カキ‘刀根早生’果実の流通中の熟柿化現象の原因究明と防止技術の開発

　Field grown ‘Tonewase’ Japanese persimmon had been cultivated as a leading persimmon variety in Wakayama Prefecture without any problem until 1993. Thereafter, however, a rapid fruit softening during postharvest distribution occurred and its rate increased every year coinciding with retardation of the temperature decrease in September which is the ripening season for the fruit. This produced a serious loss to the Prefecture. We clarified the mechanism of this fruit softening and developed a completely suppressible technique based on that mechanism. 　In ‘Tonewase’ persimmon fruit, water stress acted as a primary signal that triggered stress-ethylene production in the tissue of calyx through stimulating the expression of one of the ACC synthase genes, DK-ACS2, a stress responsible ethylene biosynthetic gene. This ethylene diffused into pulp tissue of the fruit, where transcription of DK-ACS1 for ripening-ethylene production was activaled through a positive feedback system, which in turn caused rapid fruit softening. 　This fruit softening derived from stress-ethylene was completely suppressed by packaging the fruit in perforated polyethylene bags or by using carton boxes laminated with a thin layer of plastic film. These techniques that alleviated water loss from fruit completely solved the rapid softening problem during postharvest distribution in ‘Tonewase’ fruit.