Fruit pigmentation studies

[摘要] ENGLISH ABSTRACT: For many apple (Malus domestica Borkh.) and pear (Pyrus communis L.)cultivars, attractive colour is essential to their profitability on export markets. Thisstudy focuses on problems related to poor green colour of 'Granny Smith' applesand insufficient red colour of bi-coloured pear cultivars.'Granny Smith' apples often suffer from poor green colour. Green colour of fruitfrom various orchards was already found to differ midway through fruitdevelopment, with these differences being carried through to harvest. In a trialwhere nitrogen (N) fertilisers were applied using different forms at different times,there was no improvement in green colour. In another trial, artificial shading wasapplied to fruit only during their early development. Fruit that were shaded duringthis time were less green at harvest than unshaded fruit. Additional Napplications may only improve colour where a deficiency exists. However, greencolour may be improved by increasing light distribution early during fruitdevelopment.Bi-coloured pears attain their maximum red colour midway through theirdevelopment, and this desired red colour is mostly lost prior to harvest. Redcolour can also increase transiently with the passing of cold fronts. Anthocyanins,responsible for this red colour, may have a photoprotective function which wouldexplain this pigmentation pattern, as photosystems are particularly sensitive tolight damage at low temperatures. As 'Rosemarie' fruit bent over from a verticalto hanging position during development, peel photoinhibition was reduced asanthocyanins were synthesised. 'Forelle' peel was found to be very sensitive tohigh light levels at low temperatures. Substantial anthocyanin development tookplace in 'Cripps' Pink' apples when weather conditions were cold, but clearfollowing a cold front. A photoprotective role seems to explain daily changes inanthocyanins in response to temperature, but not the seasonal progression ofcolour development. For many apple (Malus domestica Borkh.) and pear (Pyrus communis L.)cultivars, attractive colour is essential to their profitability on export markets. Thisstudy focuses on problems related to poor green colour of 'Granny Smith' applesand insufficient red colour of bi-coloured pear cultivars.'Granny Smith' apples often suffer from poor green colour. Green colour of fruitfrom various orchards was already found to differ midway through fruitdevelopment, with these differences being carried through to harvest. In a trialwhere nitrogen (N) fertilisers were applied using different forms at different times,there was no improvement in green colour. In another trial, artificial shading wasapplied to fruit only during their early development. Fruit that were shaded duringthis time were less green at harvest than unshaded fruit. Additional Napplications may only improve colour where a deficiency exists. However, greencolour may be improved by increasing light distribution early during fruitdevelopment.Bi-coloured pears attain their maximum red colour midway through theirdevelopment, and this desired red colour is mostly lost prior to harvest. Redcolour can also increase transiently with the passing of cold fronts. Anthocyanins,responsible for this red colour, may have a photoprotective function which wouldexplain this pigmentation pattern, as photosystems are particularly sensitive tolight damage at low temperatures. As 'Rosemarie' fruit bent over from a verticalto hanging position during development, peel photoinhibition was reduced asanthocyanins were synthesised. 'Forelle' peel was found to be very sensitive tohigh light levels at low temperatures. Substantial anthocyanin development tookplace in 'Cripps' Pink' apples when weather conditions were cold, but clearfollowing a cold front. A photoprotective role seems to explain daily changes inanthocyanins in response to temperature, but not the seasonal progression ofcolour development. Dwarfing rootstocks are known to improve red colour of bi-coloured pears due toimproved light distribution. 'Forelle' fruit from six rootstocks of varying vigour wereharvested from exposed positions only, so as to establish the effect of rootstockon red colour development independent of the effect of rootstock on canopy lightdistribution. Fruit from trees on quince (Cydonia oblonga Mill.) rootstocks werefound to have redder fruit than those from vigorous BP pear rootstocks. This maybe due to higher chlorophyll and carotenoid concentrations present in the peel offruit from BP rootstocks, whose leaf and peel N were also high. The use ofquince rootstocks is recommended where red colour development of bi-colouredpears is a problem.An early season bi-coloured cultivar with good red colour is required. Breedingtrials to find such a cultivar are resource intensive. To streamline the process, amethod to preselect immature seedlings for their future fruit colour is required.Fruit colour from bearing seedlings was compared with colour of their immatureleaves. Trees with red leaves were likely to produce fruit that were too red for thebreeders' requirements. Trees with green or blushed leaves were capable ofproducing blushed fruit. It would be feasible to cull red-leaved seedlings withminimal risk of losing potential bi-coloured cultivars.

[发布机构] Stellenbosch University