Growth and Flowering of Cymbidium Red Fire and Yokihi in Response to Light Intensity, Temperature and Nitrogen Nutrition during Night Interruption Forcing Culture

Abstract

The effects of night interruption (NI) with different light intensities, temperature and nitrogen nutrient control were examined on vegetative and reproductive growth of Cymbidium Red Fire and Yokihi. The cymbidium cultivars were grown under 9/15 h ambient light/dark (control), 9 h ambient light plus NI (22:00 to 02:00 h) with low light intensity at 3-7 mol m2 s1 (LNI) or 9 h ambient light plus NI with high light intensity at 120 mol m2 s1 (HNI) conditions. While none of the control plants flowered within 2 years, 100% of the Yokihi and 80% of the Red Fire plants grown under the HNI condition flowered. In the LNI group, 60% of the plants in both cultivars flowered. Plants in the HNI group showed a decreased time to visible inflorescence and flowering than those in the LNI group. Changes of carbohydrates including sucrose, fructose, glucose and starch were evaluated to determine the factors involved in flowering promotion in Cymbidium Red Fire during a NI forcing culture. Plants grown in the LNI and HNI had more leaves and pseudobulbs dry mass than those grown in the control group. Soluble carbohydrate concentrations in the pseudobulbs of the plants were greater in the HNI than in the LNI and control. Glucose was the most abundant soluble carbohydrate. Starch was present in the leaf exudate and was greater in the plants in the LNI than in the HNI or control. The growth and flowering of Cymbidium Red Fire and Yokihi plants were tried to improve flowering percentage during NI forcing culture with summer cooling. The greenhouses where the plants were grown were cooled by a mist system (mist) or a shade screen (shade). The temperature was approximately 2°C lower in the mist than in the shade and the relative humidity under the mist and shade condition were 80 ± 5% and 55 ± 5%, respectively. The plants that received NI followed by the mist flowered within 2 years with different flowering percentages depending on light intensity, while none of the plants flowered with the shade condition. Photosynthetic characteristics of Cymbidium Red Fire and Yokihi were investigated when the plants were exposed to NI forcing culture in relation to leaf nitrogen content. Photoinhibition could occur when NI applied to Cymbidium without supplemental nitrogen. The results of this study provide information on promotion of Cymbidium cultivation for high value cultivars. Application of the NI improved the flower quality of Cymbidium by decreasing days to flower. The NI promoted Cymbidium flowering within 2 years. Temperature should be maintained under 27°C by a mist system in a greenhouse cultivation to avoid heat stress and inflorescence abortion during summer growing seasons. Additional nitrogen should be fertilized when the NI is introduced in the forcing culture. The developed cultivation methods are beneficial to promote flowering and to enhance flower quality of Cymbidium Red Fire and Yokihi.