Injury to potato leaves exposed to subzero temperatures in the absence of freezing

Electrolyte leakage was measured in "hardened" and "nonhardened" leaves of three potato species, Solanum tuberosum L., S. acaule Bitt. and S. commersonii Dun., and one interspecific cross, "Alaska Frostless" (S. acaule x S. tuberosum) when exposed to various subzero temperatures. The leaves were undercooled (no ice present) from 0°C to -12.5°C for 45 min and to-4°C for up to 10 d. Regardless of the degree of undercooling no injury was observed in any of the potatoes, "hardened" or "nonhardened", for up to 12 h. After 5 d, however, electrolyte leakage was observed in "hardened" S. tuberosum, S. acaule and S. commersonii, and in "nonhardened" "Alaska Frostless". After 10 d exposure all potatoes, "hardened" and "nonhardened", showed a significant amount of electrolyte leakage as compared to their controls kept at 0°C for 10 d.