Delayed chilling appears to counteract flowering advances of apricot in southern UK

Temperatures are rising across the globe, and the UK is no exception. Spring phenology of perennial fruitcrops is to a large extent determined by temperature during effective chilling (endo-dormancy) and heataccumulation (eco-dormancy) periods. We used the apricot flowering records of the UK National FruitCollections (NFC) to determine the influence of temperature trends over recent decades (1960–2014) onapricot (Prunus armeniaca L.) flowering time. Using Partial Least Squares (PLS) regression, we determinedthe respective periods for calculating chill and heat accumulation.Results suggested intervals between September 27th and February 26th and between December 31stand April 12th as the effective chilling and warming periods, respectively. Flowering time was corre-lated with temperature during both periods, with warming during chilling corresponding to floweringdelays by 4.82 dC1, while warming during heat accumulation was associated with bloom advancesby 9.85 dC1. Heat accumulation started after accumulating 62.7 ± 5.6 Chill Portions, and floweringoccurred after a further 3744 ± 1538 Growing Degree Hours (above a base temperature of 4C, with opti-mal growth at 26C). When examining the time series, the increase in temperature during the chillingperiod did not appear to decrease overall chill accumulation during the chilling period but to delay theonset of chill accumulation and the completion of the average chill accumulation necessary to start heataccumulation. The resulting delay in heat responsiveness appeared to weaken the phenology-advancingeffect of spring warming. These processes may explain why apricot flowering time remained relativelyunchanged despite significant temperature increases. A consequence of this may be a reduction of frostrisk for early flowering crops such as apricot in the UK.

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DOI:

https://doi.org/10.1016/j.agrformet.2017.02.017

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