Abstract/Summary

A field facility was developed to study the impact of climate change on apple (Malus domestica Borkh.) production comprising 14 contrasting varieties in an experimental orchard covered by polythene tunnels in 2017 (ambient environment initially). In 2018 and 2019, vents were manipulated automatically to modify temperature (ambient, up to +2°C, or up to +4°C) and rainfall was redistributed by irrigation (ambient, -20%, or +20%). The irrigation treatments had little or no effect. Phenology (bud break, flowering, petal fall, fruit maturity) was affected by variety and temperature, with fruit maturity date ranging from 4th July (“Starks Earliest”, warmest regime, 2018) and 24th October (“Lappio”, ambient, 2017). The response of rate of development to temperature combined across years (2017-19) and different temperature regimes (2018-19) was analysed successfully using thermal time approaches. Contrasting responses were detected amongst varieties and for different phenological phases. Maximum net photosynthetic rate varied amongst the six apple varieties studied, and all six declined progressively with an increase in temperature. Vegetative growth (assessed by trunk circumference growth, shoot extension, and tree pruning weight) was often affected by mean temperature, usually positively, but varieties differed considerably with some inconsistency between years. Biennial bearing was evident with reduced flowering and fruit yield in 2018; certain varieties were more affected than others. There was considerable variation in the sensitivity of fruit yield to temperature across the 14 varieties: in the culinary variety Bramley’s Seedling at warmer temperatures reduced fruit yield, reduced fruit number and increased mean fruit weight in both years; at the other extreme Edward VII (culinary variety) showed no detectible sensitivity of yield or yield components to temperature in either year (thus the most resilient variety to environmental change). Future warmer temperatures have the potential to reduce UK apple production, but adaptation through the selection of resilient varieties is a viable solution.