Description of Lignified Vascular Nodules in Fruit of `Gala' and Other Apple Cultivars

Abstract

Nodules associated with the main cortical vascular bundles in fruit of the `Gala' apple (Malus ×domestica Borkh.) strains `Royal' and `Regal' were observed in several growing seasons. The nodules were found in 68% (n = 586) of the fruits examined, with a mean of 2.5 nodules per fruit. The nodules were first detected in developing fruit 2 months after bloom and were normally 1-2 mm in diameter by commercial harvest maturity. The nodules, like the vascular bundles, were pale green. They were inconspicuous at first, but became conspicuous and unattractive and changed to brown or red as the fruit became overmature. Nodules in the fruit of the `Gala' × `Splendour' hybrid `8S 27-2' were dark brown or red at picking maturity, and occurred with high frequency. Nodules were also observed in `Splendour', but were small, pale green, and infrequent in this cultivar. Microscopic examination of the nodules revealed that they typically contained a central cavity surrounded by a lignified wall with small pigmented cells outside the wall adjacent to the cortex. Low-frequency irrigation cycle times generally promoted the development of nodules in both `Gala' strains but nitrogen treatments did not affect nodule frequency in `Royal Gala'. Mean fruit nodule frequency tended to be higher, overall, in `Regal Gala' (3.9) than in `Royal Gala' (1.4).