The measurement of the chlorophyll fluorescence efficiency of PSII is an effective and non-invasive technique to detect damage in PSII due to heat stress. As, potato is a cool season crop which makes it susceptible to higher temperatures. The effects of long exposure to range of temperature in the dark on wild genotype grown at 14-24oC or 24-34oC were investigated by means of chlorophyll fluorescence and other physiological traits. Exposure of plants grown at higher temperature in the dark led to a different level of inhibition of the rate of photosynthesis. Based on fv/fm indicator, we estimate the genotypic values and selected the first and last ranking genotypes from S. commersonii, S. chacoense and S. tuberosum and BEL, S. tuberosum cultivars was used kept as control. Selection was taken out by using Best Linear Unbiased Prediction (BLUP) model as proposed by Resende. Residual maximum likelihood (REML) measured component of variance suggested that the estimated physiological and chlorophyll fluorescence traits were worth to investigate and gives 68% accuracy in selection of genotypes. Analysis of variance highly shows significance among genotypes except stomatal conductance (Gs). While Pearsonâ€™s correlation of fv/fm was also checked for both temperature ranges. Under assumed normal temperature ranges none of the measured traits show significant correlation with fv/fm while under high temperature condition fv/fm was positively correlated with Y(ll), qP and ETR and moderate negatively correlate woth NPQ and qN. Physiological traits photosynthetic rate (Pn), stomatal conductance and transpiration rate (Tr) were higher for chacoense and followed by commersonii and tuberosum 2x. But overall, Gs of investigated wild genotypes were lower for higher temperature conditions but inverse for photosynthetic rates. S. chacoense genotypes showed 75% lower transpiration rates as compared to rest of the genotypes.