Heat Tolerance in Diploid Wild Potato Species In Vitro

Potatoes are a cool season crop. Yet, with growth in the world population and rising temperatures, more heat tolerant cultivars are going to be needed. The objectives of this work were to identify heat tolerance in diploid wild Solanum species, as measured by the ability to form microtubers in tissue culture, and to compare four different methods of evaluating heat tolerance. In each of five experiments conducted over time, four nodal cuttings from up to 20 genotypes from each of ten diploid wild potato species were grown in MS medium supplemented with 8% sucrose and cultured at 19 degrees C (cool) and 25 degrees C (warm) in the dark. Four methods were used to evaluate heat tolerance: percent microtuberization under warm conditions, difference in percent microtuberization between cool and warm conditions, microtuber yield under warm conditions, and the difference in microtuber yield between cool and warm conditions. Species were ranked for each of these four methods (with rank=1 being most heat tolerant) and ranks were summed across the four methods to identify the most heat tolerant. There were significant differences among species and the species x temperature interaction was significant for percent microtuberization and microtuber yield. Percent microtuberization in five of the species was similar under cool and warm temperatures; greater under cool temperatures for three species; and, greater under warm temperatures for two species. Microtuber yield in four of the species was similar under cool and warm temperatures; greater under cool temperatures for six species; and, greater under warm temperatures for one species. Rankings of heat tolerance among the species varied by the method used, but S. kurtzianum and S. sogarandinum were the most heat tolerant.