Colour differentiation of high-lycopene tomato fruit through the addition of the colourless-epidermis (y) mutation

High-lycopene tomatoes (Solanum lycopersicum) are characterised by an intense red flesh-colour, due to an elevated concentration of the carotenoid, lycopene. However, this characteristic is only visible once fruit are cut open, making it impossible to differentiate intact high-lycopene fruit from standard tomato fruit, a clear market disadvantage. The reason that fruit colour of both high-lycopene and standard fruit looks almost identical from the outside is because tomato fruit normally contain the yellow flavonoid 'naringenin chalcone' in a thin layer of epidermal cells. It is this combination of naringenin chalcone and the underlying lycopene in the flesh that gives tomatoes their characteristic orange-red colour. By incorporation of the recessive colourless epidermis mutant allele 'y' (which prevents naringenin chalcone accumulation) into high-lycopene fruit, we have been able to create high-lycopene tomatoes (hp1.ogc.y) exhibiting a deep-pink colour visible from the outside. Hue angle of the skin of the high-lycopene 'y' mutant and a regular highlycopene tomato (hp1.ogc.Y) was 30 and 38°, respectively, while flesh values were similar at 31 and 32°, respectively. Removal of naringenin chalcone from the epidermis appeared to improve the visibility of underlying lycopene, such that fruit outer colour became a subsequent indicator of underlying flesh colour. The removal of epidermal pigmentation means that high-lycopene fruit can now be differentiated from standard tomato fruit in the market place without the need to cut fruit open.

Infection, colonisation and sporulation by Pseudocercospora macadamiae on macadamia fruit

The structures and manner with which Pseudocercospora macadamiae penetrates, colonises and proliferates from the pericarp of macadamia fruit was studied using scanning electron microscopy and fluorescence light microscopy. Germ tubes arising from conidia penetrated open stomata within 20 h of inoculation, without observation of specialised infection structures such as appressoria. Colonisation of the pericarp was intercellular, without observation of specialised intracellular infection structures such as haustoria, and was complete from the epidermis to the mesocarp. The fungus proliferated at the epidermis by the formation of conidiophores and conidia on substomatal and protuberant subepidermal stromata. These structures were not observed on the mesocarp surface. The onset of visual husk spot symptoms coincided with an increase in pathogen biomass on the pericarp surface. The progression of symptoms from tan-coloured spots to larger red-brown lesions coincided with the production of conidiophores from substomatal and protuberant subepidermal stromata. The darker the colour of the husk spot lesion, the more frequently protuberant subepidermal stromata were observed. These findings are discussed in the context of observation of other cercosporoid fungi.

Reducing the incidence of under-skin browning in 'Honey Gold' mango (Mangifera indica L.) fruit

'Honey Gold' mango is a relatively new cultivar in Australia, with an appealing skin colour and a sweet fibre-free flesh. However, fruit can develop 'under-skin browning' (USB), which appears several days after packing as a distinct 'bruise'-like discolouration under the epidermis and can affect large areas of the fruit surface. We investigated the anatomy of USB and the impact of post-harvest fruit handling conditions on the disorder. Starch accumulated around the resin canals and discoloured cells in the affected area, with no visible change to the cuticle or epidermis. Delays of 1 d at ambient temperature (27 degrees - 35 degrees C) before packing, and 2 d at 18 degrees - 20 degrees C (after packing), before placing fruit at 12 degrees - 14 degrees C and road transportation, reduced the incidence of USB by 83% compared to placing fruit at 12 degrees - 14 degrees C within 13 h of picking. The incidence of USB was 88 100% higher in fruit that were cooled to 12 degrees - 14 degrees C within 13 h of picking, then commercially road-freighted for 4 d at 12 degrees - 14 degrees C, than in fruit held under similar temperature conditions, but not road-freighted. Wrapping each fruit in bubble-wrap to minimise direct contact with other fruit, with the plastic insert, or with the cardboard tray, reduced the incidence of USB by 84% after road-freight compared to not using bubble-wrap. These results suggest that USB is a unique disorder of mango skin associated with a rapid post-harvest reduction in temperature, from high ambient temperatures to 12 degrees - 14 degrees C, and with physical damage during road-freight.