Potato Variety Trials 2002

Eric P. Eldredge, Clinton C. Shock, and Lamont D. Saunders

Malheur Experiment Station

Oregon State University

Ontario, OR

Introduction

Malheur County produced 8,600 acres of potatoes in 2002, with an average yield of 371 cwt/acre. Potatoes are grown under contract with potato processors for frozen products for the food service industry. There is very little production for fresh pack or open market, and growers do not have storages on their farms. There is also no production of varieties for making potato chips. There is no potato seed production in Malheur County because high populations of aphids result in virus infection in the tubers. The varieties grown are mainly 'Shepody' for early harvest and 'Ranger Russet' and 'Russet Burbank' for late harvest. Harvest begins in July, providing potatoes to processing plants directly from the field.

Small acreages of some new varieties are contracted by processors each year to study the feasibility of expanding the use of the new varieties. To displace an existing processing variety, a new potato variety needs to have several outstanding characteristics. The yield should be at least as high as the yield of 'Russet Burbank'. The percentage of U.S. No. 1 tubers must be high, and the tubers need to have low reducing sugars for light, uniform fry color and high specific gravity. A new variety should be resistant to tuber defects or deformities caused by disease, water stress, or heat. It should begin tuber bulking early if it is a variety for early harvest. Or, if it is a late-harvest variety, it should be resistant to early vine death, known as the "early die" syndrome, and continue tuber development late in the growing season. Early die is caused by a disease complex of common soil fungi, including Verticillium and Colletotrichum.

Potato variety development trials at Malheur Experiment Station in 2002 included an 8-Hill trial of 14 long russet clones from the USDA Agricultural Research Service (ARS) potato breeding program at Aberdeen, Idaho; the Oregon Preliminary Yield Trial with 81 entries; the Oregon Statewide Trial with 22 entries; the Western Regional Early-harvest Trial with 16 entries; and the Western Regional Late-harvest Trial with 16 entries.

Materials and Methods

Five potato variety trials were grown under sprinkler irrigation on Owyhee silt loam, where winter wheat was the previous crop. The wheat stubble was flailed and the field was irrigated and disked. A soil test taken October 1, 2001 showed 40 lb N/acre, 90 lb P/acre, 750 lb K/acre, organic matter 1.8 percent, and pH 8.1. Fall fertilizer included 50 lb N/acre, 160 lb P₂O₅/acre, 178 lb K₂O/acre, 40 lb SO₄/acre, 190 lb S/acre, 10 lb Zn/acre, 4 lb Mn/acre, 2 lb Cu/acre, and 1 lb B/acre. The field was ripped, Telone II was injected at 22 gal/acre, and the field was bedded on 36-inch row spacing. A soil test taken on March 4, 2002 showed available nitrate plus ammonia was 93 lb N/acre in the top 2 ft of soil.

Seed of all varieties was hand cut into 2-oz seed pieces and treated with Tops-MZ+ Gaucho dust 1-2 weeks before planting and placed in storage to suberize. The Western Regional Early-harvest Trial was planted April 16, 2002, and the other trials were planted April 19. The 8-Hill trial was unreplicated, the Preliminary Yield Trial had two replicates, and the Statewide, Western Regional Early-harvest, and Western Regional Late-harvest Trials each had four replicates. Plots were planted using a two-row cup planter with seed spaced 9 inches in the row, with rows 36 inches apart. After planting, hills were formed over the rows with a Lilliston rolling cultivator. Prowl at 1 lb ai/acre plus Dual at 2 lb ai/acre, in 30-gal/acre spray mix, was applied and incorporated with the Lilliston on April 29. Matrix herbicide was applied at 1.25 oz/acre on May 16.

Fungicide applications to help control early blight and prevent late blight infection started with an aerial application of Ridomil Gold and Bravo at 1.5 pint/acre on June 4, followed with Dithane at 4 pint/acre on June 16. Bravo Weatherstik plus Super-six flowable sulfur plus 0.1 lb boron/acre was applied on July 3. Powdered sulfur was applied at 30 lb/acre by airplane on July 23 to control mites and powdery mildew.

Petiole tests were taken every 2 weeks from June 7 to August 2. Fertilizer was injected into the sprinkler line during irrigation on June 14 to supply 16 lb N/acre, 0.2 lb Mg/acre, 0.16 lb Mn/acre, and 9 lb SO₄/acre; on June 25 to supply 16 lb N/acre, 0.2 lb Mn/acre, and 0.4 lb Fe/acre; on July 5 to supply 23 lb N/acre, 0.25 lb Zn/acre, 0.25 lb Mn/acre, and 0.2 lb Cu/acre; on July 12 to supply 17 lb N/acre, 0.21 lb Zn/acre, 0.21 lb Mn/acre, and 0.17 lb Cu/acre; on July 26 to supply 20 lb N/acre, 10 lb S/acre, 3 lb Mg/acre, 0.2 lb Zn/acre, 0.2 lb Mn/acre, 0.2 lb Cu/acre, and 0.1 lb B/acre; and on August 12 (late trials only) to supply 20 lb N/acre, 0.25 lb Zn/acre, 0.25 lb Mn/acre, and 0.2 lb B/acre.

The sprinkler system was operated 13 times, from May 22 to August 26, with scheduling based on soil water potential measured with six Watermark soil moisture sensors (Irrometer Co. Inc., Riverside, CA) logged every 8 hours by a Hansen AM400 (MK Hansen Co., East Wenatchee, Wa). The AM400 unit was read daily through the summer to predict crop water needs, and an irrigation was applied when the average soil moisture in the potato root zone at the seed piece depth reached -70 kPa. Water applied was measured by recording the sprinkler set duration. Potato evapotranspiration (ET_c) was measured using a U.S. Bureau of Reclamation Agrimet station at the Malheur Experiment Station.

Vines were flailed in the early harvest trial on August 14, and in the late harvest trials on September 10. The vines of most varieties had died by the date of the last irrigation on August 26. Western Regional Early-harvest Trial potatoes were lifted August 21 with a two-row digger that laid the tubers back onto the soil in each row. Visual evaluations included observations of desirable traits, such as a high yield of large, smooth, uniformly shaped and sized, oblong to long, attractively russetted tubers, with shallow eyes evenly distributed over the tuber length. Notes were also made of tuber defects such as growth cracks, knobs, curved or irregularly shaped tubers, pointed ends, stem-end decay, stolons that remained attached, folded bud ends, rough skin due to excessive russetting, pigmented eyes, or any other defect, and a note to keep or discard the clone based on tuber appearance.

Tubers were placed into burlap sacks and hauled to a barn where they were kept under tarps until grading. After grading, a 20-tuber sample from each plot in the Western Regional Early-harvest Trial was evaluated for tuber quality traits for processing. Specific gravity was measured using the weight-in-air, weight-in-water method, and 10 tubers per plot were cut lengthwise and examined for internal defects. Center slices from 10 tubers were fried for 3.5 min in 375°F soybean oil. Percent light reflectance was measured on the stem and bud ends of each slice using a model 577 Photovolt Reflectance Meter (Seradyn, Inc., Indianapolis, IN) with a green tristimulus filter, calibrated to read 0 percent light reflectance on the black standard cup and 73.6 percent light reflectance on the white porcelain standard plate.

The potatoes in the Preliminary Yield Trial were dug on September 16, and the potatoes in the Western Regional Late-harvest, Statewide, and 8-Hill Trials were dug on September 17 and 18. At harvest, the potatoes in each plot were visually evaluated. Tubers were graded and a 20-tuber sample from each plot was placed into storage. The storage was kept near 90 percent relative humidity and the temperature was gradually reduced to 45°F. Tubers were removed from storage November 15 through December 3 and evaluated for tuber quality traits, specific gravity, and fry color as described above.

Results and Discussion

Dry weather prevented late blight from developing in 2002. No powdery mildew or mite problems were observed in the field. Precipitation for April through August was 1.7 inches. The crop ET_c for the early-harvest trial totaled 22.61 inches, and the trial received 23.5 inches of irrigation plus precipitation, or 104 percent of ET_c. For the late-harvest trials ET_c totaled 23.53 inches, and the trials received 24.21 inches of irrigation plus precipitation, or 103 percent of ET_c (Fig. 1). These trials should have been irrigated when soil water potential approached -60 kPa, rather than the -70 kPa criterion (Fig. 2). Irrigations would have been about a day earlier, and would have resulted in more irrigations during the season.

At the Malheur Experiment Station, spring weather in 2002 was cool and dry, followed by near record heat in early July. The temperature on July 10 was 102^o F, followed by 107^o, 106^o, 107^o, 98^o, 97^o, 96^o, and 102^o on subsequent days. Overnight low temperatures from July 10 to 25 exceeded 60^o F, and averaged 67.3^o F, with the highest overnight low, 75^o F, on July 12-13. The extreme heat stressed the potato plants, causing reduced yields and early senescence. The below-average yields of these trials may be attributable to the heat in July (Tables 1-5). Yields of other crops, such as wheat and sugar beet, were also below average in Malheur County in 2002.

8-Hill Trial

Eight hills were grown of each of 14 clones selected for long, russeted tubers from the Aberdeen ARS potato breeding program. The 14 clones were evaluated for tuber type, yield, grade, and processing quality (Table 1). Several of the clones had high yields, produced a high percentage of U.S. No. 1 tubers, or had good processing quality. The clone 'NDA7848-2' yielded a total of 772 cwt/acre, with 83 percent U.S. No. 1 grade tubers, and specific gravity of 1.079 g/cm³, but the average fry strip light reflectance of 28.8 percent was too dark for acceptable processing. The clone 'A98323-8' yielded 762 cwt/acre total, with 81 percent U.S. No. 1 grade, specific gravity 1.0855, and fry strip light reflectance of 53.1 percent. The clone 'A98345-1' yielded 748 cwt/acre total, with 88 percent U.S. No. 1 grade, specific gravity 1.1022, fry strip light reflectance of 48.7 percent, and, at harvest, was evaluated as one to keep.

Preliminary Yield Trial

In the Preliminary Yield Trial, 76 numbered clones were compared to 'Russet Burbank', 'Ranger Russet', 'Shepody', 'Norkotah', and 'Umatilla Russet' (Table 2). The Oregon potato variety selection committee kept 16 clones to advance to the Statewide Trial for 2003. The clones that were kept, 'AO95250-4', 'AO95250-5', 'AO96128-10', 'AO96141-3', 'AO96148-1', 'AO96201-1', 'AO96205-3', 'AO96212-3', 'AO96212-6', 'AO96213-3', 'AO96240-5', 'AO96241-3', 'AO96249-16', 'AO96261-2', 'AO98133-2', and 'AO98133-4', are marked with an asterisk in the entry list. These clones yielded well across the four locations (Hermiston, Klamath Falls, Ontario, and Powell Butte), had a high percent of U.S. No. 1 grade tubers, had high specific gravity and light fry color needed for processing, and low incidence of undesirable characteristics.

Oregon Statewide Trial

In the Oregon Statewide Trial, seven clones were retained by the variety selection committee. Four clones; 'AO96177-6', 'AO97133-2', 'AO97143-1' and 'AO97175-13' will be maintained in the Statewide Trial in 2003 (Table 3). Three other clones were advanced, 'AO94110-203', to the Western Regional Trials for 2003 and 'AO96160-3', 'AO96164-1' will advance to the Tri-State Trial. At this location in 2002, 'AO97303-2' produced a total yield of 651 cwt/acre, with 90 percent U.S. No. 1 grade, good specific gravity of 1.091 g/cm³, and an average fry strip light reflectance of 42.8 percent. 'AO97143-1' produced total yield of 640 cwt/acre, with 78 percent U.S. No. 1, specific gravity of 1.097 g/cm³, and fry strip light reflectance of 50.0 percent. 'AO97178-1' produced total yield of 568 cwt/acre, with 90 percent U.S. No. 1, specific gravity of 1.102 g/cm³, and fry strip light reflectance of 42.6 percent. 'AO94110-203' produced total yield of 539 cwt/acre, with 82 percent U.S. No. 1, specific gravity of 1.098 g/cm³, and fry strip light reflectance of 47.5 percent. 'Russet Burbank' had 70 percent sugar ends, far more than any other variety.

Western Regional Early-harvest Trial

In the Western Regional Early-harvest Trial, 'A9305-10' with 489 cwt/acre total yield, 'Russet Burbank' with 484 cwt/acre, 'A9045-7' with 470 cwt/acre, and 'Shepody' with 463 cwt/acre were among the highest in total yields (Table 4). All of those clones except 'Russet Burbank' had acceptable specific gravity and fry color. In production of marketable tubers (the total of U.S. No.1 plus U.S. No. 2 grades), 'A9305-10' with 423 cwt/acre, 'A9045-7' with 414 cwt/acre, 'A9304-3' with 404 cwt/acre, and 'ATX9202-1Ru' with 363 cwt/acre were among the highest. 'Shepody' produced 169 cwt/acre cull tubers, significantly more culls than any other variety in this trial.

Western Regional Late-harvest Trial

In the Western Regional Late-harvest Trial, among the highest for total yield were 'Ranger Russet' with 471 cwt/acre, 'A9305-10' with 460 cwt/acre, 'A9304-3' with 450 cwt/acre, 'A9045-7' with 439 cwt/acre, and 'Shepody' with 407 cwt/acre (Table 5). Among the highest for marketable yield, 'Ranger Russet' produced 456 cwt/acre marketable yield, 'A9305-10' yielded 443 cwt/acre, 'A9304-3' yielded 439 cwt/acre, and 'A9045-7' yielded 422 cwt/acre marketable yield. 'Russet Burbank' produced 166 cwt/acre U.S. No. 2 tubers, which was significantly more than any other variety in this trial, and 'Shepody' produced 100 cwt/acre U.S. No. 2, significantly more than the other varieties except 'Russet Burbank'.

Figure 1. Evapotranspiration and sprinkler irrigation applied (plus rain) to potato variety trials, Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.

Figure 2. Soil water potential recorded by Hansen AM400 in potato variety trials, Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.Table 1. Yield, grade, and processing quality of 14 early selections in an unreplicated 8-Hill Trial, Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.