Lenticel discolouration in mango (Mangifera indica L.) fruit - a cytological study of mesophyll cells from affected tissue.
Plooy G. W. du, Merwe C. F. van der, Korsten L.
Author Affiliation: Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria, 0002, South Africa.
Journal of Horticultural Science and Biotechnology 81 : 869-873
Abstract : Mango fruit is characterised by the presence of lenticels, with some cultivars prone to a condition known as 'lenticel damage'. The condition manifests itself as a localized red-to-dark discolouration around the lenticels. The presence of these unacceptable spots on mature green fruit has economic implications. The cytological nature of lenticel discolouration was investigated as part of a study of affected mango fruit. Lenticels were dissected from physiologically mature fruit in predetermined groups of varying discolouration. Transmission electron microscopy and light microscopy of mesophyll cells from affected tissue indicated conservation of cellular structures and endomembranes in all variants of discolouration. It was therefore shown that the accumulation of cell wall-bound phenolics does not result from structural damage such as vacuolar collapse or membrane disintegration. Results further suggest the apoplastic transport of the signal for phenolics deposition. Accumulation of phenolic compounds in a distinct zone of affected tissue around the lenticel creates a barrier between the atmosphere and the rest of the mesophyll. Although lenticel discolouration is an inherent self-defence mechanism supported by continued metabolic activity, it is a superficial, cosmetic defect.