Quantifying the role of vapour pressure deficit in the development of lenticel breakdown in Braeburn apples

The aim of this project is to establish whether pre-and post-harvest factors (influencing the vapour pressure deficit (VPD)) of the fruit will influence the fruit quality and in particular lenticel disorders. The aim is also to document the different lenticel disorders photographically with light microscopy.

In trial 1, the anatomical and morphological development of lenticels on ‘Braeburn’ apples was studied from 40 to 166 DAFB. In trial 2, delayed cooling and the use of wet blankets in relation to fruit quality and lenticel disorders was investigated. Trial 3 investigated pre-cooling treatments such as passive and forced air cooling at different temperatures. Re-cooling at different fan speeds and the use of liners was studied in trial 4. 

In trial 1, lenticel developmental stage was not influenced by canopy side. Transitioning of stomata into lenticel was only observed from 82 DAFB onwards, a bit later compared to other apple cultivars.

Trial 2 showed delayed cooling without a wet blanket increased cumulative VPD significantly. Delayed cooling advanced maturity.

Trial 3 found that LB incidence, fruit weight loss and firmness were not significantly affected by the pre-cooling treatments.

In trial 4, punched and micro-perforated liners showed a slower re-cooling rate, extended re-cooling time, lower cumulative VPD and reduced fruit weight loss.

Fruit quality was generally maintained in all post harvest treatments with the exception of delayed cooled apples being slightly more mature than immediately cooled apples. The use of wet blankets reduced VPD. However, wet blankets, immediate or delayed cooling did not have a significant effect on LB incidence. FAC or passive pre-cooling did not show a consistent effect on LB incidence. Re-cooling treatments at different speeds show no effect on LB incidence. The use of liners reduced VPD and weight loss. However, effects on LB incidence were not found.

Post-harvest treatments did not consistently affect LB incidences. Factors that were investigated such as weight loss, VPD and cooling temperatures and rates whether it was pre-cooling or re-cooling did not seem to have a direct effect on LB. Therefore, results indicate that LB is initiated during pre-harvest and not primarily by storage regimes.