Polyamines dynamics in buds and flowers in response to fall foliar fertilisation in ‘Hayward’ kiwifruit

The present study aimed to optimise a fertiliser combination and find the effective timing for foliar fertilisation in the fall to determine whether the application of N, B and Zn fertilisers can improve fruit set and alter endogenous polyamines. 'Hayward' Kiwi vines were sprayed with CO(NH2)2 (urea), H3BO3 and ZnSO4 (alone and in combination) on different dates (September 17, October 7 and October 28). Buds were sampled at three stages (before dormancy, during dormancy and full bloom) to determine endogenous polyamines content. In the following growing season, bud break, percentage of flowering shoots and effective pollination period (EPP) were determined. Our results showed CO(NH2)2: H3BO3: ZnSO4 (10, 1.5 and 2 g l−1 respectively) on October 28 was the best fertiliser combination and application time. This treatment significantly increased putrescine, spermine and spermidine accumulation in bud and flower tissues, as well as bud break and flowering. In vines treated with this combination on October 28, EPP was at least 2 days longer than control. The foliar fertiliser treatment applied the previous fall increased fruit set to 83% (absolute). This improvement was associated with an increased accumulation of endogenous polyamines in bud and flower tissues.