Temperature-induced fluorescence changes : a screening method for frost tolerance of potato (solanum sp.).

Field-grown tuber-bearing potatoes were screened for frost tolerance in a late stage of development. Three different clones of Solanum tuberosum L. and two interspecific crosses between clones of S. tuberosum and the wild potato species S. demissum Lindl. were studied. Two different methods were used. (a) Temperature-induced fluorescence changes of intact leaves were measured in freeze-thaw cycles between 20 degrees C and -10 degrees C. The variable fluorescence pattern was characterized in relation to frost tolerance. (b) Controlled freezings of plants in a climate chamber with successively increased low temperature stress, of 1 to 2 hours duration during the dark period. Freezing damages were classified visually.The short-term frost during the fluorescence measurement was compared with the long-term frost treatments in the climate chamber. The results of the two were identical to ranking of the different clones for frost tolerance. The temperature-induced fluorescence changes also monitored progressive damages to the chloroplast membranes when plants were exposed to successively lower temperatures in a controlled climate chamber freezing test. It was deduced from the fluorescence measurements that the freezing injury of potato occurs on the water splitting side of photosystem II.