Selection of prune (Prunus domestica L.) cultivars suitable for the East Asian temperate monsoon climate: Ripening characteristics and fruit qualities of certain prunes in a warm southwest region of Japan

Prune trees (Prunus domestica L.) are optimally suited to dry climates, and a major production area for prune trees is California, which has little rainfall. The East Asian temperate monsoon zone, where summer is hot and rainfall is relatively abundant, is not well suited for cultivating prune trees. The purpose of this study was to investigate prune cultivars that are ideal for this temperate monsoon zone to expand the possibility of production. We evaluated the performance of 8 prune cultivars, ‘Puchull’, ‘Purple Ais’, ‘Blue Tan’, ‘Edwards’, ‘Stanley’, ‘Valor’, ‘President’, and ‘Marjorie’s Seedling’, by harvesting fruits from August to October to identify optimal cultivars in Izumo, western Japan, as a model area in the temperate climate monsoon zone. Results showed that the flowering period of prune trees was from late March to mid-April, and average temperature in March influenced whether flowering time would occur early or late. The flowering period varied by year. Therefore, companion planting with other cultivars that have overlapping flowering periods is necessary for self-incompatible cultivars. To avoid spring frost damage during the flowering period, protection from frost was necessary. Additionally, to avoid fruit cracking, cultivating prune trees under rain shelter conditions was also necessary. With these management approaches, two mid-ripening types, ‘Stanley’ and ‘Valor’, and two late-ripening types, ‘President’ and ‘Marjorie’s Seedling’, yielded over 1000 kg/10 a/canopy area and produced high-quality fruit with over 20 soluble solids content (SSC)/titratable acid (TA). However, three early-ripening types, ‘Puchull’, ‘Purple Ais’, and ‘Blue Tan’, and the mid-ripening ‘Edwards’, showed relatively low yields and produced fruit with low SSC/TA. Moreover, flesh darkening before harvest was observed as a result of high-temperature injury in these cultivars, and skin color and fruit taste were not good enough before flesh darkening; thus, these four cultivars were not suitable for table use. In summary, we consider mid- to late-ripening cultivars suitable for table use in Izumo. Our findings also indicate the possibility that these prune fruit cultivation methods could be used in other parts of the East Asian temperate monsoon and humid temperate climate zone.