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.
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.