Influences of gibberellins A4, A4+7, and A4+iso—A7on apple fruit quality and tree productivity. I. Effects on fruit russet and tree yield components

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Abstract
Mature ‘Golden Delicious’ apple trees in British Columbia (B.C.) and Québec, Canada and Cox’s Orange Pippin apple in Canterbury, New Zealand were sprayed weekly for four weeks, commencing at petal fall, with formulations of GA4, GA4+7 mixture (1:1) or GA4+iso—GA7 (a less active isomer). This study was predicated on previous work suggesting that GA4 is more effective than GA7 for fruit russet control and is less likely than GA7 to inhibit return flowering. It was hypothesized that conversion of GA7 in the GA4+7 mixture to iso—GA7 might ameliorate the expected negative effect of the GA treatment on return flowering. Surface russet was prevalent on Québec ‘Golden Delicious’ and all GA treatments reduced its severity. Stem-end russet was reduced by GA4+iso—GA7 in the B.C. ‘Golden Delicious’ trial but none of the treatments influenced stem-end russet of New Zealand ‘Cox’s Orange Pippin’. All G As and GA mixtures reduced fruit set and seed number per fruit and increased average fruit weight in one or more experiments. There were clear indications that iso—GA7 does have biological activity, at least when applied with GA4. Most importantly, return flowering of ‘Cox’s Orange Pippin’ was less adversely affected by GA4+iso—GA7 than by the original GA4+7 mixture. GA4 (7.5 mg T1) promoted return flowering of ‘Golden Delicious’ in British Columbia whereas 15 mg/l/GA4+7, GA4+iso—GA7 and GA4 were ineffective.

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