POTATO VARIETY TRIALS 2007

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

Malheur Experiment Station

Oregon State University

Ontario, OR

 

Introduction

New potato varieties were evaluated for their productivity and suitability for processing. Potatoes in Malheur County are grown under contract for processors to make frozen potato products for the food service industry and grocery chain stores. There is very little production for fresh pack or open market, and very few growers store potatoes on their farms. There is also no production of varieties for making potato chips.

The varieties grown for processing in Malheur County, Oregon, are mainly 'Ranger Russet', 'Shepody', and 'Russet Burbank'. Harvest begins in July, providing potatoes to processing plants directly from the field. Yield of harvests later than mid-August may be limited by the "early die" syndrome, which causes early senescence of the vines of susceptible varieties, especially Shepody and Russet Burbank. Early die is caused by a complex of soil pathogens, including bacteria, nematodes, and fungi, particularly Verticillium wilt. Early die is worse when the rotation between potato crops is shorter.

Small acreages of new varieties or advanced selections are sometimes grown under contract to study the feasibility of expanding their use. To displace an existing processing variety, a new potato variety must have several outstanding characteristics. The yield should be at least as high as the yield of the currently contracted varieties. The tubers need to have low reducing sugars for light 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 and grow rapidly for early harvest. Late harvest varieties should be resistant to early die to continue bulking tubers until harvest.

Potato variety development trials at the Malheur Experiment Station in 2007 included the Western Regional Late Harvest Trial with 19 entries, the Oregon Statewide Trial with 19 entries, the Western Regional Specialty Trial of 24 colored skin and/or flesh potato varieties, and the Oregon Specialty Trial of 11 colored skin and/or flesh potato varieties. Through these trials and active cooperation with other scientists in Idaho, Oregon, and Washington, promising new lines are bred and evaluated. Eventually, the best of them may be released as new varieties.

Materials and Methods

The potato variety trials were grown using sprinkler irrigation on Greenleaf silt loam, where winter wheat was the previous crop and potato had not been grown for the past 11 years. A soil test taken on September 18, 2006 showed 160 lb nitrogen (N)/acre in the top 2 ft of soil, and 11 ppm phosphate (P₂O₅), 388 ppm potash (K₂O), 8 ppm sulfate (SO₄), 2763 ppm calcium (Ca), 407 ppm magnesium (Mg), 1.7 ppm zinc (Zn), 7 ppm iron (Fe), 3 ppm manganese (Mn), 0.7 ppm copper (Cu), 0.4 ppm boron (B), organic matter 1.7 percent, and pH 7.7. Fertilizer was applied in the fall to supply 172 lb P₂O₅ /acre, 200 lb sulfur (S)/acre, 4 lb Mg/acre, and 2 lb B/acre. The soil was fumigated in the fall with Telone^® II at 25 gal/acre and was bedded on 36-inch row spacing.

On April 19, 2007, the field was sprayed with Roundup^® at 4 pt/acre. Seed of all varieties was hand cut into 2-oz seed pieces and treated with Tops-MZ^® plus Gaucho^® dust and placed in storage to suberize. Potato seed pieces were planted in single row plots using a two-row assist-feed planter with 9-inch seed spacing in 36-inch rows. Red potatoes were planted at the end of each plot as markers to separate the potato plots at harvest, except in the specialty trials where russet was used as the marker.

The Western Regional Late Harvest, Oregon Statewide Trial, the Oregon Specialty Trial, and the Western Regional Specialty Trial were planted on April 26, 2007. Each trial had plots that were 30 seed pieces long with 4 replicates.

After planting, hills were re-formed over the rows with a Lilliston rolling cultivator. Prowl^® at 1 lb ai/acre plus Dual^® at 2 lb ai/acre were applied as a tank mix for weed control on May 8 and were incorporated with the Lilliston. Matrix^® at 1.5 oz/acre plus Eptam^® at 6 pt/acre were applied on May 29 through the sprinkler system and incorporated with 0.84-inch sprinkler irrigation.

Irrigation was applied 22 times (Fig. 1), from May 29 to September 10, with scheduling based on seven Watermark soil moisture sensors Model 200SS connected to an Irrometer Monitor (Irrometer Co. Inc., Riverside, CA) and six Watermark granular matrix sensors (Irrometer Co., Riverside, CA) connected to an AM400 data logger (M.K. Hansen Co., Wenatchee, WA) that recorded soil water tension at seed piece depth (Fig. 1). Irrigations were managed to prevent the soil at the seed piece depth from drying beyond 60 cb soil water tension. Crop evapotranspiration (ET_c) was estimated by the U.S. Bureau of Reclamation using data from an AgriMet weather station on the Malheur Experiment Station (Fig. 2). Irrigation water applied was measured using an inline flow meter (McCrometer, Hemet, CA).

Fungicide applications for control of early blight and prevention of late blight infection started with an aerial application of Ridomil Gold^® and Bravo^® at 2 lb/acre on June 18. On July 1, Topsin^® fungicide at 20 oz product/acre plus Dithane^® at 2 lb product/acre was applied. Tanos^® at 8 oz product/acre was applied on July 28, and on August 7 ammonium polyphosphate 10-34-0 at 0.18 gal/acre plus Folo Spray 20-20-20 at 4 lb/acre plus liquid sulfur at 6 lb S/acre was applied to remedy a nutrient deficiency and to prevent a two-spotted spider mite infestation.

Petiole tests were taken every 2 weeks from June 17 and fertilizer was injected into the sprinkler system during irrigation to supply the crop nutrient needs. A total of 185 lb N/acre, 1.5 lb P₂O₅/acre, 1 lb K₂O/acre, 6 lb S/acre, 0.45 lb Zn/acre, 4.2 lb Mn/acre, 2.2 lb Cu/acre, 0.4 lb Fe/acre, and 1.08 lb B/acre were applied through the sprinkler lines and aerial applications.

The vines were flailed on September 18. The vines of most entries were still green. Potatoes in the Specialty Trial were dug on October 2, the Oregon Preliminary Yield Trial on October 3-4, the Statewide Trial on October 4, and the Western Regional Late Harvest Trial was dug on October 5. At each harvest, the potatoes in each plot were lifted 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 taken of tuber defects such as growth cracks, knobs, curved or irregularly shaped tubers, pointed ends, stem-end decay, attached stolons, heat sprouts and chain tubers, folded bud ends, rough skin due to excessive russetting, pigmented eyes, or any other defect. A note was made for each plot to keep or discard the clone based on the overall appearance of the tubers.

Tubers were placed into burlap sacks and hauled to a barn where they were kept under tarps until grading. Tubers were graded by market class (U.S. No. 1 and U.S. No. 2) and weight (<4 oz, 4-6 oz, 6-12 oz, and >12 oz). Tubers were graded as U.S. No. 2 if any of the following conditions occurred: growth cracks, bottleneck shape, abnormally curved shape, or two or more knobs. A 20-tuber sample from each plot was placed into storage. The storage temperature was gradually reduced to 45°F. After 6 weeks, a 20-tuber sample from each plot (except the Specialty Trial) was evaluated for tuber quality traits for processing. Specific gravity was measured using the weight-in-air, weight-in-water method. Ten tubers per plot were cut lengthwise and the 10 center slices 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 Photovolt Reflectance Meter model 577 (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.

Data from all trials were analyzed with the General Linear Models analysis of variance procedure in NCSS (Number Cruncher Statistical Systems, Kaysville, UT) using Fisher's protected LSD (least significant difference) for means separation at the 95 percent confidence level.

Results and Discussion

Soil water potential at the seedpiece depth was allowed to become drier at the end of the growing season, after the vines died on the early maturing entries, by applying frequent sprinkler irrigations of short duration, as shown in Figure 1. This was necessary to avoid swollen lenticels and the associated possibility of rotting tubers of entries maturing early or susceptible to the early die disease syndrome, while continuing to supply a portion of the ET_c requirement for entries maturing late or resistant to early die.

Precipitation for May 25 through September 17 was 0.80 inch, the potato crop evapotranspiration (ET_c) for the late-harvest trials totaled 29.26 inch, and the trials received 28.45 inch of irrigation plus precipitation (Fig. 2). The incremental increases in the irrigation plus rainfall curve show the 21 sprinkler irrigations applied during the growing season.

Western Regional Late Harvest Trial

The clones with the highest total yields in the Western Regional Late Harvest Trial were 'AO96164-1', with 827 cwt/acre, 'AO96141-3', with 822.8 cwt/acre, and Russet Burbank with 763.8 cwt/acre (Table 1). The clones AO96164-1, 'A97287-6', and 'CO95172-3RU' had among the highest U.S. No. 1 yields. Clone AO96164-1 produced 777.3 cwt/acre marketable yield, 51.7 fry color light reflectance, zero percent sugar ends, and 1.0883 specific gravity. Russet Burbank and AO96141-3 produced significantly more U.S. No. 2 tubers than other clones in this trial.

Oregon Statewide Trial

At this location in 2007, AO96164-1, AO96141-3, Russet Burbank, and CO95172-3RU were among the clones with the highest total yields. The clones AO96164-1, A97287-6, and CO95172-3RU were among the clones with the highest yields of U.S. No. 1 tubers. The clones AO96141-3, Ranger Russet, 'A95409-1', and AO96164-1 had specific gravity, a measure of tuber solids, among the highest in this trial. The clones 'AO96052-1RU', AO96164-1, 'AO95154-1', and 'AOTX95265-2ARu', had among the lightest fry color for processing (Table 2).

Colored Flesh Potato Trials

This was the second year of testing colored flesh potato varieties at the Malheur Experiment Station. Potato tubers with red to yellow carotinoid or red, blue, and purple anthocyanin pigments are of interest because of the anti-oxidant properties of those pigments in human nutrition. Two trials tested specialty potato varieties in 2007: Western Region Specialty and Oregon Specialty.

Western Region Specialty Trial

In the Western Region Specialty Trial, 'POR02PG5-1', 'AC97521-1R/Y', 'A96510-4Y', and 'ATTX98500-2P/Y' were among the clones with the highest total yield (Table 3). Clones AC97521-1R/Y, ATTX98500-2P/Y, POR02PG5-1, and 'POR01PG20-12' had among the highest yield of 4- to 10-oz tubers. 'Dark Red Norland', 'Red LaSoda', 'ATTX961014-1R/Y', ATTX98500-2P/Y, POR02PG5-1, 'Yukon Gold', A96510-4Y, and 'POR02PG26-5' had more than 100 cwt/acre of oversized tubers over 10 oz, which are considered cull tubers in the usual markets for specialty potatoes. Clones varied greatly in appearance and taste (Tables 5 and 6).

Oregon Advanced Specialty Potato Trial

The clone 'OR00068-11' with 848.3 cwt/acre, had the highest total yield, followed by 'POR04PG03-9' with 726.8 cwt/acre, and 'POR04PG01-2' with 714.9 cwt/acre, far higher than the check varieties Yukon Gold with 465.3 cwt/acre and 'All Blue' with 566.2 cwt/acre (Table 4). Yukon Gold, 'POR03PG80-2', and 'POR04PG39-2' had more than 100 cwt/acre of oversized tubers over 10 oz. Promising clones with favorable yield, appearance, and taste (Tables 7 and 8) are being advanced to the Western Regional Specialty Trial.

Figure 1. Soil water potential in the sprinkler-irrigated potato variety trials at Malheur Experiment Station, Oregon State University, Ontario, OR, 2007.

Figure 2. Crop evapotranspiration (ET_c) and sprinkler-irrigation applied (plus rain) to potato variety trials, Malheur Experiment Station, Oregon State University, Ontario, OR, 2007.