Heat tolerance and cold tolerance of cultivated potatoes measured by the chlorophyll-fluorescence method.

Heat and cold tolerances were determined for 13 clones of the commonly cultivated potato, Solanum tuberosum L. Five clones were considered to be adapted to warm climates and the others to cool climates only in terms of their ability to produce tubers. The decrease in the rate of the induced rise in chlorophyll fluorescence after heating leaves at 41°C for 10 min was used to measure relative heat tolerance, and the decrease following chilling at 0°C was used to measure relative cold tolerance. The warm-adapted clones all showed enhanced heat tolerance compared with the cool-adapted clones. Higher heat tolerance was also correlated with a greater tolerance towards a cold stress of 0°C and it is suggested that the warm-adapted clones were selections showing an increased generalized capacity to withstand environmental stresses of several kinds rather than a specific genotypic adaptation to tolerate warm temperatures. Heat and cold tolerances were also determined for several other species of potato cultivated in the Andean region of South America. Of these, S. phureja, which is found at low altitudes on the eastern slopes of the Andes, showed a tolerance to heat comparable to that of the warm-adapted clones of the common potato, the two most heat tolerant of which contained some phureja in their parentage. Diploid and triploid species of cultivated potatoes were considerably more cold tolerant than the clones of the common potato, a tetraploid. The genetic variability for heat and cold tolerance in cultivated and wild potatoes is discussed in relation to increasing the tolerance of the potato to these stresses.