Non-chemical storage technologies for apple and pear superficial scald prevention

Previously, the South African apple and pear industry relied on diphenylamine (DPA) for controlling superficial scald disorder; however, increasing consumer concerns and reductions in maximum residue levels (MRLs) highlighted the urgent need for alternative control strategies. These alternative technologies need to be tested for the South African pome fruit industry to determine whether superficial scald incidence is prevented during long term storage, and if it contributes to better fruit quality and shelf-life. The overall aim of this project is to examine the potential of non-chemical storage technologies to control superficial scald in ‘Granny Smith’ and ‘Packham’s Triumph’

Granny Smith was harvested at two maturities and four treatments (RLOS+ULO-CA, RLOS+CA, DCA and RA) were applied. Three treatments (RLOS+ULO-CA, RLOS+CA and RA) were applied to optimum harvested Packham’s Triumph. Fruit quality evaluations were done after each shelf-life period.

In the 2015 season, RLOS+ULO-CA was effective in preventing superficial scald on pre- optimum and optimum Granny Smith up to 10 months with 7 day shelf-life. DCA and RLOS+CA effectively controlled scald on pre-optimum fruit up to 8 months while on the optimum fruit DCA was effective until 10 months and RLOS+CA until 8 months. All low oxygen treatments resulted in firmer fruit and better skin colour retention, with generally no differences between them. In 2016 pre-optimum fruit stored under RLOS+CA already had superficial scald after 4 months with 7 day shelf-life, RLOS+ULO-CA had superficial scald after 6 months and DCA after 8 months. On the optimum apples, all the low oxygen treatments had superficial scald after 6 months with 7 day shelf-life.

In 2015 and 2016 season RLOS+ULO-CA and RLOS+CA was effective in preventing superficial scald on optimum Packham’s Triumph up to 10 months with 14 day shelf-life. These treatments resulted in firmer fruit with better skin colour retention than the RA treatment. No off-tastes were detected.

For two seasons RLOS was effective in preventing superficial scald development on Packham’s Triumph for long term storage. It is just important to monitor the alcohol concentration after each stress period. RLOS was only effective to prevent superficial scald on Granny Smith for long term storage in the first season. The 2016 season had a very high potential for superficial scald development and the technology was not effective enough to prevent the physiological disorder.