Effect of stock plant lighting on bulk vegetative propagation of hybrid larch ( Larix× eurolepis Henry)

Bulk vegetative propagation through rooted cuttings is a way to enhance the number of plants produced by seeds of valuable batches of hybrid larch. Four experiments were conducted between 1992 and 1995 to investigate stock plant lighting management and its effects on the number of expected cuttings per plant and on rooting ability. A photosynthetic lighting complement (50 μmol s −1 m −2) was provided to stock plants between 5 a.m. to 11 p.m. when natural light intensity fell below 40 W m −2. It promoted the growth of stock plants and the number of cuttings collected, but it adversely affected the rooting percentage in the subsequent rooting of cuttings. The negative effect was stronger when light was applied at the end of the growing season. Experiments showed that photoperiodic lighting clearly decreased the rooting ability, both for stock plants raised in containers, in greenhouses or under white shaded tunnels and for stock plants grown in a nursery soil under a white shading tunnel. A photosynthetic complement, such as photoperiodic stock plant lighting, is not therefore justified for larch bulk propagation in our geographic area.