Lenticel damage on 'B74' mango fruit

Abstract

The mango (Mangifera indica L.) is a fruit crop of considerable economic and social importance.Widely renowned as the king of fruits, mangoes are produced in tropical and sub-tropical regions.In Australia, the cultivar B74 (marketed as Calypso TM ) is a recently developed hybrid cross between Kensington Pride (KP) and Sensation. Damage to lenticels, macroscopic cavities on the surface of fruit that facilitate gas exchange, limits the marketability of B74 fruit. Lenticel damage (LD) exhibits as a dark area surrounding the lenticel cavity, which reduces the visual appeal of the fruit.In the current research, the working hypothesis that high cell turgor within the lenticel cavity predisposes mango fruit to LD that is exacerbated by other stresses was tested.The characteristics and morphology of lenticels during fruit development of B74 and four other mango cultivars were comparatively examined. Lenticels on B74 fruit formed from stomata on young fruit and, more so, from cracking of the cuticle during later stages of fruit growth. B74 fruit had 2-to 7-times higher lenticel density at commercial harvest maturity than KP, Honey Gold and R2E2 fruit. Sensation fruit had a 2-fold higher lenticel density than B74. The high lenticel density on B74 fruit, as inherited from Sensation, may explain its greater susceptibility to developing commercially significant LD. Accumulation of condensed phenolics around damaged B74 lenticels was also observed macroscopically and microscopically. A larger proportion of lenticels on B74 fruit had smaller chambers at commercial harvest as compared to KP, perhaps because more lenticels formed later from cracks. There was no spatial link in terms of close proximity between sub-cuticlar epidermal resin ducts and LD. This lack of association suggests that external stressors are key LD-causing agents.The impact of tree irrigation was investigated towards discerning pre-disposing factors to LD.Withholding irrigation from B74 trees for 3 -8 weeks prior to harvest reduced soil water content and leaf stomatal conductance. However, it had no appreciable effects on either fruit water status or lenticel morphology. The severity of LD on fruit at eating ripe was not reduced by irrigation treatment, although withholding irrigation for 4 weeks prior to harvest increased LD severity on fruit at eating ripe and 7 days after eating ripe. Dipping B74 fruit after harvest into water increased LD severity by ~ 1.7 -2.0-fold after standard commercial pre-harvest irrigation. Exposure of fruit to γ-irradiation also increased LD irrespective of the irrigation treatment. Where fruit do not require irradiation, ceasing irrigation from 3 -8 weeks before harvest might represent a cost saving.iiiThe susceptibility of B74 fruit to developing LD in response to commercial packing house operations, specifically solution dipping and brushing, were investigated. Postharvest operations concomitantly increased LD severity and resulted in pigment accumulation in epidermal cells surrounding the lenticel cavity. LD sever...