This study was carried out to identify potato cultivars with high combining abilities for heat tolerance and to get information about the individual performance of clones originated from crosses between heattolerant and heat-sensitive parents. Twenty six clonal families and more than 600 clones were assessed in warm and cool seasons in Brazil. High temperatures decreased tuber number and weight , resulting in 46% reduction in tuber yield. Furthermore, there was an eight-fold increase in tuber

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... ysiological disorders and a remarkable reduction in tuber specific gravity. General combining ability (GCA) x seasons and specific combining ability (SCA) x seasons interactions were significant for most traits, indicating that the best parents and families for the warm season were not the same for the cool season. However, as these interactions represented the average behavior of a large number of parents and families , it was possible to identify some outstanding parents and families for both seasons. Genetic variances among and within families showed that it is possible to obtain superior clones.