Abstract
1. To clarify the role of photosynthesis in the rooting of hardwood cuttings of grapevines (cv. Delaware), the effects of the darkness and disbudding treatments started at various stages of the propagation period on rooting were observed.
2. Distinct differences in the rooting of cuttings grown in darkness throughout the propagation period were found between the disbudded and undisbudded cuttings. This indicates that functions of the buds other than photosynthesis may play a significant role in rooting.
3. Darkness treatments started later than the 45th day after planting had little effect on either the rooting percentage or the root number of the undisbudded cuttings. This suggests that root initiation may be mostly completed by the 45th day after planting, when the first root appears.
Since the rates of apparent photosynthesis when rooting is initiated are quite low, as shown in a previous report (ref.), it may be assumed that root initiation is hardly affected by photosynthesis.
4. When darkness treatments were started later, better rootings were generally obtained through the latter half of the propagation period. Comparing the best rooted cuttings with the untreated controls, considerable differences were found in both root length and root weight. In view of these facts, it is possible that the root development is promoted by light during the latter half of the propagation period, and that photosynthesis may play a more important role in the development of roots after initiation.
