FACTORS AFFECTING THE INCIDENCE OF 'RUSSET BROWNING' DISORDER IN 'COX'S ORANGE PIPPIN' APPLES

The ethylene antagonist, 1-methylcyclopropene, is used commercially as SmartFresh^SM to retain firmness during shipping and storage of ‘Cox’s Orange Pippin’ apples. However, the application of SmartFresh^SM can result in an unsightly darkening of the russeted area in the stem cavity. The symptoms have been termed ‘russet browning’ disorder. Several studies have been undertaken over the last five seasons. In initial studies, fruit held in bins or cartons were treated with a full or reduced rate of SmartFresh^SM to determine the effects of maturity at harvest, time after harvest, SmartFresh^SM dose and pack type on the incidence of ‘russet browning’ after storage. Results indicated that the incidence of ‘russet browning’ could be reduced by reducing the rate of 1-methylcyclopropene without a significant loss in firmness retention, and that delaying treatment from three days after harvest to seven days after harvest increased the incidence. Pack type, i.e., treating fruit in bins or cartons, had no consistent effect on ‘russet browning’. In subsequent studies, the incidence of ‘russet browning’ was decreased if fruit were treated with a reduced rate of 1-methylcyclopropene after cooling rather than before cooling, and the disorder could be avoided if fruit were treated after cooling and kept cold throughout storage. However, if fruit were given a warming treatment to simulate packing after treatment and short-term storage, the incidence of ‘russet browning’ increased the earlier and longer the fruit were warmed after SmartFresh^SM treatment. It is concluded that ‘russet browning’ disorder can be avoided if fruit are treated with a reduced rate of SmartFresh^SM after packing and cooling and then keeping the fruit cold throughout subsequent storage. Avoiding excessive warming in the first two weeks after treatment is likely to be useful in reducing the incidence of ‘russet browning’, but the disorder could be totally avoided if treated fruit were held at storage temperatures for 6-8 weeks before packing or marketing.