한국화훼연구회지(2004) Abstract. The effects of different levels of irradiance on growth and flowering of chrysanthemum (Dendranthema grandiflorum) were examined at 12 h short and 16 h long photoperiods. Floral development, time to anthesis, and flower diameter were accelerated with increasing irradiance levels from 0.58 to 1.17 MJ·m-2·d-1 under 12 h photoperiod. Growth parameters such as total dry weight, leaf area, absolute growth rate (AGR), and net assimilation rate (NAR) were enhanced with increasing irradiance irrespective of 12 h or 16 h photoperiods. The development stage of flower bud (crown bud) formed after 7 weeks of 16 h photoperiodic treatment advanced and final leaf number decreased with increasing irradiance levels from 1.04 to 2.08 MJ·m-2·d-1, showing that flowering responses were promoted by increasing irradiance even under long photoperiod. Partitioning of carbohydrate to floral parts measured by flower weight ratio (FWR) also increased with increasing irradiance, suggesting that the flowers become a sink for carbohydrate to support their development. Additional key words: absolute growth rate, anthesis, Dendranthema grandiflorum, floral development, flower weight ratio, net assimilation rate