Establishment of supply system for summer-to-autumn-flowering, small-flowered, spray-type chrysanthemums to meet the peak demand from July to September utilizing night interruption treatments

The supply system of summer-to-autumn-flowering, small-flowered, spray-type chrysanthemums was investigated to meet the peak demand from July to September (at the beginning of July and August, and middle of September), using plant cuttings obtained from the same mother stock, which were subjected to night interruption (NI) treatment. In addition, techniques for the fine regulation of flowering after budding were investigated. Further, regulation of spray formation using interrupted lighting (IL) after the NI treatment was investigated. 1. Techniques for the peak demand supply from July to September using the same cultivars Selection of cultivars that can be used to meet the peak demand from July to September, as well as the peak demand supply of the selected cultivars during this period were investigated. A total of 115 cultivars that flower from June to September under natural day length (NDL) were collected, of which 15 were selected based on early flower budding under NDL and marked suppression by NI. Four of these cultivars, namely 'Seikomaki', 'Haruka', 'Subaru', and 'Seichigusa', could meet the peak demand from July to September when subjected to NI treatment. 2. Techniques for fine regulation of flowering after budding Techniques for the fine regulation of flowering after budding were investigated to establish a stable supply during the peak demand period. First, flowering-acceleration techniques were investigated. Application of gibberellic acid (GA) (100-200 ppm, twice) after the flower bud break stage accelerated flowering by a few days without any major effect on the cut flower characteristics. Next, a flowering-suppression technique, which was achieved by incorporating shading after budding, was investigated; 80% shading markedly delayed flowering after budding until the end of the flowering period, although the number of capitura was decreased. Finally, flowering-suppression techniques by IL after budding were investigated. The combination of IL for 10 days from the day of budding, with 4-6 h of NI per day, delayed flowering by a few days without any major effect on the cut flower characteristics. 3. Techniques for the regulation of spray formation using IL Techniques for the regulation of spray formation using IL after the NI treatment were investigated. The effects of the NDL period before IL application and the IL period on spray formation of the cut flowers harvested in August are discussed. Spray formation could be regulated by the application of IL for 8-20 days after 2-6 days of NDL treatment in August. Similar experiments were conducted on flowers that were to be harvested in September; it was observed that spray formation could be regulated by IL treatment for 8 days after 2-6 days of NDL treatment. 4. High precision supply system to meet the peak demand from July to September The high-precision supply system was analyzed to meet the peak demand from July to September by combining the peak demand-supply technique using the same cultivars and the techniques for the fine regulation of flowering. Appropriate dates of the end of NI treatment and 50% budding were identified from previously collected data. The NI treatment was stopped on the day predicted for flowering or 5 days prior to that, and then the date of budding was confirmed. If the budding date was earlier than that predicted, IL was applied from the date of budding. In contrast, if the budding date was later than that predicted, GA was applied after budding. Thus, in any cropping system, it was possible to match the flowering date with the target date within 1 day. Thus, it can be concluded that the high-precision peak demand-supply system of the small-flowered, spray-type chrysanthemums from July to September, developed in this study, is highly feasible.