DEVELOPING LOW CHILL, HIGH QUALITY JAPANESE PLUMS IN SUBTROPICAL TAIWAN

Taiwan, situated on the western edge of the Pacific Ocean, is transversed by the Tropic of Cancer and has a summer rainy season in a subtropical climate with a warm winter—the limiting factor for producing traditional temperate zone deciduous fruits. Growing deciduous fruit on the slopes at high elevations led to water erosion of soil, and as an alternative, the Taiwan Government in 1980, encouraged the breeding of low chill unit (cu) cultivars to be planted on less erodeable slopes at lower elevations. Only 35 ha of standard high chill plum (Prunus salicina Lindl.) cultivars are planted in limited mountain areas above 1500 m elevation. The planted area of Japanese plums in Taiwan was 9150 ha in 1990, but decreased to 4569 ha by 2000, primarily due to small fruit size and low fruit quality of the low chill local cultivars which do not compete on modern fruit markets. The main objective in plum breeding was to develop low chill cultivars with high fruit quality. Twenty-five native low-chill plums collected throughout Taiwan and 11 introduced from the University of Florida were evaluated at the Rona repository for tree and fruit characteristics. Three of the evaluated genotypes are recommended for grower trial. Four sweet skin genotypes were selected from local germplasm as breeding parents. Five genotypes with good eating fruit quality and a low chill requirement, selected in the breeding program, are in early commercial production.

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