Identification of factors involved in the expression of internal browning in Fuji apples and the development of a strategy to reduce risk of incidence

In 2015, unacceptable levels of internal browning (IB) (up to 80%) reported for shipments of Fuji apples to the Far East lead to many claims.

The objective of this trial was to investigate factors that resulted in IB expression in Fuji apples; to develop a predictive test for the risk of IB expression and to develop an industry protocol that will reduce the risk of IB expression

Eight Fuji orchards, with a history of IB were selected in the Koue Bokkeveld and EGVV areas. Fruit were harvested at optimum and 10 to 14 days after optimum, taken to CA storage facilities immediately after harvest and again 3 weeks after harvest and evaluated after ± 6 months CA cold storage and 4 weeks RA.

As a means of predicting IB, fruit were subjected to 50% CO₂ for 3 days after harvest at ambient temperature and evaluated daily for IB to compare to IB expression after 6 months cold storage

2016: two orchards exhibited high levels of IB after shelf life. One of the orchards exhibited high IB incidence on fruit from both harvests. Later harvested fruit had higher incidence of this disorder. Two out of the three instances where IB was detected, RA had the highest incidence. Core flush was detected in fruit from the first harvest of one population. RA stored fruit had the highest incidence of this disorder.

2017: low to no IB was detected after cold storage and shelf life. High incidence of core flush was detected in later harvested fruit. RA stored fruit had the highest incidence of this disorder.

2018: IB incidence was higher in later harvested fruit. RA stored fruit generally developed the highest incidence of IB. Core flush incidence was higher in earlier harvested fruit compared to later harvested fruit. RA stored fruit had higher core flush incidence compared to fruit from the other regimes

Some conclusions can be made from the data over the 2016 to 2018 seasons:

• IB and core flush are seasonal
• IB and core flush risk is orchard Some orchards are more prone to develop IB than others.
• IB was generally more prone to develop in later harvested fruit.
• RA stored fruit generally exhibited the highest incidence of internal browning and core flush
• Three to four weeks delay before CA initiation (3wkCA) resulted in fruit with slightly higher IB compared to fruit moved to CA within the first 7 days after harvest (CA). There is however, not a clear distinction between the two storage regimes regarding IB incidence.
• The CO₂ predictive test did produce fruit with IB, but correlated poorly with IB incidence after storage.