In Japan, one of the major problems in producing high quality blueberry fruit is that the harvesting season of many highbush blueberry cultivars occurs during the rainy season (June and July). For this reason, some growers are interested in forcing blueberries into producing mature fruit before the rainy season begins. In this study, many cultivars with a low chilling requirement, 'Bladen', 'Blue Ridge', 'Cape Fear', 'Cooper', 'Duplin', 'Flordablue', 'Georgiagem', 'Magnolia', 'Misty', 'O'Neal', 'Reveille', 'Sharpblue' and 'Summit' (southern highbush blueberry -SHb), 'Weymouth' (northern highbush -NHb) and 'Climax' (rabbiteye blueberry -Rb) controls were used. The flowering and harvesting time, fruit set, yield and fruit quality parameters were investigated. Potted 3 to 4-year-old old plants were transferred from outdoors into a plastic film greenhouse on 10 Feb. 2002 and 20 Jan. 2003 (used different plants each year). Temperature was maintained between 10 degrees C-35 degrees C with heating continued through 10 May each year. A small bee colony was provided for pollination during the flowering period. Both flowering and harvesting times were advanced 30-40 days under heated culture as compared to the natural environment. When comparing the cultivars, 20% of the total fruit yield was harvested earliest in 'Weymouth' during the last week of April, followed by 'Cooper', 'Blue Ridge', 'Reveille', 'O'Neal', 'Bladen', 'Misty', 'Flordablue', 'Georgiagem', and 'Sharpblue'. 'Climax' was the latest with 20% of yield harvested on the last week of June. Harvest of all cultivars except 'Climax' was completed by the last week of May (before the rainy season). Higher fruit set (over 75%, harvested fruit / flower) and higher fruit yield were obtained on 'Bladen', 'Blue Ridge', 'Cape Fear', 'Flordablue', 'Georgiagem', 'Reveille' and 'Sharpbluel. Fruit size was larger (over 2.0g per fruit at 20% harvest time) on 'Blue Ridge', 'Cooper', 'Magnolia', 'Misty' and 'Summit'than on 'Bladen', 'Reveille' and 'Climax'(under 1.4g).'Duplin', 'Georgiagem', 'Magnolia', 'O'Neal' and 'Climax' had higher soluble solids (over 12%) content. The highest concentration of citric acid, and lowest fruit pH was found in 'Blue Ridge'. Considering the harvest time, percent fruit set, yield, fruit size and taste, 'Blue Ridge', 'Flordablue', 'Georgiagem', 'Misty' and 'Sharpblue' southern highbush blueberry are recommended for forcing culture in Japan.
