Specific gravity of Russet Burbank potatoes

Variability in specific gravity of Russet Burbank potatoes was documented in a single 32 hectare field. Maximum variation was 40 units among individual tubers within hills (one unit equals one part in 1000th of specific gravity measurement) and 15 units among hills. Field site variability of 10–15 units was common between sampled grid lines in the field; but bulked samples (truckloads) reduced the sampled variability to 8–10 units. When the samples were taken from bulked lots as opposed to single hill samples, the variability decreased. Grower lots, which were pooled samples from several truckloads, showed specific gravity differences of 2–7 units even though all lots were from the same field. These variations among specific gravity samples should be taken into account when considering total solids content in any lot of potatoes. Degree of russetting of the skin and hollow heart also influenced specific gravity measurements. Measured differences between peeled and unpeeled lots of 10 units in specific gravity corresponded to 2% difference in total solids content. Statistically, the variance of the peeled lot was one half that of the unpeeled lot, therefore, to minimize the measured differences due to skin type, peeled potatoes could be used for the specific gravity measurements.     

Some factors influencing shear force determinations of Norgold Russet and Russet Burbank potatoes

Norgold Russet did not increase in shear force readings with growth and development as did the raw product of Russet Burbank which showed a progressive increase in readings with growth during the latter half of the season. Seasonal differences were apparent with Russet Burbank, but not for Norgold Russet during the 3 years of this study. Higher shear force readings were recorded with an increase of specific gravity of Russet Burbank, but not for Norgold Russet. Low fertility level resulted in slightly higher shear force values possibly because of enhanced maturity. No major influence of moisture stress was evident. Higher shear force values resulted from longer periods of storage and with higher storage temperatures of Russet Burbank within the range of 34F to 45F.     

Respiration rates and sugar accumulation in normal and moisture stressed Russet Burbank potatoes

Studies were made on Russet Burbank tubers grown under normal and moisture stressed conditions. Stressing the tubers caused increased reducing sugar accumulation in the basal end during storage. Respiration rates of apical and basal portions of stressed and normal tubers were followed during the growing season and in storage. Although its sugar content was greater, the basal end of stressed tubers respired at a significally slower rate than apical ends from the same tubers. Normal basal and apical portions showed no statistical differences in respiration although the apical end respired at a slightly faster rate than the basal end. A positive linear correlation between sugar concentration and respiration rate of the apical portion was obtained. Differences were found in the abilities of apical and basal ends to alter respiration rates in response to changes in sugar concentration. The resprationof the apical end was the more sensitive to increased sugar concentration. The basal end of stressed tubers lost some of its ability to respond, probably because of increased physiological aging caused by the stress conditions.     

Relationships between fry color and sugar concentration in stored Russet Burbank and Shepody potatoes

Relationships between french fry color and sugar composition of Russet Burbank and Shepody potatoes harvested at various chemical maturities (i.e., sucrose concentrations) and exposed to various temperature regimes during 8 to 9 months storage were examined. Combined data from 3 years of study showed fry color to be more closely associated with glucose during 8 C storage for Russet Burbank (r²=0.65) and Shepody (r²=0.62) than with fructose, total reducing sugars, sucrose, or total sugars. Glucose > 1.6 mg g^?1 in Russet Burbank and > 1.2 mg g^?1 in Shepody resulted in fries which were too dark to be eligible for maximum bonus paid by processors for good color. Russet Burbank harvested with sucrose > 3.1 mg g^?1 and Shepody harvested with sucrose > 1.6 mg g^?1 and preconditioned for 14 d at 15 C before storage at 8 C accumulated enough glucose in storage to result in fries which were darker than was acceptable for maximum bonus payment. Preconditioning at 15 C for 70 d was necessary to prevent Russet Burbank with sucrose of 3.9 mg g^?1 at harvest from accumulating unacceptably high glucose during storage. Glucose determined with enzymatic test strips was in close agreement with that by HPLC for both cultivars. The test strips could be used to estimate fry color of Russet Burbank.     

Some factors influencing the pH of apical and basal portions of Russet Burbank and Norgold Russet potatoes

Studies were made of pH changes of apical and basal portions of Russet Burbank and Norgold Russet potatoes during growth and in storage. Russet Burbank had a higher pH of the apical portion during the later stages of growth as compared to the basal portion. No significant differences between the two portions were found during growth with Norgold Russet. After a period of moisture stress the pH of the basal portion of Russet Burbank dropped significantly. The basal portion of both varieties at higher specific gravities had higher pH after storage than the apical portion. A highly significant negative correlation was obtained after storage between reducing sugar levels of tubers of different specific gravities and pH levels in both varieties. There were no significant differences in pH among storage temperatures of 34, 38, 42 and 45 F. However, the pH level at 48 F storage was significantly higher than at the other temperatures. The pH level of tubers from seedlings and varieties were poorly correlated with their reducing sugar contents after storage. It appears that pH can be an indicator of potential chip color only within the confined limits of a specific lot.     

Sugar-end in Russet Burbank potatoes

Tissue selected from the stem- and bud-end of reconditioned tubers having sugar-end disorder was compared by color after frying and chemical composition to tissue removed from the two ends of tubers without sugar-end disorder taken directly from cold storage at 45 F, and after reconditioning 3 weeks at 70 F. Chemical analyses of selected tissue suggested that the dark finish-fry color at the stem-end of sugar-end tubers following reconditioning at 70 F was due to the inability of the physiological systems within the tissue to convert reducing sugars to starch and/or to use these sugars in the respiratory process. Of the components analyzed, only a high reducing sugar content was associated with a dark finish-fry color. Neither sucrose nor free amino acid content was associated with the sugar-end disorder. Extending the reconditioning period at 70 F for sugar-end tubers did not lower the reducing sugar content or the darkening of the stem-end tissue on frying.     

The influence of early storage (Pre-Holding) temperatures on sugar accumulation in Russet Burbank potatoes

The stem and bud portions of Russet Burbank tubers held at 70 F (21.1 C) for 2 weeks had significantly more reducing sugars at holding temperatures of 45 (7.2 C) and 42 F (5.6 C) than tubers immediately placed in 45 and 42 F storage. At a holding temperature of 48 F (8.9 C), no differences were found Two-week pre-holding temperatures of 42, 45, 56, and 70 F followed by a holding temperature of 42 F were compared. Sugar accumulations tended to be minimal at pre-holding temperatures of 48 to 50 F. Reducing sugar accumulation increased as pre-holding temperatures increased or decreased from this optimum. Longer periods of pre-holding temperatures at 48 F delayed sugar accumulation; however, the eventual total amounts of reducing sugars in May at a holding temperature of 42 F were similar, whether pre-holding periods were 1 to 2 months or 4 to 5 months     

Seed performance of Russet Burbank potatoes

A three-year study of three planting dates and four harvest dates of Russet Burbank seed potatoes was made to determine their effect on plant vigor, virus leaf roll infection, yield, size distribution and quality. Yields decreased significantly with delayed harvest of the seed crop. The incidence of late season virus leaf roll based on visual symptoms increased significantly with delayed harvests. The risk of a late season virus leaf roll infection increased when a later harvest was combined with a late planting. Seed taken from the earlier harvested plots consistently had earlier and more uniform emergence, the greatest vigor and the highest yields. The effect of planting date and harvest date had little effect on size distribution and no effect on specific gravity.     

Response of Russet Burbank potatoes to ethephon sprays

Ethephon ((2-chloroethyl)phosphonic acid) was sprayed on the foliage of Russet Burbank potatoes at tuber initiation in four separate field trials over two years. Rates were 0, 61, 122 and 183 g ai/ha. Total yield, yield of U.S. No. 1’s, hollow heart and brown center generally decreased at higher ethephon rates. Yield of undersized tubers increased. Ethephon sprays generally decreased specific gravity but the effect was minor and not consistent. In three of the four plantings where hollow heart and brown center in the untreated controls exceeded 8 t/ha, the low rate of ethephon increased the yield of non-hollow tubers ≥56 g in size.     

Field performance of transgenic Russet Burbank and Lemhi Russet potatoes

Transformed Russet Burbank and Lemhi Russet clones which contained three different transgene constructs were evaluated for performance under field conditions in Idaho. The transgenic lines were characterized over two growing seasons, using plants grown from both greenhouse produced minitubers (first year) and field grown seed (second year). Individual clones were evaluated for a variety of agronomic and quality properties. Many of the transformed clones showed reduced yield and increases in percent malformed and undersized tubers. Other characteristics, such as specific gravity and fry color, showed less variability. The variation observed in non-transgenic clones regenerated from tissue culture was less than that of the transformed lines. Out of an original population of 57 transgenic lines in tissue culture, maintenance of key agronomic and quality properties of the parental material was observed in only four clones. These results suggest that experiments designed to generate transgenic lines for the marketplace should be initiated with a large number of transgenic clones.     

Relative differences in sugar content of basal and apical portions of Russet Burbank potatoes

Basal and apical portions of mature and immature Russet Burbank tubers stored at 42 F (5.6 C), 45 F (7.2 C), and 48 F (8.0 C) were analyzed for sucrose and reducing sugars at seven monthly intervals for three seasons. Percent relative difference of reducing sugars (between mature and immature tubers) was greater in the apical than the basal portion. On the other hand, seasonal differences in percent reducing sugars were reflected more in the basal portion by greater relative differences among seasons than in the apical portion. Statistical analysis showed no trend or influence of maturity or storage temperature in affecting the relativeratio of reducing sugars between the basal and apical portions. Differences among growing seasons appeared to affect this ratio. Tubers from the 1970–71 season had more equal relative amounts of sugars in the two portions than did the tubers from 1968–69 or 1969–70 seasons. Ratio ofsucrose between the basal and apical portions was not affected appreciably by maturity, storage temperature or season, although immaturity and lower storage temperatures caused slightly greater overall sucrose accumulation. Sucrose and reducing sugar contents were poorly correlated regardless of maturity, storage temperature or different seasons.     

CIPC residues on stored Russet Burbank potatoes: 1. Maximum label application

Residue concentrations of chlorpropham (CIPC) on stored Russet Burbank potatoes were evaluated after thermal aerosol treatment at maximum labeled rates. The aerosol was applied after the potatoes had been placed in the storage structure and the wound healing process was complete. Average residue concentrations four days after the initial application ranged from 6 to 8 mg/kg fresh tuber weight depending on the storage temperature and the application rates. A second aerosol treatment applied 90 days after the first treatment kept the residue concentrations above 5 mg/kg for the duration of the storage period. A direct spray application to the tubers at various times during the study raised the average CIPC concentration an additional 2 to 3 mg/kg. All CIPC residue concentrations measured on tubers in this study were below the EPA established (1996) tolerance of 30 mg/kg. Residue concentrations of CIPC were greater on potatoes near the bottom of the pile than near the top of the pile. These variations in CIPC residue concentrations (3–8 mg/kg between top and bottom of the bulk pile) are appropriate justification for the development of improved application methodology.     

Factors influencing reconditioning of Russet Burbank potatoes

Studies were made to determine factors which influence reconditioning of Russet Burbank tubers. Tubers from plants grown under low fertility were more difficult to recondition than tubers from plants adequately fertilized. Low specific gravity potatoes were also more difficult to recondition than high specific gravity potatoes even though the initial sugar content was approximately equal. The stem portion of Russet Burbank tubers lost considerably less sugars than the bud portion during the reconditioning process. It appears that factors which are responsible for high sugar development are also responsible for difficulty in sugar loss. Results also indicate greater difficulty in reconditioning early in the storage period with the loss of sugars becoming easier as the storage season progressed into spring.     

Comparison of sensory differences of stored Russet Burbank potatoes treated with CIPC and alternative sprout inhibitors

The sensory properties of Russet Burbank potatoes treated with three naturally occurring volatile compounds, as alternatives to CIPC for sprout inhibition, were evaluated. Potatoes from the 1995 and 1996 crop years were treated with salicylaldehyde, 1,8-cineole, 1,4-dimethylnaphthalene, or CIPC prior to dormancy break during storage and stored for up to 16 wk. Sensory differences between potatoes treated with alternative sprout inhibitors and CIPC-treated or untreated potatoes and inhibitor concentration were determined at 2-wk intervals. Potatoes treated with 1,8-cineole or salicylaldehyde, but not 1,4-dimethylnaphthalene, were significantly different from the untreated potatoes or potatoes treated with CIPC. Sensory detection threshold levels for the alternative inhibitors were measured in a model potato system. The residual levels of the sprout inhibitors were within the detection threshold range for 1,8-cineole (0.02–0.04 ppm), but not for salicylaldehyde (0.0–0.10 ppm) or 1,4-dimethylnaphthalene (0.80–1.40 ppm). The presence of the residual sprout inhibitors and/or the influence of sprout inhibitors on potato metabolism during storage contributed to observed differences in sensory quality of stored potatoes.     

Response of Russet Burbank potatoes to soil fumigation and nitrogen fertilizers

Two field studies were conducted to determine the effects of soil fumigation on the response of Russet Burbank potatoes (Solanum tuberosum L.) to NH₄-N or NH₄NO₃ fertilizers. In one study fumigation increased yields but N source had no effect. In the other study fumigation had no effect but NH₄-N provided higher yields than NH₄NO₃. Microbial studies indicated that although populations of nitrifying bacteria were initially altered by fumigation, nitrification rates were similar to those in non-fumigated soil. In a controlled environment study in which potatoes were grown in fumigated field soil, neither N source nor fumigation had any effect on growth or yield. These studies indicated that fumigation had no effect on the response of potatoes to NH₄-N or NH₄NO₃ fertilizers.     

Internal quality of Russet Burbank potatoes following chilling

Russet Burbank potatoes were chilled at 25 F (?3.8 C), 27.5 F (?2.5 C), or 30 F (?1.1 C) for various periods of time and were then held at 45 F (7.2 C) for one or four weeks before testing. Susceptibility to injury was quite variable between the two crops and among tubers of the same lot exposed to the same treatment. The greatest amount of low temperature breakdown occurred in tubers chilled at 27.5 F (?2.5 C) for 10 hours. Flesh color, reducing sugar content, mealiness, and amount of sloughing in tubers that survived chilling were not markedly different from those in control samples although certain trends were observed indicating that the quality of chilled tubers was beginning to deteriorate. Chilling increased yellowness of flesh color in most treatments and darkness in several. Chilled tubers had a reducing sugar content slightly to moderately higher than the controls. They sloughed less than the controls and tended to be less mealy