The present study aimed to investigate the effect of selenium on flowering indices, sex determination of flowers, and yield of cucumber plant under heavy metal stress conditions. Treatments consisted of selenium -0, 4, 6, 8 mgL−1- and heavy metals of cadmium -0, 20, 25 µM- and lead -0, 60, 100 µM-, which were applied in three stages during the experiment period. The results of this study showed that the stress of heavy metals with a negative effect on flowering indices resulted in delayed flowering and changing flower’s sex toward male flowers. Furthermore, delayed fruiting and significant decreases in fruit growth indices and total yield was observed in plants treated with cadmium and lead. Adding selenium to the culture medium resulted in accelerated flowering -reducing the time and number of nodes needed until the first flower emerges-, the emergence of more male flowers, increased the ratio of the number of female flowers to male flowers in plants under stress, and the highest effect of this element was observed at the concentration 6 mg/L. Based on this results, the application of 4and 6mg/L selenium in stress and non-stress conditions enhanced fruiting -a significant reduction in the time required from cultivation to fertilize the first flower and the formation of fruit in lower nodes- and significantly increased the number of fruits, fruit length and diameter, single fruit weight and total yield, and the greatest effect of this element was observed in 6 mg/L concentration. The results of this study showed that selenium has a positive effect on control of stress conditions and improvement of flowering indices and total yield in cucumber plant under the stress of heavy elements of lead and cadmium.

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