ROOTING OF MICROCUTTINGS: UNMANIPULATED FACTORS
The leaf has in general a stimulating effect on adventitious rooting. Its presence is sometimes found to be compulsory at the cutting. The equiv Most perrential plants, herbaceous or lignous have a genetical structure that does not allow them to be consistently multiplied by means other than vegetative multiplication. Therefore the horticultural industry is largely dependant on adventitious rooting whether it be with classical multiplication methods or with in vitro micropropagation. Hence it is surprising to see that interest for work on adventitious rhizogenesis has declined over the last ten years, whereas it should be of great economical importance due to the development of in vitro microcutting techniques.
In addition, scientifically speaking, adventitious rooting represents a model whose study is likely to bring essential information for the understanding of the mechanisms involved in organogenesis in plants. Indeed a cutting is nothing but a plant brutaly separated from its source of minerals and water supplied by the roots. The reconstitution of the rooting system required deep modifications in the metabolism of the cutting : assuming a similar rooting ontogenesis for the majority of cuttings without pre-formed roots, these cuttings will not all be able to form a new rooting system.alence of the effects of leaves and buds can be illustrated by the behaviour of in vitro cuttings of Vitis with only one bud or leaf and with its axillary bud removed. The elements responsible for the activation of rooting seem to originate in the leaf during photosynthesis and then stored in the buds.
The comparative study of the rooting ontogenesis of mono-nodal Vitis cuttings, leaved or not, shows that the presence of the leaf has no influence on the speed of appearance of the earliest stages, but that the leaved cuttings reach quicker the stage "formation of rooting morphogenetic areas". The time advantage of these leaved cuttings increases as they come closer to the "emergence of the roots" stage (MONCOUSIN, 1987).