Potato Variety Trials 2006

Clinton Shock, Eric Eldredge, and Lamont Saunders

Malheur Experiment Station

Oregon State University

Ontario, OR

Introduction

New potato varieties were evaluated for their productivity and suitability for precessing. Potatoes are grown under contract in Malheur County 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 needs to 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.

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 10 years. A soil test taken on September 12, 2005 showed 24 lb N/acre in the top foot of soil, and 14 ppm P₂O₅, 362 ppm K₂O, 11 ppm SO₄, 2,072 ppm Ca, 473 ppm Mg, 2.5 ppm Zn, 6 ppm Fe, 4 ppm Mn, 0.4 ppm Cu, 0.5 ppm B, organic matter 0.92 percent, and pH 7.8. Fertilizer was applied in the fall to supply 200 lb P₂O₅ /acre, 200 lb S/acre, 4 lb Mg/acre, 2 lb Cu/acre, and 1 lb B/acre. The soil was fumigated in the fall with Telone II^® at 25 gal/acre. On April 12 the field was sprayed with Roundup^® at 4 pt/acre, and on April 26 the field was bedded on 36-inch row spacing.

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 Trial where Ranger Russet was used as the marker.

The Western Regional Late Harvest Trial was planted on April 27, 2006. The Statewide Trial, the Specialty Trial, and the Oregon Preliminary Yield Trial were planted on April 28. The Oregon Preliminary Yield Trial and the Specialty Trial plots were 20 seed pieces long with 2 replicates, and the Statewide and Western Regional Late Harvest Trials each had plots 30 seed pieces long with 4 replicates.

After planting, hills were reformed 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 10 and were incorporated with the Lilliston. Matrix^® herbicide was applied on May 19 and incorporated with 0.375 inch sprinkler irrigation on May 25.

Irrigation was applied 21 times (Fig. 1), from June 7 to September 13, with scheduling based on 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 potential at seed piece depth every 8 hours (Fig. 1). Irrigations were managed to prevent the soil at the seed piece depth from drying beyond 50 kPa water tension until late in the growing season. 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^® plus 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 were 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 ( J.R. Simplot Co.) at 4 lb/acre plus liquid sulfur at 6 lb S/acre was applied to remedy a nutrient deficiency and to prevent 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 and 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 means separation at the 95 percent confidence level.

Results and Discussion

Potato planting at the Malheur Experiment Station in 2006 was delayed by about 1 week by wet spring weather, with 3.57 inch rain in March and 1.76 inch rain in April. No rain was measured in July, and only 0.08 inch in August. In the 145 days between planting and vine destruction there were 81 days with high temperatures of 86°F or above, and 12 days of 100°F or above, with the maximum of 106°F on July 23. No disease, insect, or mite problems were observed in the field.

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

Among the highest total yields in the Western Regional Late Harvest Trial were produced by 'MWTX2609-4Ru', with 874 cwt/acre, 'MWTX2609-2Ru', with 845 cwt/acre, and 'CO95172-3Ru' with 803 cwt/acre (Table 1). Those three clones also produced among the highest marketable yield, however, their average fry color as measured by light reflectance was too dark for processing into frozen potato products. The clones MWTX2609-4Ru, and MWTX2609-2Ru also produced 2.5 percent sugar ends in this trial, so they may be unsuitable for processing. The clones 'AO96164-1' and 'AOA95155-7' produced 661 cwt/acre marketable yield, with light fry color, zero percent sugar ends, and high specific gravity. Russet Burbank and 'AO96141-3' produced significantly more U.S. No. 2 tubers than other clones in this trial.

Oregon Statewide Trial

In the Oregon Statewide Trial, the six clones marked with an asterisk were retained by the variety selection committee (Table 2). The clone 'AO96160-3' will graduate from the variety selection program to be released as a named variety. The clone 'AO96141-3' will advance to the Western Regional Trial, and the clones 'AO96305-3' and 'AO96365-2' will advance to the Tri-State Trial. The clones 'AO98282-5', and, 'AO00057-2' will be maintained in the Statewide Trial in 2007.

At this location in 2006, 'AO98104-1', 'AO00024-7', 'AO96364-2', and, AO98282-5 produced among the highest total yields. Russet Burbank and Shepody, two check varieties in this trial, produced significantly more U.S. No. 2 tubers, and significantly more culls than the other entries. The clones 'AO98104-1' and 'AO01012-4' produced significantly more small tubers under 4 oz than other clones in this trial. The clones AO96141-3, 'AO00076-4', 'AO99192-2', Ranger Russet, and AO98282-5 had specific gravity, a measure of tuber solids, among the highest in this trial. The clones AO96160-3, AO96141-3, 'AO96164-1', and AO98282-5 had among the lightest fry color for processing. Russet Burbank produced 25 percent sugar ends, significantly more than any other entry in this trial.

Oregon Preliminary Yield Trial

In the Preliminary Yield Trial, 140 numbered clones were compared to Russet Burbank, Ranger Russet, Shepody, and 'Russet Norkotah' (Table 3). The clones 'AO98281-2', 'OR03050-1', 'AO02045-2', and 'AO02126-3' produced among the highest total yield in this trial but were discarded due to undesirable characteristics.

The Oregon potato variety selection committee kept 12 clones, based on their performance at Hermiston, Klamath Falls, Powell Butte, and Ontario, to advance to the Statewide Trial for 2007. The clones that were advanced were: 'AO98259-5', 'AO98286-4', 'AO01057-5', 'AO02019-2', 'AO02019-3', 'AO02019-8', 'AO02027-6', 'AO02103-1', 'AO02182-1', 'AO02183-2', 'AO02196-5', and 'OR03029-2'. These clones yielded well across the four locations (Hermiston, Klamath Falls, and Powell Butte data are not shown in this report), had a low incidence of undesirable characteristics, had high percent U.S. No. 1 grade tubers, and had high specific gravity, light fry color, and resistance to developing sugar ends in response to stress.

Specialty Potato Trial

This was the second year for a colored-flesh potato variety trial at Malheur Experiment Station. Potato tubers with red to yellow carotinoid or red, blue, and purple anthocyanin pigments are of interest because of the antioxidant properties of those pigments in human nutrition. The performance of the colored clones evaluated at this location is shown in Table 4.The clones 'PA96RR1-193', 'POR00PG4-1', 'POR02PG26-5', and 'POR02PG37-2' will advance to the Regional Specialty Trial, while the clones 'POR01PG45-5', 'OR00068-11', 'POR02PG5-1', 'POR03PG12-2', 'POR03PG23-1' and 'POR03PG80-2' will be retained in the Statewide Specialty Trial for 2007.

The clones 'POR02PG2-4' with 1,029 cwt/acre, 'POR02PG26-6' with 941 cwt/acre, and POR02PG5-1with 932 cwt/acre had the highest yields of the 25 clones, far higher than the check varieties 'Yukon Gold' with 467 cwt/acre and 'All Blue' with 532 cwt/acre. Pigmentation of these specialty potatoes is highly variable. The clone POR02PG2-4 produced tubers that were reddish-purple with a red interior flesh. The clone POR02PG26-6 produced round tubers with a yellow skin with pink eyes and creamy yellow flesh. The clone POR02PG5-1 produced yellow tubers with pink eyes with a light yellow flesh. The clones POR02PG2-4, and POR02PG26-6 had a good size distribution for fresh market, but also had tubers that adhered to the stolons, and were sprouting at harvest. The clone POR02PG5-1 produced 299 cwt/acre of oversized tubers, over 10 oz, which are considered cull tubers in the usual markets for specialty potatoes.

Figure 1. Soil water potential in the sprinkler-irrigated potato variety trials at Malheur Experiment Station, Oregon State University, Ontario, OR, 2006.

Figure 2. Crop evapotranspiration (ET_c) and sprinkler irrigation applied (plus rain) to potato variety trials, Malheur Experiment Station, Oregon State University, Ontario, OR, 2006.

Table 1. Western Regional Late Harvest Trial potato yield, grade, and processing quality. Malheur Experiment Station, Oregon State University, Ontario, OR 2006.