On the role of the light regime in root development of Euphorbia pulcherrima leafy stem cuttings

The development of primordial roots of Euphorbia pulcherrima cuttings coincides with a significant increase in photosynthesis. Therefore, Svenson and Davies (1990) suggested that supplementary lighting has no effect on root development of Euphorbia pulcherrima cuttings before primordial roots develop. In this study this hypothesis was experimentally challenged. Cuttings were cultivated with supplementary lighting from the day of sticking and compared to cuttings that were exposed to the same lighting after primordial root development. Our data show that both sets of cuttings developed equally well and both did better than cuttings that were cultivated without supplementary light. Moreover, the data show that light quality had a major impact on root number, length and weight. Therefore, this study confirms the hypothesis of Svenson and Davies (1990) and shows that the positive effect of supplementary lighting is partially mediated by photoreceptors.

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