Monoploid genotypes (2n = x = 12), derived by anther culture of a diplandrous (2n pollen-producing) clone of Solanum phureja Juz. & Buk., a South American diploid potato species, were examined for their use in germplasm development. Nine monoploid genotypes and the anther-donor genotype were grown in three chambers (10-, 14-, and 18-hr daylengths) to examine the effect of photoperiod on tuber yield and to determine the variability for critical photoperiod for tuberization. Significant differences were found among the monoploid genotypes for tuber weight and tuber number. Longer photoperiod treatments decreased and delayed tuberization. Axillary tuber formation from single-node cuttings was used to estimate the onset of tuber induction and demonstrated variability among monoploid genotypes for critical photoperiod for tuberization.