Fruit Setting and Quality of ‘Koyama New Summer’ Covered with Cheesecloth during the Flowering Period

Abstract

‘Koyama New Summer’ is a bud mutation of ‘Hyuganatsu’ (Citrus tamurana hort. ex Tanaka), which has highly parthenocarpic traits compared with ‘Hyuganatsu’. We investigated fruit setting and quality of ‘Koyama New Summer’ and ‘Hyuganatsu’ that had been covered with cheesecloth during the flowering period. The number of ‘Koyama New Summer’ fruits harvested per area occupied by tree crowns was larger than that for ‘Hyuganatsu’. It was considered that the factor determining the larger number of fruits in ‘Koyama New Summer’ was the fact that there were more leafless fruits than in ‘Hyuganatsu’. It was considered that ‘Koyama New Summer’ is capable of achieving sufficient fruit setting through parthenocarpic traits alone. In addition, the pulp ratio per fruit of ‘Koyama New Summer’ was larger than that of ‘Hyuganatsu’, and in the case of peeling by hand, its edible portion is larger than ‘Hyuganatsu’. Using decision tree analysis to clarify factors determining the high fruit quality (defined as fruits with a large diameter, high Brix, and low acidity), the results showed that height above the ground should be >142.5 cm, the fruiting mother shoot length should be >12.25 cm, and the number of leaves on the fruit-bearing shoot should be >0.5. The results indicate the importance of maintaining an optimal sunlight environment and strong tree vigor for producing high-quality fruits of ‘Koyama New Summer’.