HORTSCIENCE, V OL. 38(3), JUNE 2003 422 POSTHARVEST BIOLOGY & T ECHNOLOGY Frequency of Vascular Nodules in the Fruit of ‘Gala x ‘Splendour Hybrids and Other Apple Cultivars Ian McIvor 1 and Alexander Lang HortResearch, Private Bag 11–030, Palmerston North, New Zealand W. David Lane Pacific Agri-Food Research Centre, Agriculture and Agri-Food Canada, Summerland, British Columbia, V0H 1Z0, Canada Paula E. Jameson Institute of Molecular BioSciences, Massey University, Private Bag 11–222, Palmerston North, New Zealand Additional index words. Malus ×domestica, breeding, recessive gene, hybrids, cultivar, fruit quality Abstract. The new apple (Malus ×domestica Borkh.) cultivar Sciros , resulting from a cross of ‘Gala with ‘Splendour , is marketed internationally from New Zealand. A characteristic of this cultivar is the presence of dense, dark green or black nodules in the fruit cortex, located in close proximity to the five sepal vascular bundles. Nodules are visible as green spots beginning about 40 days after bloom and they continue to develop, reaching a length of up to 8 mm at fruit maturity, although there is considerable variation in their size. Large vascular nodules often develop dark brown centers and reduce the visual quality of the fruit flesh. The frequencies of vascular nodules in 61 ‘Gala x ‘Splendour hybrids from New Zealand and British Columbia, Canada, were examined. These ranged from a mean of 0 to 12.1, depending on the hybrid. Thirteen hybrids were in the high frequency class (2.76–12.1), 28 in the low frequency (0.04–1.86), and 20 were without nodules. The mean nodule frequency in Sciros TM was 12.1 nodules per fruit, the highest of all hybrids examined. Our survey of 44 other cultivars confirmed the occurrence of vascular nodules in ‘Gala and ‘Splendour , with mean vascular nodule frequency of 1.9 and 0.5 nodules per fruit, respectively. Nodules were also found in ‘Newtown Pippin (frequency 0.8), and in a ‘Newtown Pippin x ‘Granny Smith hybrid (frequency 0.1). 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 par- ents 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 pres- ence of the nodules, although deficit irrigation was reported to promote nodule frequency in ‘Gala (Lane et al., 2000). Vascular nodules in apple fruit cortex are closely associated with the large vascular bundles, and they increase in size and change color from pale green to dark green or black and sometimes red during growth and develop- ment. As vascular nodules enlarge in mature fruit, the center of the nodules often becomes brown. This appears to be the result of the death of some of the cells in the central part of the nodule and formation of a lignin shell. When the nodule is bisected, a brown central cavity surrounded by lignin is apparent. The nodules are not conspicuous in freshly picked fruit, but they become more noticeable after storage and the appeal of the fruit to the con- sumer is reduced, especially if the fruit is sliced longitudinally. Our report details the presence or absence and frequency of vascular nodules in 61 ‘Gala x ‘Splendour hybrids originating and grown in both New Zealand and British Columbia, Canada. In addition, 44 apple cultivars, includ- ing ‘Gala and ‘Splendour , grown in one or both locations were examined for nodules. We provide further information on the vascular nodule frequency distribution of ‘Gala x ‘Splendour breeding selections. Materials and Methods Apples (Malus ×domestica Borkh.) used in this investigation were from samples col- lected from the repository orchard located at the HortResearch Hawkes Bay Research Centre at Havelock North, Hawkes Bay, New Zealand, and from breeding and cultivar plots at the Pa- cific Agri-Food Research Centre, Summerland, British Columbia, Canada. At Hawkes Bay, fruit of 41 ‘Gala x ‘Splendour hybrids were picked from 13-year-old trees. This fruit was stored at 1 °C and nodules examined within 3 weeks of picking. The Summerland fruit was from trees 7–9 years old of 20 ‘Gala x ‘Splendour hybrids. This fruit was stored at 5 °C and examined within 5 d of picking. Several of the ‘Gala x ‘Splendour hybrids have been released as named cultivars (Table 1). Sample sizes were 25 fruit for the fruit collected at Hawkes Bay and a lesser number (indicated in Table 1) for some Summerland samples. In addition to the ‘Gala x ‘Splendour hy- brids, fruit of 29 cultivars (‘Albany Beauty , ‘Braeburn , ‘Coromandel Red , ‘Count Oratia , ‘Cox s Orange Pippin , ‘Delicious , ‘Democrat , ‘Early Red , ‘Ellison s Orange , ‘Emergo , ‘Fiesta , ‘Fuji , ‘Gala , ‘Golden Harvest , ‘Golden Delicious , ‘Granny Smith , ‘Hawkes Bay Red , ‘Jonalicious , ‘Kidd s Orange , ‘Northern Spy , ‘Oregon Spur , ‘Red Dougherty , ‘Rome Beauty , ‘Shizuka , ‘Spartan , ‘Splendour , ‘Stur- mer , ‘Summerland , and ‘Newton Pippin ) were collected from the Hawkes Bay cultivar repository orchard. At Summerland, fruit of 15 additional cultivars (‘Belle De Boskoop , ‘Discovery , ‘Elstra , ‘Empire , ‘Garland , ‘Gloster , ‘Gravenstein , ‘Idared , ‘Jester , ‘Jonadel , ‘Jonathan , ‘McIntosh , ‘Mutsu , ‘SummerRed , and ‘Tydeman s) and a ‘New- ton Pippin x ‘Granny Smith hybrid (8C-31- 110) were collected and examined. Fruit of the named cultivars were stored and examined in the same way as the ‘Gala x ‘Splendour hybrids. The technique used to count the vascular nodules in individual apples was based on pre- liminary experiments that established that the nodules were most frequently associated with the sepal and, to a much lesser extent, the petal vascular bundles within the apple flesh. The sepal vascular bundles can be seen opposite the locules in apples cut laterally. Frequency of nodules associated with the sepal bundles was 12 times greater than with petal bundles. Therefore, only vascular nodules associated with the sepal bundle were recorded. Nod- ules do occasionally appear in the cortex, away from the large sepal and petal vascular bundles, but their frequency was less than 1% of the sepal bundle-associated vascular nodules. To determine nodule frequency, the apple fruit was cut in half laterally using a thin, sharp knife. Each half of the fruit was then cut longi- tudinally into five sections with the cut made alongside the sepal bundle. The nodules were much darker in color than the cortex and were easily seen even if the cut was not in exact alignment with the sepal bundle. Nodules were counted in initial experiments using a stereo microscope, but this was later found to be unnecessary as we became more practised at identifying the nodules. Since nodules were frequently bisected when sectioning the fruit, the cut surfaces were matched to avoid counting a nodule twice. The number and location of nodules were recorded for each fruit. HORTSCIENCE 38(3):422–423. 2003. Received for publication 30 April 2002. Accepted for publication 19 July 2002. I. McIvor was funded by a Royal Society of New Zealand Teacher Fel- lowship. 1 To whom reprint requests should be sent. E-mail address: imcivor@hortresearch.co.nz