Characterization of Parthenocarpic Fruit of ‘Miyazaki-wase No. 1’, a Tropical Squash (Cucurbita moschata L.) Cultivar

Parthenocarpy is a trait in which fruit set and development are induced without fertilization, thereby contributing to labor saving in fruit production. In Cucurbita species, parthenocarpic cultivars have been reported in Cucurbita pepo, but not in Cucurbita maxima and Cucurbita moschata. In this regard, the identification of parthenocarpic cultivars and clarification of their characteristics will contribute greatly to the research and breeding of the parthenocarpic trait in Cucurbita species. In this study, we aimed to genetically screen diverse Cucurbita accessions for high parthenocarpic ability and to elucidate the characteristics of the parthenocarpic cultivars discovered by the screening. We screened 33 accessions from squash genetic resources and found that a Cucurbita moschata cultivar, ‘Miyazaki-wase No. 1’, exhibited parthenocarpy. In order to clarify the characteristics, we examined the fruit set rate, fruit expansion, and fruit quality of ‘Miyazaki-wase No. 1’. In the spring and fall experiments, the fruit set rate of parthenocarpic fruit was lower than that of pollinated fruit. On the other hand, there was no significant difference in the transverse diameter and weight of parthenocarpic and pollinated fruits at harvest. These results indicated that the fruit set ability of parthenocarpic fruit is inferior to that of pollinated fruit, although the fruit expansion ability of parthenocarpic fruit was almost the same as that of pollinated fruit. In addition, we compared the composition of parthenocarpic fruit with that of pollinated fruit at harvest and after storage in the fall experiment. The results demonstrated that there was no significant difference in all the examined compositions between the parthenocarpic and pollinated fruits at harvest. On the other hand, the β-carotene concentration of parthenocarpic fruit was significantly lower than that of pollinated fruit one month and two months after harvest. These results indicated that parthenocarpic fruit development did not affect fruit quality at harvest, but had an effect on β-carotene metabolism during storage. We showed that ‘Miyazaki-wase No. 1’ is a parthenocarpic cultivar and clarified its characteristics. Based on the results, progress in research and breeding of parthenocarpic cultivars in Cucurbita species is anticipated in the future.