A shortage of seedlings of Peucedanum japonicum Thunb. var. latifolium M.Hotta et Shiuchi in Minamisatsuma city of Kagoshima prefecture has become a serious problem recently because P. japonicum plants are popular as a healthy vegetable in islands of Kagoshima and Okinawa prefecture. In our interview with farmers and research, the reason for it was a low germination percentage of P. japonicum var. latifolium. The objective of our research was to clarify the temperature which increased germination percentages. One hundred seeds were put in 9 cm-diameter petri dishes with 10 mL distilled water, dishes were tested in 24hrs dark conditions in incubators. We also compared the germination of seeds with decortication and control treatments. In 24hrs constant temperature treatments (20, 25, and 30℃), about 40% of germination percentages were observed at 25℃ with decortication, and lower germination percentages were at 20℃. No germination was observed at 30℃. In 12/12hrs alternative temperature treatments(10/25℃, 20/25℃, 20/30℃, and 25/30℃), seeds could not germinate at 10/25℃, 20/30℃ and 25/30℃, and control at 20/25℃ treatments showed about 10% germination percentages, while decortication treatments at 15/20℃, 15/25℃ showed more than 20%, and more than 40% at 20/25℃, especially. Therefore, it was estimated that daily changes of temperature could affect germination severely, and for the increase of germination percentages, the temperature has to be adjusted 20/25℃ and it will be better with decortication.

In this study, we investigated the effect of rootstocks on leaf fall during winter, tree growth, fruit yield and quality in young tankan ‘Tarumizu 1’ trees. For the rootstock, Carrizo citrange (Citrus sinensis Ocb. × Poncirus trifoliata Raf., CC), Satsuma kikoku (Citrus neo-aurantium Hort, SK), Swingle citrumelo (Citrus paradisi × Poncirus trifoliata Raf., SC) and Trifoliate orange (Poncirus trifoliata Raf., TO) were used. The leaf fall during winter was lower in the CC, SK and SC than in the TO. The spring shoot length and the spring leaf area tended to be larger in the CC, SK and SC than in the TO. When the tree was 8 years old, the canopy volume tended to be larger and the yield tended to be higher in the SK and SC than in the TO. Compared to the TO, the CC, SK and SC had higher average fruit weights and higher proportions of L and 2L class fruits. The brix tended to be lower in the CC, SK and SC than in the TO, but in 2017 it exceeded 11° in the CC and SC. In conclusion, the leaf fall during winter was improved on the CC, SK and SC. In addition, the characteristics of each rootstock in young trees were clarified, such as the tendency that the growth and yield of these rootstocks were superior to those of the TO.

Three sugarcane cultivars were planted in spring and summer under uncontrollable meteorological disasters, such as droughts and typhoons, and monitored for eight years, each to the first ratooning. Available sugar yields (ASY) and their components affected by meteorological disasters, crop types and cultivars were analyzed, and factors for improving sugar yields in cultivation systems were investigated. Although ASY and its components fluctuated greatly due to droughts and typhoons, effects of crop types and cultivars were also clear. Regarding the stability of components, the available sugar content was the most stable, and the millable cane number slightly stable. However, the millable cane weight and ASY decreased because the stalk weight was affected by drought during the vigorous growing season. Therefore, it was suggested that the stalk weight has great potential to stably increase ASY by improving soil water retention and irrigation during the growing season. The annual ASY was significantly higher in the order: spring planting ratooning system, summer planting ratooning system, and summer planting system. However, cultivation systems should be flexibly selected according to farm scale and labor force. In addition, it is important to select a high-sugar cultivar with heavy stem and high ratoon-ability, and improve fertilization method to stabilize the sugar yield of the summer planting ratooning. New cultivar RK97-14 is recommendable higher ASY in all cultivation systems; however, it is more suitable for a little late summer planting as it is easy to lodge.