Solid ray floret of dahlia (Dahlia variabilis) cultivar ‘Nessho’ frequently exhibit color fading from autumn to spring. We have been maintaining the plants that produced an original red-colored capitulum in February 2012 as relatively low sensitive (RL) to low temperature plants and two plants that showed color-fading in June 2012 as relatively high sensitive (RH) to low temperature plants. Using cuttings obtained from three RL (RL1-, RL2-, and RL3-line) and two RH (RH1- and RH2-line) plants, color-fading occurrence in capitula was evaluated. From mid-October 2012 to mid-January 2013, the RL2-line plants exhibited a significantly lower extent of color fading index and a significantly higher number of completely red capitula than all RH-line plants when the minimum temperature was below 10°C. It was suggested that the RH-line plants had greater low temperature sensitivity and that they would decrease productivity of red-colored ‘Nessho’ capitulum. Any parasites would not contribute for the color fading occurrence in ‘Nessho’. From June to July 2017, a RL2-line plant produced color-faded capitula, and these plants would have RH characteristic. In conclusion, elimination of RH plants would be needed for suppressing the color fading occurrence of ‘Nessho’.

We investigated a plasma-based sterilization method for preventing Fusarium wilt disease in a spinach hydroponic system. Spinach seedlings were immersed in a Fusarium oxysporum suspension and then planted inside the hydroponic container. The plasma was irradiated to the roots in the nutrient solution; after cultivation, the incidence rate of wilt disease was inspected. It was observed that in case of plasma irradiation, the incidence rate reduced to less than 20 % within 5 min. This demonstrated the disease prevention efficacy by plasma irradiation. However, the incidence rate was found to be about 50 %, which was almost the same as that in the no-plasma condition, within 10 min of irradiation, and reached 90 % within 25 min of irradiation. Thus, plasma irradiation acts efficiently on the infected seedlings in solution with naturally rising temperature and exposure to ultraviolet light and some active radicals. These factors significantly contribute to the sterilization operation and may promote infection or disease prevention depending on the irradiation exposure time.