Effects of high CO2 and low O2 atmospheres on the berry drop of ‘Kyoho’ grapes

To investigate the effects of low O2 and high CO2 atmospheres on the berry drop of ‘Kyoho’ grapes (Vitis vinifera X V. labrusca), changes of fruit detachment force (FDF) and berry abscission and enzyme activities in the abscission zone were examined during 60 days of storage in air (control), 4%O2 + 9%CO2 or 4%O2 + 30%CO2 at 0 °C and 95%relative humidity. There was a high negative correlation between FDF and berry drop. Cellulase activity increased over time and was closely correlated with berry abscission. Polygalacturonase (PG) activity rose markedly for the first 30 days and then remained relatively constant. Peroxidase (POD) activity dropped significantly for the first 15 days and subsequently rose sharply (P < 0.05). Cellulase, PG and POD activities were the lowest in fruits in 4%O2 + 30%CO2, followed by 4%O2 + 9%CO2 and air storage. Pectinesterase (PE) maintained a basal level of activity and there were no significant differences among three treatments (P < 0.05). Compared to air control, the combined effects of the lower level of O2 and the higher level of CO2 suppressed the activities of cellulase, PG and POD, maintained greater FDF, and reduced berry abscission during storage.