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

Abstract

<jats:p>Nodules associated with the main cortical vascular bundles in fruit of the `Gala' apple (<jats:italic>Malus</jats:italic> ×<jats:italic>domestica</jats:italic> 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).</jats:p>

Frequency of Vascular Nodules in the Fruit of 'Gala' × 'Splendour' Hybrids and Other Apple Cultivars

“…'Royal Gala , a strain of 'Gala , had a mean nodule frequency similar to 'Gala , 1.6 nodules per fruit. These data are similar to frequencies reported by Lane et al (2000) for 'Royal Gala but less than the values reported for 'Regal Gala of 3.6 to 8.4.…”

“…This suggests other factors may influence genetic expression. Lane et al (2000) reported that deficit irrigation promoted nodule frequency with 'Royal Gala and 'Regal Gala cultivars in British Columbia, but different nitrogen nutrition levels had no effect. Unpublished reports focusing on environmental causes of nodulation in cultivar NZ 2085, 'Sciros ™, in New Zealand found tree size, fruit exposure to light or shade, crop load, or position on canopy did not correlate with nodule frequency.…”

“…Their presence in the hybrids and in both parents at low frequency, but not in most other cultivars, suggested a genetic predisposition to nodule development. Nitrogen nutrition, geographical location, fruit position within the tree, tree age, and endophytic bacteria in the cortex and nodules did not explain the presence of the nodules, although deficit irrigation was reported to promote nodule frequency in 'Gala (Lane et al, 2000).…”

“…Size distribution was from very small, barely detectable nodules to the largest, or several fused nodules, up to 8 mm long. The shape, orientation, and size of the nodules has been described previously (Lane et al, 2000).…”

“…The frequent occurrence of small green vascular nodules consisting of aggregations of small cells, often with a lignified central cavity, in the cortex of 'Gala x 'Splendour hybrids was reported by Lane et al (2000). Their presence in the hybrids and in both parents at low frequency, but not in most other cultivars, suggested a genetic predisposition to nodule development.…”