Development of Discolouration in Mango Lenticels W. du Plooy, S. Combrinck and B. Botha C. van der Merwe and T. Regnier Department of Chemistry and Physics Laboratory for Microscopy and Tshwane University of Technology Microanalysis, University of Pretoria Pretoria Pretoria South Africa South Africa Keywords: Mangifera indica, lenticel discolouration, phenolics, morphology, epicuticular wax, electron microscopy Abstract Cultivar dependant discolouration of mango lenticels is a well-known phenomenon. This discolouration is often the reason export fruit are downgraded. Tissue surrounding lenticels progressively becomes affected, but the manifestation and severity of the condition can be unpredictable. Previous research to find and control the trigger of the condition included studies of horticultural aspects, and pre- and postharvest processes. However, with no satisfactory solution apparent, a study of the lenticel morphology and its related chemistry, and the epicuticular wax were undertaken. Three commercially important cultivars from South Africa, ‘Keitt’, ‘Kent’ and ‘Tommy Atkins’, each with a distinctly different level of affliction were used in this study. From the combined results of high performance liquid chromatography and microscopy, several new aspects were elucidated. Cultivars have a structural relationship to discolouration, while chemical profiling and ultrastructural studies of lenticels pointed towards physiological irritation as the stimulus for the development of the condition. INTRODUCTION Lenticels are gaseous exchange facilitators associated with fruit rind, or more correctly, exocarp. The exocarp is primarily composed of natural wax, cutin, epidermal layer, sub-epidermal tissue and may include structures such as stomata and trichomes. Lenticels on mango (Mangifera indica L.) fruit are epidermal structures that also form part of the exocarp due to their superficial nature and integration with sub-epidermal layers. The stomatal origin of mango lenticels gives the best indication of their morphological characterisation, since they are structurally different from the classic lenticels present on other plant species (Tamjinda et al., 1992; Bezuidenhout et al., 2005). Their structural peculiarity, however, has always been overshadowed by economic issues due to their discolouration, the severity of which is related to cultivar (Donkin and Oosthuyse, 1996). Despite susceptible cultivars in South Africa often displaying variable affliction, discolouration of lenticels on mango fruit surfaces is not unique to an area or cultivation practice. Attempts at understanding the aetiology of these lesions include studies of the effect of soil type, meteorological factors, nutritional status, water balance, pest control measures and water baths on the packline (REF). None of these studies can satisfactorily explain the development of the condition, or improve the prediction thereof. This unpredictability causes problems for South African growers when consignments are exported blemish-free, appearing affected by discoloured lenticels at the destination port. Growers are not only concerned about financial loss due to the resultant downgrading of the fruit, but also loss of market confidence. In an effort to understand why some cultivars are more prone to develop discoloured lenticels, the morphology and some chemical aspects of lenticels from ‘Tommy Atkins’, ‘Kent’ and ‘Keitt’ were studied. 665 Proc. VIII th Int. Mango Symposium Ed.: S.A. Oosthuyse Acta Hort. 820, ISHS 2009