QY of non-stressed plants was lower than that of dark-adapted plants and also showed a positive but non-significant correlation with WLT in some cases. The reason for this could be that the plants were stressed by other factors in the hydroponic system, even if the solution was aerated. However, the results for the Norwegian cultivars with and without aeration confirm that the increased fluorescence of plants growth in oxygen-depleted solution is related to oxygen stress and not only to an improved genotype in general