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Jan-Louis Bezuidenhout and Hannes Robbertse

Discoloration of the lenticels of some mango cultivars is a serious problem, affecting the economic value of the fruit. Mango fruit lenticels develop from ruptured stomata on fruit from 20 mm in `TA' and `Keitt' and 30 to 40 mm in `Kent'. Lenticels enlarge as the fruit grow due to stretching of the fruit surface. Adult lenticels of `TA' and `Keitt' are larger in size than those of `Kent'. `Kent' lenticels are also better insulated than `TA' and `Keitt', having a thick cuticle in the lenticel cavity and, in some instances, a phellogen is also present where `TA' and `Keitt' lack both of the above mentioned. Resin present in the skin of the fruit play an important role in the discoloration of `TA' and `Keitt' lenticels. Resin of both `TA' and `Keitt' fruit contain a considerable amount of an aggressive compound termed terpenes. These terpenes are volatile and able to move out of the resin ducts via the sublenticellular cells to the outside of the fruit. The integrity of tonoplasts situated in sublenticellular cells are lost due to the presence of terpenes, causing vacuolar bound phenols to come into contact with polyphenol oxidase, present in the cell walls. The product of the resultant reaction is a quinone, accumulating as a brownish deposit in the cell walls, the black markings visible from the outside. This is the spontaneous discoloration process. Lenticel discoloration may also occur due to maltreatment, i.e., rough handling, to high temperatures, extended period on brushes on the packline, breaking of the cold chain, and spilling of resin onto the surface of the fruit.

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Hannes Robbertse, Jaco Fivaz, and Chris Menzel

The architecture of the lychee tree and the structure of the inflorescence are described according to the terminology of Hallè et al. and Weberling. The lychee tree has rhythmic modular growth and the inflorescence is a heterocladic pleiothyrsoid. Additional paracladia may develop from a second serial bud below the first-order paracladia. Male and female flowers are borne at variable positions on the dichasia. The relation between the position and gender of the flowers on the partial inflorescences (dichasia) varied with cultivar and time.