Effects of Elevated Spring Temperatures on the Growth and Fruit Quality of the Mandarin Hybrid 'Shiranuhi'

The effects of elevated spring temperatures on the growth and fruit quality of the mandarin hybrid 'Shiranuhi' [(Citrus unshiu x C. sinensis) X C. reticulata] were investigated in plastic greenhouses, to develop a cropping system to improve the quality of the fruit and increase the income of growers on Jeju Island, South Korea. Under conditions of elevated temperature I (25/15 degrees C, day/night) and elevated temperature II (28/18 degrees C, day/night) during early spring, budburst was advanced by 11 and 15 d, and full bloom by 22 and 45 d, respectively, compared to those of the plants grown at ambient air temperature in a plastic greenhouse. Elevated temperatures decreased the number of spring shoots but increased mean spring shoot length and leaf area. Growing 'Shiranuhi' trees at elevated temperatures resulted in increases in mean fruit weight and fruit L/D ratio (> 1.0). In addition, fruit color development was significantly advanced in trees grown under elevated temperatures during early spring which allowed the fruit to be harvested 1-2 months earlier than trees grown under ambient air temperature. Fruit soluble solids content (SSC) and titratable acidity (TA) at harvest were similar between elevated temperature I and ambient air temperature, but were significantly higher than at elevated temperature II. Considering fruit quality, harvest time, and yield, the elevated temperature treatment regime of 25/15 degrees C (day/night) during early spring could be useful for cultivation of the mandarin hybrid 'Shiranuhi' to increase the income of growers.