[Yield factors in starch production in potato (Solanum tuberosum L.) [cv Pimpernel]]

The object of the study was to determine the respiration rate and changes in the chemical composition (especially starch contents) in potato tubers (Solanum tuberosum L.) cv Pimpernel, due to maturity, storage time and reduction of the storage temperature. It was also related to the starch contents with the size of the tubers in the varieties Desiree, Kennebeck, Pimpernel and Yagana. In the first experiment, the respiration rate, dry matter and starch contents (on fresh and dry basis) were determined in Pimpernel (delivered by 2 farmers) harvested in three different times with an interval of 15 days. The potatoes were stored during 3 months at 10 deg C and 95% RH. The mean respiration rate of the trial was 4,67 mg CO2/kg h. This rate was not greatly influenced by the maturity (harvest time) of the tubers, the time of storage and the origin of the potatoes (farmers). In a short period of time, from the first to the last harvest, a sharp increase in starch content both in a fresh and in a dry basis, could be detected (2,5 g starch/100 g fresh potato and 6,6 g starch/100 g dry matter). A second experiment was conducted to determine the effect of a decrease of the storage temperature to 5 deg C (85% RH; held for 2 months), on the respiration rate and on the contents of total sugar, glucose, dry matter and starch of cv Pimpernel. The respiration rate was 3,46 mg CO2/kg h and 4,27 mg/CO2/kg h at 5 and 10 deg C respectively. The temperature decrease caused an increase in the contents of total sugar (0,25 g total sugar/100 g fresh potato) and glucose (0,19 g glucose/100 g fresh potato); the starch content increased in the tubers stored at 10 deg C. No substantial difference was detected due to the size of the tuber. It can be concluded that starch losses caused by respiration during storage and by decrease in storage temperature are low, but the time of harvest (maturity) can have important technical and economical consequences. Since, the starch contents on a dry basis varies with maturity, it is necessary to study if the starch contents determination based on specific gravity could give misleading results