Effects of water deficits on FST, fruit surface temperature, and sunburn damage in apple ?Cripps Pink?

Apple production systems in Australia are geared to supply the best quality fruit so that domestic consumption is sustained and export markets can expand. Growers, however, are faced with extreme variability in rainfall that can severely reduce regional irrigation resources. Many apple orchards are adopting deficit irrigation strategies to cope with reduced irrigation allocation. The objective of this study was to investigate effects of water deficits on fruit surface temperature (FST) and sunburn damage. Irrigation treatments were imposed 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 applied from bud burst to leaf fall. Measurements of stem water potential showed that the 38 ? 100% trees were water stressed compared to the 162% trees and this resulted in a reduction in yield and fruit size. Sunburn damage was determined at harvest by separating and counting fruit that visually showed oxidative, browning and necrotic damage. There was no treatment difference in the number of fruit with oxidative and browning damage. Sunburn necrosis tended to increase with water deficit. Approximately 4% of the harvested fruit in the 38% treatment had sunburn necrosis. Observations of FST were made in the 38 and 162 % treatments. Fine-wire copper-constantan thermocouples were inserted just under the skin on the top surface of fruit exposed to direct solar radiation. FST was up to 10?C above ambient temperature but there was no difference in FST of trees irrigated at 38 and 162%. Based on these results, there was no evidence that water deficits increased FST. The increase in sunburn necrosis may have been associated with an increase in the number of fruit exposed to direct solar radiation from less vegetative growth.SourcesThe effects of water deficits on fruit surface temperature and sunburn damage in Cripps Pink appleDr. Ian Goodwin, Research Manager, Agriculture Victoria, Private Mailbag 1, Tatura, VIC 3616, Australia; ian.goodwin@ecodev.vic.gov.au (presenting author)Dr. Des Whitfield, Private Mailbag 1, Tatura Victoria 3616, Australia; des.whitfield@ecodev.vic.gov.au (co-author)Dr. Mark O'Connell, Private Mailbag 1, Tatura Victoria 3616, Australia; mark.oconnell@ecodev.vic.gov.au (co-author)Dr. Steve Green, Private Mailbag 11600, 4442 Palmerston North, New Zealand; steve.green@plantandfood.co.nz (co-author)ICH2018 Istanbul, 30th International Horticultural Congress, 12-16 August 2018, TurkeyPicture: Research Gate -?Three types of Sunburn (from left to right): Sunburn Necrosis, Sunburn Browning, and Type 3 Sunburn