Temperature and irrigation effects on the cropping, development and quality of `Cox's Orange Pippin' and `Queen Cox' apples

Abstract

The cropping and growth of apple fruit of `Cox's Orange Pippin' and `Queen Cox' trees was investigated in relation to temperature and irrigation in an orchard at East Malling in Kent, UK. The air temperature surrounding a block of orchard trees was elevated by enclosing in a polythene tunnel from bloom in May until harvest in early September; throughout this period the trees were irrigated. A second block of trees was covered partially with a polythene tunnel, with the intention of providing a similar light regime as in the complete polytunnel, but without raising the temperature. To examine the effects of irrigation, some trees outside the polytunnels received irrigation while others did not. Detailed continuous measurements of the canopy climate, particularly temperature, were made until harvest. Throughout the growing season, fruit size was measured repeatedly and non-destructively to calculate fruit volume and fruit growth rates. The largest `Cox' and `Queen Cox' fruits were obtained from the trees grown in the complete polytunnel with irrigation, where the higher temperature was associated with fewer fruit being retained and the individual fruit growing more than those at the lower temperature. Fruit on trees in the partial tunnel with irrigation, and outside with irrigation, were similar in size. The smallest fruit were produced on the non-irrigated trees outside. The mean cortical cell area of the `Cox' fruit from non-irrigated trees outside was not significantly smaller than that from either the outside irrigated (OI) or the polytunnel-grown (PT) fruits: despite this, differences in cell area, rather than cell number, were a more likely explanation for the effects of temperature or irrigation on final fruit size. The increases in fruit size were associated with a greater loss of fruit texture and quality during storage than in smaller fruit from non-irrigated trees.