Lenticel development and discolouration in the fruit of some mango (mangifera indica L.) cultivars

Abstract

Lenticels are macroscopic openings occurring on the surface of roots, shoots and some fruits like apples, pears, avocados and mangos and are responsible for gaseous exchange and transpiration. The discolouration of the lenticels of some mango cultivars is a serious problem, affecting the economic value of the fruit, especially in ‘TA’ and ‘Keitt’ while problems with lenticel discolouration are seldom found in ‘Kent’. Mango fruit lenticels develop from ruptured stomata on fruit from about 20 mm in ‘TA’ and ‘Keitt’ and 30 to 40 mm in ‘Kent’. Lenticels enlarge as the fruit grows due to stretching of the fruit surface, reaching their maximum size on adult fruit. Fully developed 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, while both of above mentioned characteristics are absent in ‘TA’ and ‘Keitt’. Resin present in the skin of the fruit plays an important role in the discolouration of ‘TA’ and ‘Keitt’ lenticels. The resin of both ‘TA’ and ‘Keitt’ fruit contain a considerable amount of an aggressive compound termed terpenes. These terpenes are volatile and are able to move out of the resin ducts via the sublenticellular cells to the outside of the fruit through the lenticels. The integrity of tonoplasts of the sublenticellular cells are lost due to the action of the 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, visible from the outside as black markings around the lenticels. Lenticel discolouration may, however also occur due to maltreatment or rough handling of fruit, high temperatures in the warm water bath, extended brushing on packline or breaking of the cold chain and spilling of resin onto the surface of the fruit. Copyright 2005, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Bezuidenhout, JLJ 2005, Lenticel development and discolouration in the fruit of some mango (mangifera indica L.) cultivars, MSc(Agric) dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-03072006-120414 / >