Integrated effects of harvest timing, cooling regimes and controlled atmosphere on internal breakdown disorders of ‘Gem’ pears

Abstract ‘Gem’ pear ( Pyrus communis L.) is a relatively new European winter pear cultivar with good fire blight resistance. In research settings, ‘Gem’ can be stored in air for 5 months and in controlled atmosphere (CA) for 8 months with good quality retention, but commercial ‘Gem’ storage has proven more challenging, primarily due to an internal flesh (cortex) physiological disorder termed internal breakdown and/or internal browning, with symptoms including lens-shaped cavities in the flesh similar to those found in CA-related disorders. In the present study, results indicate that management strategies associated with lower internal breakdown and/or internal browning incidence include rapid and complete cooling of fruit after harvest followed by air storage at −1.1°C or delaying CA (1.25 kPa O 2 , <0.1 kPa CO 2 ) until fruit are thoroughly cooled. Fruit weight less than 248 g was also linked to reduced disorder incidence. Conditions where fruit cooling is delayed (simulating slower completion of thorough cooling in commercial settings), CA establishment is rapid (1 day after harvest), or CA CO 2 levels are high (5 kPa CO 2 ), along with larger fruit weight (greater than 248 g) were associated with higher internal disorder incidence. Significance of the study What was already known about this subject? Previously published research on the new pear cultivar ‘Gem’ revealed an internal breakdown/browning disorder that worsened with prolonged storage, indicating a senescent component in its development. In commercial settings, an internal disorder with similar symptoms has been observed much sooner after harvest. To ensure successful industry production of this cultivar, it is crucial to understand the management factors that influence the development of this disorder. What are the new findings? Study results suggest that ‘Gem’ pear internal tissues (cortex) are sensitive to either low O 2 , high CO 2 , or a combination thereof, especially shortly after harvest. Physiologically untenable gas levels may be provoked by high internal respiration rates due to incomplete cooling or rapid application of low oxygen-CA shortly after harvest. What are the expected impacts on horticulture? Management strategies successfully mitigating internal breakdown development include air storage, cooling fruit rapidly and completely immediately after harvest, delaying controlled atmosphere until 2–3 weeks after harvest, and maintaining low CO 2 in storage. Results from the present study can also be used to inform future research regarding the minimum internal fruit temperature or maximum whole-fruit respiration rates required to impose CA without provoking internal breakdown.