2019 年 88 巻 2 号 p. 253-262
Bitterness, caused by cucurbitacins, is present in some melon fruit. Although bitter compound biosynthesis and regulation in Cucurbitaceae plants have been reported, the dynamic changes in bitterness during fruit development are unknown. Bitterness severity was measured for 19 inbred melon lines, including 14 lines of Cucumis melo var. chinensis, two var. inodorus and three var. conomon, using a panel tasting method. The data showed that bitterness severity was different in several lines of var. chinensis during fruit growth and maturation. Nb46 and Nb320, two elite parental lines of var. chinensis used in melon breeding, were used as experimental materials. Bitterness was severe at stage I, but moderate and disappeared at stage II and III in the fruit of Nb46. There was non-bitterness in the fruit of Nb320 throughout the development period. Furthermore, the cucurbitacin B (CuB) content gradually decreased in Nb46, while in Nb320, the CuB content changed little and remained at a quite low level during fruit development. Different expression patterns of the genes involved in CuB biosynthesis and regulation were found between Nb46 and Nb320. The expression levels of these genes were significantly higher in Nb46 than Nb320 in the early developmental stages, and this correlated with a higher concentration of CuB in Nb46 than Nb320. These results demonstrate that bitterness severity is different in var. chinensis during fruit developmental stages, and that the CuB biosynthesis-related genes are a critical factor in this process. We hope these findings will contribute to the breeding of non-bitter melon cultivars.
