Propagation and Subsequent Growth of Rhododendron Cuttings: Varied Response to CO2 Enrichment and Supplementary Lighting

Abstract

Abstract CO2 mist (1100 μl CO2/liter) during fall propagation inhibited rooting of Rhododendron ‘Anna Rose Whitney’ (R. griersonianum × ‘Countess of Derby’) and had no effect on R. ‘Vulcan’ (‘Mars’ × R. griersonianum), R. ‘Unique’ (R. campylocarpum hybrid), R. ‘Anah Krushke’ (R. ponticum seedling), or R. ‘Pink Bountiful’ (R. williamsianum × ‘Linswegeanum’). Supplementary lighting from high-pressure sodium lamps (HPS) for 16 hr/day (0400 to 2000 hr) had no effect on rooting of any cultivar. There was an interaction between CO2 mist and HPS exposure on rooting in R. ‘Floriade’ (‘Britannia’ hybrid). CO2 mist inhibited and HPS stimulated shoot development during propagation. CO2 mist during propagation inhibited subsequent development of ‘Anna Rose Whitney’ and ‘Vulcan’. HPS during propagation inhibited subsequent growth of ‘Floriade’ and ‘Vulcan’. CO2 enrichment of stock plants prior to propagation did not affect rooting of R. ‘Sonata’, whereas CO2 mist during propagation was inhibitory. In ‘Anna Rose Whitney’, there was an interaction between CO2 enrichment before and during propagation. Application of supplementary HPS for 16 hr/day following propagation stimulated subsequent growth of both cultivars. CO2 mist during spring propagation stimulated rooting of ‘Pink Bountiful’ and ‘Vulcan’ and had no effect on R. ‘Matador’ (R. griersonianum × strigillosum), R. ‘Martha Isaacson’ (R. occidentale × Ostbo seedling No. 70), or R. ‘Elizabeth’ (R. forestii var repens × griersonianum). Supplementary HPS had no effect on rooting. A low irradiance night break treatment from incandescent lamps (2000 to 0400 hr) had no effect on rooting of ‘Vulcan’. There was an interaction between night break lighting and CO2 mist on rooting in ‘Unique’. CO2 mist and HPS during spring propagation had minor effects on subsequent growth of ‘Matador’, ‘Martha Isaacson’, ‘Pink Bountiful’, and ‘Elizabeth’. CO2 mist and supplementary HPS have little value in production of Rhododendron.