The Relationship Between Oil Gland and Fruit Development in Washington Navel Orange (Citrus sinensis L. Osbeck)

Changes in structure, size and number of oil glands located in the fruit rind were assessed in developing fruit of the Washington Navel orange ( Citrus sinensis L. Osbeck) from pre-anthesis to fruit maturity. Initiation of oil glands was found to be restricted to early fruit development. Glands continued to develop throughout fruit growth, until all reached maturity by a fruit size of 30 to 50 mm diameter. Mature glands continued to enlarge with fruit growth. Mature fruit had between 8 000 and 12 000 oil glands. Anatomical studies of the fruit rind were carried out using light microscopy on samples prepared by different tissue processing methods. Glands were found to develop from a cluster of cells adjacent to the fruit epidermis, into a structure consisting of a central cavity surrounded by several layers of epithelial cells. All glands were joined to the fruit epidermis, irrespective of their stage of development. Neither lignin nor suberin was present in the gland. Gland cavity formation appeared to involve schizogeny.