants/acre). The field was sidedressed with urea at 90 lb N/acre on May 15 and on June 11.

The trial was managed to avoid yield reductions from weeds, pests, and diseases. Weeds were controlled with a cultivation on April 18 and with an application of Goal at 0.12 lb ai/acre, Buctril at 0.37 lb ai/acre, Poast at 0.74 lb ai/acre, and Prowl at 1 lb ai/acre on May 31. After lay-by the field was hand weeded as necessary. Aerial applications of Poast at 0.74 lb ai/acre were made on July 31 and August 8. Thrips were controlled with four aerial applications of Warrior and Lannate (June 19, July 2, July 18, and August 6) and one aerial application of Warrior on June 10. Warrior was applied at 0.03 lb ai/acre and Lannate was applied at 0.26 lb ai/acre.

The trial was furrow irrigated when the soil water potential at 8-inch depth reached -20 kPa (Fig. 1). Soil water potential was monitored by six granular matrix sensors (GMS, Watermark Soil Moisture Sensors Model 200SS, Irrometer Co., Riverside, CA) installed in mid-June below the onion row at 8-inch depth. Sensors were automatically read three times a day with an AM-400 meter (Mike Hansen Co., East Wenatchee, WA). The last irrigation was on August 27.

Onions from the middle two rows in each plot in the early maturity trial were lifted, topped by hand and bagged on August 28. The onion bags were hauled to a barn on August 30. On September 5 the onions were graded. The onions in the full season trial were lifted on September 9 to field cure. Onions from the middle two rows in each plot of the full season trial were topped by hand and bagged on September 18. The bags were put in storage on September 20. The storage shed was managed to maintain an air temperature of approximately 34°F. Onions from the full season trial were graded out of storage in early January 2003.

During grading, bulbs were separated according to quality: bulbs without blemishes (No. 1s), split bulbs (No. 2s), neck rot (bulbs infected with the fungus Botrytis allii in the neck or side), plate rot (bulbs infected with the fungus Fusarium oxysporum), and black mold (bulbs infected with the fungus Aspergillus niger). The No. 1 bulbs were graded according to diameter: small (<2¼ inch), medium (2¼-3 inch), jumbo (3-4 inch), colossal (4-4¼ inch), and supercolossal (>4¼ inch). Bulb counts per 50 lb of supercolossal onions were determined for each plot of every variety by weighing and counting all supercolossal bulbs during grading.

In early September, 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 rated. The onions were cut equatorially through the bulb middle and, if multiple centered, the long axis of the inside diameter of the first single ring was measured. These multiple-centered onions were ranked according to the diameter of the first single ring: "small double" had diameters <1½ inch, "intermediate double" had diameters from 1½ to 2¼ inch, and "blowout" had diameters >2¼ inch. Single-centered onions were classed as a "bullet." Onions were considered functionally single centered for processing if they were a "bullet" or "small double."

Varietal differences were compared using ANOVA and least significant differences at the 5 percent probability level, LSD (0.05).

Results and Discussion

Varieties are listed by company in alphabetical order. The LSD (0.05) values at the bottom of each table should be considered when comparisons are made between varieties for significant differences in performance characteristics. Differences between varieties equal to or greater than the LSD (0.05) value for a characteristic should exist before any variety is considered different from any other variety in that characteristic.

Early Maturity Trial

The percentage of "bullet" single centers averaged 7.9 percent and ranged from 0 percent for 'WS228LD' to 24.8 percent for 'Varsity' (Table 1). 'Varsity' and 'SWO 4014' were among the highest in percentage of "bullet" single centers. The percentage of onions that were functionally single centered averaged 30.5 percent and ranged from 2.4 percent for 'Expression' to 70.4 percent for 'Varsity'. 'Varsity' had the highest percentage of functionally single-centered bulbs.

Total yield averaged 914 cwt/acre and ranged from 592 cwt/acre for 'WS228LD' to 1098 cwt/acre for 'Caballero' (Table 3). 'Caballero' and 'Expression' had the highest total yield. Supercolossal-size onion yield averaged 19.4 cwt/acre and ranged from 1.9 cwt/acre for 'WS228LD' to 38.8 cwt/acre for 'Caballero'. 'Caballero' and 'Expression' were among the highest yielding varieties of supercolossal bulbs. Not considering supercolossals, colossal-size onion yield averaged 200.8 cwt/acre and ranged from 8.7 cwt/acre for 'WS228LD' to 365.7 cwt/acre for 'Expression'. 'Expression' and 'Caballero' had the highest colossal bulb yields. Split-bulb yield ranged from 3.2 cwt/acre for 'WS228LD' to 396.5 cwt/acre for 'Fort Knox'. 'Fort Knox' had the highest yield of split bulbs.

Maturity on July 30 ranged from 0 percent for 'Fort Knox' to 52 percent for 'Caballero'. 'Caballero' and 'WS228LD' were the most mature on July 30.

Full Season Trial

The percentage of "bullet" single centers ranged from 0.8 percent for 'Delgado' and 'Red Rider' to 74 percent for 'SX 7000ON' (Table 2). Variety 'SX 7000ON' had the highest percentage of onions with "bullet" single centers. Varieties 'Vaquero', 'Granero', and 'SR 7002ON' were among the highest in percentage of onions with "bullet" single centers. The percentage of functionally single-centered bulbs ranged from 9.6 percent for 'Red Rider' to 92 percent for 'SX 7000ON'.

Total yield out of storage in January 2003 averaged 937.6 cwt/acre and ranged from 437.2 cwt/acre for 'Tango' to 1,217.9 cwt/acre for 'XPH97H24' (Table 4). 'XPH97H24', 'T-433', 'SWO6001', 'Sweet Perfection', 'Tequila', and 'Vaquero' were among the highest varieties in total yield. Supercolossal-size onion yield averaged 87.7 cwt/acre and ranged from 0 cwt/acre for 'T-441', 'Flamenco', and 'Tango' to 240.1 cwt/acre for 'Superstar'. 'Superstar', 'Sweet Perfection', 'Ringstar', 'Tequila', 'Harvest Moon', 'Mesquite', 'XPH97H24', 'XPH01N3', 'Santa Fe', and 'Ranchero' were among the varieties with the highest supercolossal yield. The number of bulbs per 50 lb of supercolossal onions averaged 34 and ranged from 30 for 'T433', 'T-467', 'Mesquite', and 'Supertstar' to 55 for 'Red October'. Of the yellow bulb varieties, only 'Sabroso' had supercolossal counts above the acceptable range (averaged too small because they were almost all at the small end of the size range) for marketing as supercolossal (28-36 count per 50 lb).

Not considering supercolossals, colossal-size onion yield averaged 317.1 cwt/acre and ranged from 18.6 cwt/acre for 'Flamenco' to 478.3 cwt/acre for 'SWO 6001'. 'SWO 6001', 'T-433', 'Vaquero', 'Santa Fe', 'XPH97H24', 'Ranchero', 'Superstar', 'Torero', 'Sweet Perfection', 'Ringstar', 'Mesquite', and 'XPH01N3' had colossal bulb yields greater than 450 cwt/acre.

Decomposition in storage averaged 1.1 percent and ranged from 0.1 percent for 'Ranchero' to 4.9 percent for 'SX 4391 ON'. No. 2 bulbs averaged 49.2 cwt/acre and ranged from 0.7 cwt/acre for 'SX 7000ON' to 202.6 cwt/acre for 'Red Rider'. Bolting averaged 0.2 bolted onions out of approximately 368 onions in each 4-row plot. Bolting ranged from 0 bolted onions per plot for many varieties to only 1.2 bolted onions per plot for 'XPH 01N3'.

Figure 1. Soil water potential at 8-inch depth over time for onions furrow irrigated when the soil water potential reached -20 kPa. Soil water potential is the average of six sensors. Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.

Table 1. Onion multiple-center rating for early maturing varieties. Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.

Table 2. Onion multiple-center rating. Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.