Wisconsin 

Potato Variety and Advanced Selection Evaluation Trial 

2006

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, 2006.  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 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, all three replicates were dumped together in a large plastic tub.  The total amount of tubers was then divided equally into three samples with special care taken to select the tubers as randomly as possible to ensure blending of the plots.    

   Storage: The samples of each variety were stored together at 58° F for four weeks to allow for wound healing.  Following the wound healing process, the three samples of each variety were separated and moved to long-term storage at 42°F, 45°F and 48°F. 

    Scoring: Processed chip samples 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 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 slab (French fry) samples were evaluated visually and scored according to 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.  Scores presented in the tables are an average of the five slabs in each sample.