The effects of water deficits on fruit cracking and sunburn damage in ‘Cripps Pink’ apple

Apple growers in Australia are faced with extremely variable climates that can severely impact on fruit quality. Rainfall is arguably the most variable, causing a reduction in regional water resources for irrigation at one extreme and intense localized rainfall events at the other. Many apple orchards have adopted deficit irrigation strategies to cope with reduced irrigation allocation. Previous studies on the impact of deficit irrigation on apple fruit quality have mainly focused on soluble solids, color and fruit size with few studies on physical defects. The objective of this study was to investigate the effects of water deficits on sunburn damage and fruit cracking after intense summer rainfall events. Irrigation treatments were imposed over a 3-year period in a commercial 'Cripps Pink' apple (Malus domestica) orchard in the Goulburn Valley Region of Victoria, Australia. Treatments were 38, 50, 74, 100 and 162% of grower irrigation practice. Regular measurements of stem water potential showed that deficit irrigated trees were consistently water stressed in years 1 and 3. There were few differences in stem water potential between treatments in year 2 due to regular rainfall events. Sunburn necrosis tended to increase as stem water potential decreased but this only occurred in year 3 with approximately 4% of the harvested fruit in the 38% treatment showing sunburn necrosis. The effects of water deficits on fruit cracking were much more pronounced. Approximately two-thirds of the harvested fruit in the 38% treatment in years 1 and 3 were cracked. Water stress appeared to increase the susceptibility of fruit to cracking. Fruit cracking was partly attributed to a greater concentration of soluble solids that most likely increased turgor pressure following heavy rainfall leading to cracking of the skin at the calyx end.