Tina Brandt
Gale E. Kleinkopf

The first year of this study, on the 1998 crop, has been completed.  The second year of the study is now underway.  This report details the 1998 crop year potatoes only.  The study design for the 1999 crop is the same except the potatoes were grown in Kimberly, the Russet Legend cultivar has been replaced by A84118-3 and fry color analysis using a reflectometer will be done at each sugar sampling.

Five varieties of potatoes were grown at Aberdeen in 1998.  Two thousand pounds of each variety were brought to the Kimberly potato storage facility on Sept. 29, 1998.  Storage boxes were filled using field-run tubers on Sept. 30, 1998.  The storage experimental design involves five varieties; Russet Burbank, Ranger Russet, Gem Russet, Legend and Umatilla, three storage temperatures: 42, 45, and 48 F and sprout inhibited with CIPC versus non-inhibited.  There are three reps per variety/storage temp/sprout inhibitor treatment combination.  Dormancy break in all three reps of the 30 treatment combinations was monitored.  Sprout lengths and weights were recorded monthly.  Response of the varieties to CIPC treatment and storage temperature was followed throughout the storage season.  Sugar samples were taken monthly and both pre and post CIPC application.  The baseline sugar samples were taken on Oct. 15, 1998.  Fry color analysis was performed beginning in February and continued monthly, concurrent with sugar analysis, through June.  Fry color determination was achieved on 20 strips per sample (2 from each tuber), strips were fried in canola oil at 375 F for 3.5 minutes, subjective ratings were made using the USDA fry color chart and the scale of 0 to 4.  CIPC residue analysis was performed on one replication per month from December through June.  The University of Idaho Food Quality Assurance Laboratory in Twin Falls, ID processed these residue samples.

Differences in dormancy length were observed among the varieties tested (see Table 1).  In the non-CIPC treated samples we saw the Russet Legend, Ranger Russet, and Gem Russet had a dormancy length of 90-100 days when stored at 45 F, while the Russet Burbank and Umatilla Russet varieties had a dormancy of 110-120 days.  The data for the three storage temperatures can be seen in Figures 1-3.  The dormancy groupings observed at 45 F are consistent across the three storage temperatures, however, the actual dormancy length is influenced by temperature.  At 42 F, in general, dormancy break is delayed relative to the 45 F storage by nearly 60 days.  At 48 F, dormancy break is about 15 days earlier than occurs in the 45?F storage.

Glucose analysis in the five varieties from three storage temperatures revealed many significant differences.  Data is shown in Figures 4-6. We saw no significant differences in glucose concentrations as a result of the CIPC sprout inhibitor treatment in any of the cultivars.  There was a larger spread of glucose concentrations among varieties when stored at 42 F as compared to 45 or 48 F.  In general, sugar concentrations were highest at 42 F.  The glucose levels were nearly the same for each cultivar at 45 and 48?F.  Ranger Russet exhibited the highest glucose concentrations at all three temperatures beginning approximately 150 days after harvest. Umatilla Russet had the lowest glucose concentrations at all three storage temperatures, furthermore, it was significantly lower than all other varieties when stored at 42 F.  The mean fry color (Figure 7) was correspondingly lowest for Umatilla Russet at 42 F, indicating this variety stores well, even for processing, at the low temperature.  Sucrose data was collected for all varieties at all temperatures plus and minus CIPC as well.  Gem Russet generally had the highest sucrose concentrations.  At 45 and 48 F it was just slightly, but usually significantly higher than the other varieties.  At 42 F, however, it was significantly higher that he other varieties from 90 to 180 days after harvest.  At that point, the levels decreased and were similar to the other varieites.

Fry color ratings were determined each month beginning in February on the exact same potatoes as those used in glucose and sucrose determination. Figures 7-9 show the mean fry color ratings.  These fry colors were determined subjectively on a scale of 0 to 4, using the USDA fry color chart.  The fry color ratings corresponded quite well with the glucose concentrations with a few exceptions.   We observed some variability between sampling dates that is probably due to the subjective judgement and not true sugar differences (we did not see corresponding changes in the sugar concentrations).  The fry color data can be reliably compared within a sampling, between varieties and temperatures, but not between sampling dates. We have altered the protocol this year and are using a reflectometer to more objectively determine fry color.   Fry analysis included ratings for mottling and sugar end.  No mottling problems were observed in any of the varieties.  We observed a lower incidence of sugar end in Gem Russet than the other varieties.

CIPC residues were monitored throughout the storage season (see Figures 9-12).  This data represents only one replication per variety/storage temperature treatment so we were unable to perform statistics on this data.  We did not see any obvious differences in residues among varieties.  We did start to see some sprouting in the CIPC treated Ranger Russet and Legend Russet potatoes stored at all three temperatures after March (data available).  Sprout length was increased with increasing storage temperatures in both varieties.  This sprout growth indicates that perhaps Ranger Russet and Legend require higher CIPC residues to inhibit sprouting than the other varieties in this test.

PROJECTIONS:

In this test, some varieties compared very favorably to Russet Burbank in terms of storability.  Dormancy length in Umatilla Russet was equal to Russet Burbank.  Gem Russet, Ranger Russet and Russet Legend had similar dormancy periods.  However it appears that Russet Legend and Ranger Russet require higher CIPC residues to maintain sprout inhibition late in the season than the other varieties tested.   Russet Gem and Umatilla Russet generally had sugar concentrations equal to or lower than Russet Burbank.  Ranger Russet showed an increase in glucose concentrations and an increase in fry color after approximately 120-150 days in storage at 42, 45, and 48 F.  Umatilla Russet maintains very low sugar concentrations and fry colors at the 42 F storage.  This may be especially useful for seed growers, giving them the option to sell some of their potatoes on the open market later in the storage season.

PUBLICATIONS:

Kleinkopf, Gale E. (1999).  New Research in Potato Storage.  18th Annual National Potato Council Seed Seminar.  Dec 2-4.  Abstract.

Kleinkopf, Gale E. and Nora Olsen. (1999).  Storage Workshop.  31st Annual University of Idaho Potato Conference.  Jan 20-21.
Results: