Evaluation of Blueberry Types and Cultivars for Early Market Production in Japan Using Unheated Plastic House Culture

The purpose of this study was to evaluate the adaptability of blueberry types and cultivars to produce ripe fruit before Japan's rainy season (June and July) in unheated plastic house culture. The flowering and harvesting time, fruit growing interval, and fruit quality parameters of northern and southern highbush and rabbiteye blueberries cultivars were tested. Three-or four-year-old potted plants grown outdoors were brought into an unheated plastic house on February 10, 2008 (experiment 1) and 2009 (experiment 2). Standard watering, fertilizing, and bee pollination methods were used. In experiment 2, the average temperature of air and pot soil in the unheated plastic house was higher than that of the open culture. Flowering time was about 26-40 days earlier, and ripening time was about 7-40 days earlier in an unheated plastic house culture compared to an open culture. This resulted in 80% of all southern highbush and some northern highbush cultivars being almost completely harvested before the rainy season began (the beginning of June). Harvest time for rabbiteye cultivars, however, extended into the rainy season. The fruit growing period (days from 50% flowering time to 50% harvesting time) of all three types of blueberries in the unheated plastic house culture were longer than that in the open culture. Fruit size, soluble solid content, and citric acid content, soluble solid content/citric acid content ratio differed among cultivars. On the whole, soluble solid and citric acid content of all cultivars grown under an unheated plastic house culture were lower than that of fruit grown in an open culture.