Peel water vapour permeance of Japanese plums as indicator of susceptibility to postharvest shriveling

Moisture loss and postharvest shrivelling of some Japanese plum cultivars result in significant financial losses in the South African stone fruit industry. Even though fruit are stored at optimal temperatures and packaging solutions are implemented to reduce shrivel, the incidence of shrivel is still unacceptably high in susceptible cultivars. Fruit peel water vapour permeance (PH2O) can be calculated to determine the proneness of a cultivar to moisture loss. Knowledge of the status of the PH2O prior to harvest and the variation between cultivars, orchards and seasons could indicate whether newly developed cultivars are prone to postharvest shrivel. This could assist in determining the optimum handling protocols for susceptible cultivars to reduce potential moisture loss. The PH2O of various cultivars were determined during 2015/16 and 2016/17. In addition, to establish whether a relationship exists between postharvest fruit moisture loss and shrivel, weight loss and shrivel incidence was recorded on individual fruit of the cultivars Sapphire, Laetitia and African Delight™ during 2016/17. PH2O varied between seasons, cultivars and orchards. In 'African Rose', 'Ruby Sun' 'Ruby Star' and 'Sapphire', high PH2O corresponded with known shrivel susceptibility. 'Songold', 'Fortune' and 'Angeleno' are not prone to shrivel and these cultivars had a low PH2O. However, 'Laetitia' and 'African Delight™' had low PH2O, even though both cultivars are prone to shrivel. Pre-harvest moisture loss and PH2O could therefore not be used to predict shrivel susceptibility successfully for evaluated cultivars.