LYCHEE (LITCHI-CHINENSIS SONN) PERICARP DESICCATION AND THE IMPORTANCE OF POSTHARVEST MICROCRACKING

Lychee fruit are prone to postharvest desiccation, resulting in browning of the pericarp. Microscopic cracks (20-100 mum wide) in the pericarp surface were observed at harvest and had significantly increasing in density 12 h later. Microcracking extended through the sub-epidermal sclerenchyma layer into the mesocarp. Pericarp desiccation occurred prior to crack development, with cracking the result of dehydration rather than the initial cause. No evidence of cuticle thinning was observed prior to micro-cracking, however, localised cuticle deterioration on the protuberance did occur. We believe that initial pericarp desiccation may be the result of high permeability of the cuticle to water vapour, cuticle damage and the presence of lenticels. Although the cracking did not increase the rate of desiccation, micro-cracks may be important in both exposing the underlying anthocyanin-containing mesocarp tissue to further desiccation, and fungal penetration into the pericarp.