Blackheart in a Tender Apple Cultivar is Not Influenced by Using a Hardy Frame

in HortScience

To determine the effects of rootstock and frameworking on hardiness, `Gravenstein' apple, which is not winter hardy, was grafted on trees frameworked with the hardy genotypes `Budagovsky 9' (B. 9), `Lobo', Kentville Stock Clone (KSC 28), or `Dudley', all of which were propagated on either `Beautiful Arcade' (BA) seedlings or on `Alnarp 2' (A. 2) rootstocks. For comparison, `Dudley' was grafted on `Dudley' frames propagated on both rootstocks. Growth after 8 years was greatest at Kentville; `Gravenstein' was larger than `Dudley', although when grafted, it was 40% smaller on the dwarf B. 9 than on the `Lobo' frame. On one night in Feb. 1993, all sites recorded temperatures below –30 °C. Blackheart was therefore measured in the rootstock trunk, framebuilder, and scion to document the resistance to this sublethal winter injury. Trees at the two colder sites, Truro and Centreville, had more blackheart than did those at the milder site. The percentage of blackheart in the trunk and frame was greatest for B. 9 and least for KSC 28. The tender scion, `Gravenstein', exhibited extensive blackheart regardless of site, rootstock, or the hardiness of the frame. The hardy scion, `Dudley', had some blackheart in the colder locations but none at Kentville. Blackheart levels in `Gravenstein' were very high on the framebuilder B. 9, and while generally less with the other hardy framebuilders, they were still high. While the hardy frames may have helped improve the survival of this cultivar, they did not change its hardiness status relative to `Dudley', even when `Dudley' was one of the hardy framebuilders.

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