Wisconsin Potato Variety and Advanced Selection Evaluation Trial 

2005

Materials and Methods

Yield and Tuber Quality Studies

Seed Cutting: Potato seed of each of the varieties studied was obtained from cooperators in other states during late March and early April, 2005.  Approximately one week prior to the scheduled planting date at each trial site seed tubers were cut by hand into 1 1/2 - 2 oz. seed pieces when possible.  Seed size and amount was variable forcing the use of whole or cut seed <1 1/2 oz. at times.  Twenty seed pieces were cut for each replicate, placed in mesh bags and held in storage to suberize. 

Planting, Maintenance and Harvest: Furrows were opened at each trial site using a mechanical potato planter with the covering disks removed.  Fertilizer impregnated with systemic insecticide was laid down during the furrow opening process.  Seed pieces were spaced evenly in the furrow using a hand planter designed and built by the author.  Red, white, yellow flesh and specialty varieties were spaced 12 in. apart, and russet varieties were spaced 16 in. apart.  Plots consisted of 20 seed pieces planted in a single row with 5 tubers of contrasting type separating the plots.  This resulted in solid rows of potatoes with no end effect to compromise yield data and tuber quality evaluation.  Replicates were randomly distributed within rows in the field.  Three replicates were planted at Hancock and two at each of the other trial sites.  The crop was produced under production management schemes common in the respective areas.  Stand counts were taken twice during the growing season.  Vines were killed approximately 120 days after planting at Hancock, Antigo and Spooner, and approximately 100 days after planting at the muck site.  Tubers were harvested 2-3 weeks after vine-kill.  Plots were harvested using various types of mechanical harvesting equipment.  All plots were taken to the Hancock Agricultural Research Station for grading and further evaluation.

Post Harvest Data Collection: Plots were graded according to U. S. No. 1 standards.  Tubers <1 7/8 in. diameter and culls were sorted out and their weights recorded.  The remaining U. S. No. 1 tubers were size graded into six size categories (<4 oz., 4-6 oz., 6-10 oz., 10-13 oz., 13-16 oz. and >16 oz.) using an Exeter optical sizer.  One crate (up to 30 lbs.) of 4-13 oz. tubers were saved from each replicate for each variety.  Following grading, specific gravity was measured for each replicate using the weight in air/weight in water method.  A 10 tuber random sample was drawn from each replicate for evaluation of internal defects.  Each tuber was cut in half and one half discarded.  The remaining half was evaluated visually for brown center (precursor to hollow heart), hollow heart, internal brown spot, vascular discoloration and stem end browning. 

Processing Studies

   Sample Collection: Samples of all white and russet potato varieties included in the trial were collected for processing studies.  The samples were drawn from plots grown at the Hancock trial site following grading.  Up to one crate (30 lbs.) of 4-13 oz. tubers was collected from each replicate for each variety.  Following specific gravity measurements and evaluation of internal qualities, sub-samples we randomly collected from each of the three crates per variety and combined into one crate.  Five samples of six 6-10 oz. tubers were taken from the combined crate of each variety and placed in mesh onion bags.  Samples of each variety were divided into groups and designated for processing at 1, 2, 3, 4 and 5 month intervals after harvest.

   Storage: Samples were held at ambient air temperature for one week and then transferred to a nearby commercial potato storage for sprout-inhibiting treatment and long-term storage at 47°F.  Samples were moved to 65°F for one day prior to each processing date.

   Processing: Five tubers were selected randomly from each six-tuber sample at each processing interval.  Round white varieties were processed into chips.  Tubers were cut in half lengthwise (along stem end to bud end axis) using a potato splitter designed and built by the author.  One half of the tuber was discarded.  Two slices were taken from the remaining half of each tuber using a slicer designed and built by the author.  Slices were approximately one millimeter thick.  The first slice from each tuber half was discarded and the second was used for the processing evaluation.  Each slice was rinsed briefly in cold water to remove free starch granules and then drained on a paper towel.  The slices were placed in a specially designed wire basket to hold them flat while frying.  The slices were fried in refined soybean oil at 365°F until dehydration was complete (determined when bubbles stopped rising to the oil surface).  Slices were drained in the frying basket for a short period of time and then placed on paper towels for further draining.  Chips from each processing interval were scored visually and photographed within three hours after frying.  Long russet varieties were processed into French fries.  Tubers were cut into 3/8” x 3/8” fries using a Nemco Model N55450 restaurant-style hand-operated cutter.  The center fry was taken from each tuber and placed in a specially designed wire basket to hold them flat while frying.  All fries were oriented bud end up and maintained in this orientation throughout the processing, scoring and photographing process. The fries were fried in refined soybean oil at 375°F for 3½ minutes.  Fries were drained in the frying basket for a short period of time and then placed on paper towels for further draining.  Fries from each processing interval were scored visually and photographed within one hour after frying.

    Scoring: Processed chip samples were evaluated visually and scored on a scale of 1-10 using a color chart developed at the Rhinelander Agricultural Research Station within three hours after frying.  Scores presented in the tables are an average of the five chips in each sample.  A score of 1 represents the lightest color and 10 the darkest color.  Scores of 4 or less are considered acceptable color.  Processed French fry samples were evaluated visually and scored according to the USDA Fry Color Chart (.01, .03, .05, 1, 2, 3, 4) within one hour after frying.  A score of .01 represents the lightest color and 4 the darkest color.  Scores of 2 and less are considered acceptable.  Scores presented in the tables are an average of the five fries in each sample.