The Effect of Field Heat Reduction Methods on Fresh and Processing Qualities of Red and Russet Potato Cultivars

The effect of three field heat reduction methods, including temperature lowering stepwise (TLS), temperature lowering gradually (TLG), and temperature lowering immediately (TLI), after harvesting on the quality of Russet Norkotah 3 and red skin numbered line CO 07102-1R potatoes were investigated. The tubers were analyzed at harvest (0 time), when they reached 3 °C, and after 6 months of storage at 3 °C for physiological weight loss, firmness, wound healing, total phenolics content, reducing sugars, and color of french fries. The results indicated that weight and firmness losses were lower under the TLS reduction method after 6 months of storage than TLG and TLI methods. The weight loss in TLS is 12%, TLG 14% and TLI 17% in CO 07102-1R whereas Russet Norkotah TLS is 4%, TLG 6%, and TLI 8% respectively. Wound healing was more effective using the TLS reduction method, especially in Russet Norkotah 3. French fry color was lighter at harvest (USDA grade 0), while there were no differences in the color of French fries prepared from tubers stored under the TLS and TLG methods (both had USDA grade 2). French fries were darker for tubers from the TLI method (USDA grade 4). The total phenolic content and reducing sugars were significantly increased in the TLI field heat reduction method. Keywords: Potato, Storage management, Wound healing, Weight loss, French fry

Genome-Wide Association and Genomic Prediction for Fry Color in Potato

Potatoes destined for crisping are normally stored above 8 degrees; below this glucose accumulates leading to very dark fry colors and potential acrylamide build up. Unfortunately, sprouting occurs above 4 degrees and impacts product quality, necessitating the use of sprout suppressant chemicals. Therefore, a goal of breeders is to develop potatoes with excellent fry color, which is maintained under storage below 8 degrees. Genomic or marker-assisted selection offers an opportunity to improve the efficiency of potato breeding and thereby assist breeders in achieving this goal. In this study, we have accumulated fry-color data on a large population of potato lines and combined this with genotypic data to carry out a GWAS and to evaluate accuracy of genomic prediction. We were able to identify a major QTL on chromosome 10 for fry color, and predict fry color with moderate accuracy using genome-wide markers. Furthermore, our results provide evidence that it is possible to identify a small subset of SNPs for processing characteristics that can give moderate predictive ability, albeit lower than that achieved with genome-wide markers.

The Interaction Effect of Carbon Dioxide and Ethylene in the Storage Atmosphere on Potato Fry Color Is Dose-related

Previous studies have shown that the fry color of stored potatoes (Solanum tuberosum L.) can be negatively affected by an interaction between elevated CO2 (2 kPa) and ethylene gas (0.5 μL·L−1) from various sources. Two consecutive trials were conducted during each of two storage seasons (2006 and 2007) to study the effects of varying concentrations of these two gases. In each year, CO2 at 0, 0.5, 1.0, or 2.0 kPa plus 0, 0.25, or 0.5 μL·L−1 ethylene was applied in a factorial design to ‘Russet Burbank’ tubers for 9 weeks. Trials that began in Jan. 2006 and Jan. 2007 comprised the dormant-tuber experiment; trials that began in Apr. 2006 and Apr. 2007 comprised the nondormant-tuber experiment. Fry color of the tubers was evaluated at the start of each trial and thereafter at intervals of 3 weeks. In all trials, when tubers were exposed to different concentrations of CO2 but without ethylene, fry color was the same as in untreated controls. When only ethylene was applied, the fry color was 7 to 22 Agtron percent reflectance units darker than the controls. In the nondormant-tuber experiment, the darkening resulting from ethylene was dose-related, in agreement with previous research. When the tubers were exposed to both CO2 and ethylene, dose-related responses to both gases were observed in the nondormant-tuber experiment, i.e., fry color was darker with an increase in either CO2 or ethylene when both gases were present. Neither the dose–response to ethylene nor the interaction between ethylene and CO2 was statistically significant in the dormant-tuber experiment. In both experiments, the darkest color was observed when both gases were present at the highest concentrations. A dose–response of potato fry color to CO2 in the presence of ethylene has not been reported previously.

1-Methylcyclopropene Counteracts Fry Color Darkening Attributable to Carbon Dioxide and Ethylene Interaction

The fry color of potatoes (Solanum tuberosum L.) stored for processing remains an important quality characteristic that can be affected by many factors, including ethylene gas from various sources and the interaction of very low concentrations of ethylene gas (less than 1 μL·L−1) and accumulated CO2. Because previous studies show that pretreatment with 1-methylcyclopropene (1-MCP) can substantially reduce fry color darkening attributable to applied ethylene, we hypothesized that 1-MCP could also reduce fry color darkening attributable to the interaction of ethylene and CO2. Trials were conducted over two storage seasons, using ‘Russet Burbank’ tubers, either untreated or treated with 0.5 μL·L−1 ethylene gas ± 2 kPa CO2 and ± 1-MCP. Tubers exposed to ethylene gas had darker fry color than untreated tubers, whereas the fry color of tubers exposed to ethylene plus CO2 was darker still. However, the fry color of tubers pretreated with 1-MCP was as light as that of the untreated tubers. This provides a potential new tool for the potato industry to manage potato fry color of stored processing potatoes.

Carbon Dioxide and Ethylene: A Combined Influence on Potato Fry Color

For many years, the accepted wisdom among potato storage researchers and industry personnel linked the accumulation of CO2 in the storage atmosphere to darkening of potato fry color. Dark fry color is undesirable in the potato processing industry, as consumers prefer light-colored finished products. Previous research to elucidate the effect of CO2 has presented conflicting results. In three consecutive years of storage trials, the effects of elevated CO2 concentrations, reduced O2 concentrations and ethylene gas on the fry color and sugar content of `Russet Burbank' potato (Solanum tuberosum L.) tubers were evaluated. The potatoes were stored in modified atmosphere chambers and selected atmosphere mixtures were supplied from compressed gas cylinders. Four 3-week trials were conducted in 2002 and two 9-week trials were conducted in each of 2003 and 2004. Fry color and tuber sugars were assessed at the start of each trial and after several weeks of exposure to the treatment atmospheres. Compared with untreated controls, increased CO2 alone or in combination with decreased O2 had little or no effect on fry color or tuber sugars. During the second and third years, only selected treatments were repeated, with or without the addition of 0.5 μL·L–1 ethylene gas. Ethylene is known to affect potato fry color and reducing sugars. In three of four trials, tubers exposed to ethylene alone had darker fry color and higher reducing sugars compared with controls. Applied treatments had little or no effect on fry color and sugars in the fourth trial. Interestingly, in the same three of four trials, fry color of tubers exposed to both elevated CO2 and ethylene gas was not only darker than controls but also darker than tubers treated with ethylene alone. Similarly, reducing sugar concentrations were higher in tubers exposed to both ethylene and CO2 than with ethylene alone. No similar interaction between ethylene and oxygen concentration was observed. The results suggest a synergistic negative effect of trace ethylene and elevated CO2 on fry color, which may explain the apparently contradictory findings of some published research examining the effects of CO2 on potato fry color.

Carbon Dioxide Is a Promoter of Ethylene Action in Potato Tubers

In three consecutive years of storage trials, the effects of reduced O2 levels, elevated CO2 levels, and ethylene on the fry color and sugar content [sucrose and reducing sugars (glucose and fructose)] of `Russet Burbank' potato (Solanumtuberosum L.) tubers were evaluated. The potatoes were stored in modified atmosphere chambers and the atmosphere mixtures were supplied from compressed gas cylinders. Fry color and sugar content were assessed at the start of each trial and after several weeks of exposure to the treatment atmospheres. Four 4-week trials were conducted in 2002 and two 9-week trials were conducted in each of 2003 and 2004. No differences in fry color or sugar content attributable to either increased CO2 or decreased O2 were observed, compared with untreated controls, in any year. In the second and third years, only selected treatments were repeated, with or without 0.5 μL·L-1 ethylene. Ethylene alone caused a moderate darkening of fry color and an increase in reducing sugars. However, the fry color and reducing sugar content of tubers exposed to a combination of elevated CO2 and ethylene were considerably darker and higher, respectively, than observed with ethylene alone. No similar interaction between ethylene and O2 level was observed. These results suggest that CO2 promoted ethylene-induced fry color darkening, which may explain the contradictory effects of CO2 on fry color frequently observed by the potato industry. This is contrary to published research on other fruits and vegetables, which has generally shown that CO2 inhibits ethylene action.

Using Ethylene as a Sprout Control Agent in Stored `Russet Burbank' Potatoes

The effect of ethylene on tuber sprout growth and quality in potato (Solanum tuberosum L. `Russet Burbank') was tested in laboratory and commercial studies for 6 and 3 years, respectively, in comparison with untreated (laboratory study) and CIPC-treated tubers (laboratory and commercial studies). In both studies, ethylene was applied continuously at 166 μmol·m-3 for at least 25 weeks, beginning in early December (laboratory study) or early December to early January (commercial study). In the laboratory study, ethylene delayed the appearance of sprouts for 5 to 15 weeks, compared with untreated tubers. In the ethylene-treated tubers in both studies, sprouts appeared on many eyes but most of them remained very small (<5 mm long). Longer sprouts (>5 mm) appeared after 15 weeks but did not exceed 12 and 59 mm in the laboratory and commercial studies, respectively. Sprouts on ethylene-treated tubers were more easily detached up to 6 weeks after ethylene treatment ended, compared with untreated tubers. In both studies, ethylene treatment was not associated with decay, disorder or internal sprouting problems. In both studies, the Agtron fry color [or U.S. Dept. of Agriculture (USDA) color grade] of ethylene-treated tubers was darker than CIPC-treated tubers at almost all sampling times. Continuous exposure to ethylene was an effective sprout control agent but it produced a darker fry color, compared with CIPC-treated potatoes.