ReTain May Influence Storage Disorders

ReTain is a very useful orchard management tool in terms of delaying fruit maturity and reducing fruit drop. However, there are some reports to be aware of that indicate increased susceptibility to various storage disorders when apples were treated with ReTain.

Bramlage et al. (1980) found that apples treated with ReTain had higher incidences of core browning. Treated 'McIntosh' had an incidence of 56% after storage in air at 0°C for 4 months, compared to 29% in non-treated fruit. Similarly, treated 'Spartan' had an incidence of 43% versus 6% in non-treated fruit. This pheno-menon is thought to be related to delayed fruit maturity due to ReTain, since core browning is worse in immature than in mature apples.

Johnson and Colgan (2002) found that ReTain treated 'Cox's Orange Pippin' developed core flush (30-60%) and internal breakdown (10-55%). Furthermore, both disorders were more severe with ReTain applications closer to harvest (2 or 4 weeks prior), and increasing the concentration of ReTain increased the incidence of internal breakdown.

In short, anything that suppresses ethylene production can cause or aggravate the development of various physiological disorders in apples. Although the exact mechanism behind this effect is not known, it appears that the ability of apples to withstand stresses from high CO₂, low oxygen, and low temperature are reduced where a low rate of ethylene production is maintained during storage. Also in support of this theory, the use of 1-MCP increases fruit susceptibility to CO₂ injury and ethylene removal from storages has been reported to promote core browning, low temperature breakdown, and CO₂ injury in various apple cultivars.