Cytokinin involvement in post-harvest litchi pericarp browning

Litchi (Litchi chinensis Sonn.), a popular member of the Sapindaceae family, is a sub-tropical fruit tree bearing high market-value fruit, due to the attractive red peel, and the unique flavor of the fruit aril. Unfortunately, one of the main challenges met by the growing litchi industry is the rapid deterioration of litchi fruit pericarp color, following detachment of the fruit from the tree, due to pericarp browning. The process of litchi fruit pericarp browning is tightly associated with modifications in fruit pericarp anatomy. In litchi fruit, pericarp micro-cracking was associated with enhanced anthocyanin oxidation and post-harvest fruit deterioration due to pericarp browning. Examination of the genetic variation behind litchi fruit post-harvest pericarp browning demonstrate that the cultivar ‘Hong Long’ that displays significantly thicker pericarp also displays reduced susceptibility to post-harvest water loss and pericarp browning, as compared to ‘Mauritius’. Interestingly, exogenous application of the plant hormone cytokinin during the phase of pericarp cell-division increased pericarp thickness, reduced postharvest water loss and postponed post-harvest pericarp browning of ‘Mauritius’ which is highly sensitive to pericarp browning. Indeed, early cytokinin treatment, during pericarp cell division phase, yield fruits with thicker pericarp, and thicker layer of highly lignified-brachischlareid cells just beneath the fruit epidermis. The data presented suggest that cytokinin treatment can be used to modify fruit pericarp anatomy and reduce litchi fruit susceptibility to post-harvest pericarp browning and water loss.