Abstract
We studied the effects of water stress from summer until harvest time on the fruit quality of the medium-late maturing citrus cultivar ‘Harehime,’ [(‘Kiyomi’ × ‘Osceola’) × ‘Miyagawa wase’]. During the dry treatment, we induced water stress of −0.7 to −1.2 MPa leaf water potential (φmax) from mid August until harvest time. We did not induce water stress using wet treatment. Following dry treatment, the Brix value of the fruit juice at harvest time was about 3 degrees higher than that following wet treatment, and the fruit lateral diameter decreased to about 1.3 mm. In particular, since the Brix value following these two treatments differed by 2.9 degrees by the beginning of October, water stress from August to September probably has a large effect on the increase in Brix of the fruit. Regarding the fruit quality at harvest time following the dry treatment, the fruit weight was about 10% lower than that following the wet treatment, and the reddish color of the fruit epicarp became darker. There was no difference in the sugar component ratios of the fruit juice following these treatments, but after the dry treatment, fruit had about 1.6 times higher total sugar content than those after the wet treatment. Regarding organic acids in the fruit juice, the citric acid content after the dry treatment was 1.3 times that after the wet treatment, and the malic acid content after the dry treatment was about 0.7 times that after the wet treatment. The content of 9 amino acids in the fruit juice was higher after the dry treatment than that after the wet treatment. Furthermore, the dry treatment achieved increases of about 3 times as much aspartic acid and about 2.1 times as much glutamic acid compared to those after the wet treatment. The total amino acid content after the dry treatment was about 1.7 times that after the wet treatment. These findings suggest that water stress after summer causes the fruit to be somewhat smaller, but makes its juice components more concentrated, thereby enabling the production of a highly marketable fruit.
