2002 Wisconsin Potato Variety and Advanced Selection Evaluation Trial

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, 2002.  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 and white 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 2 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.  Vine maturity was evaluated at the Hancock site at 120 days after planting.  Vines were killed approximately 120 days after planting and tubers were harvested 2-3 weeks after vine-kill.  Plots were harvested using various mechanical harvesting equipment.  All plots were taken to the Hancock Agricultural Research Station for grading and further evaluation.  Weather was favorable for late blight development in 2002.  However, no late blight was found in any trial plots.

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 6 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 and two red varieties included in the trial were collected for processing studies.  The samples were drawn following grading from plots grown at the Hancock trial site.  Up to one crate (30 lbs.) of 4-13 oz. tubers were collected from each replicate for each variety.  Following specific gravity measurements and evaluation of internal qualities, sub-samples were randomly collected from each of the three crates per variety and combined into one crate.  The crates were moved into a walk-in cooler for storage.  Sub-samples were drawn from each crate at various intervals and processed into chips or French fries.

Storage: Sub-sample 1 was processed into chips or French fries shortly after grading and is labeled as Direct from Field in the processing data tables that follow.  Sub-samples 2, 3 and 4 were moved from air temperature holding into 50°F storage (walk-in cooler) at the Hancock Agricultural Research Station and held for four weeks.  Sub-sample 2 was removed after four weeks, warmed at 65°F for one day and processed into chips or French fries.  Sub-sample 2 is labeled as 1 Month Direct in the data tables.  Sub-samples 3 and 4 remained in storage as the temperature was gradually lowered to 40°F over the next two weeks.  Sub-samples 3 and 4 were removed from storage after six weeks at 40°F (12 weeks total in storage). Sub-sample 3 was warmed at 65°F for one day and processed into chips or French fries.  Sub-sample 3 is labeled as 3 Months Direct.  Sub-sample 4 was held at 65°F for two weeks and processed into chips or French fries.  Sub-sample 4 is labeled as 3 Months Reconditioned.

Processing: At each processing interval five tubers, each approximately 6-10 oz. in weight, were randomly selected for processing.  Round white varieties were processed into chips.  Tubers were cut in half lengthwise (along stem end to bud end axis) using a sharp knife.  One half of the tuber was discarded.  Two slices were taken from the remaining half of each tuber using a chip slicer designed and built by the author.  Slices were approximately one millimeter thick.  The first slice from each tuber 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 that holds the chips flat while frying.  The slices were fried in Quali-Fry Liquid Frying Shortening (refined soybean oil) at 365°F until dehydration was complete (determined when bubbles stopped rising to the oil surface; generally 2-3 minutes).  Slices were drained in the frying basket for a short period of time and then placed on paper towels for further draining.  Slices from each frying event were placed in closed plastic bags and held until all frying was finished.  Long russet and two red 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 French fry cutter.  The center fry was taken from each tuber and placed in a specially-designed wire basket that holds the fries flat while frying.  The fries were fried in refined soybean oil at 375°F for 3 1/2 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 and photographed within 24 hours after processing.  Stem end vs. bud end orientation was maintained throughout the processing, scoring and photography phases.  The stem end is oriented at the bottom of each photograph.

Scoring: Processed chip samples were taken to the Rhinelander Agricultural Research Station for scoring.  Individual processed slices in each sample were evaluated visually and scored on a scale of 1-10 according to the Potato Chip International Institute (PCII) color chart.  Scores presented in the tables are an average for 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 to be acceptable color.  The chips in each sample were then crushed and mixed to give a fine, homogenous sample for evaluation with a HunterLab ColorQuest 45/0 spectrophotometer.  The crumbs were placed in a small glass dish (Pyrex petri dish 60 x 15 mm) to a depth of approximately 15 mm.  The dish was placed on the 50 mm light aperture of the spectrophotometer and color readings were taken.  The “Hunter” measures color on three scales: L = black/white; a = red/green and b = yellow/blue.  Data were collected on all three scales for each variety, but only the L scale data is presented in the tables.  References for the L scale are 100 = white and 0 = black.  Hunter scores of 60 (+/- 2.2) and above are considered acceptable.  Processed French fry samples were scored visually within 24 hours after frying using the USDA Fry Color Chart (.01, .03, .05, 1, 2, 3, 4).  A score of .01 represents the lightest color and 4 the darkest color.  Scores of 2 and less are considered acceptable.  French fries were not scored with a spectrophotometer.