Browsing by Author "Wand, S. J. E."

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    Harvest and post-harvest apple fruit quality following applications of kaolin particle film in South African orchards
    (2006) Wand, S. J. E.; Theron, K. I.; Ackerman, J.; Marais, S. J. S.
    Sunburn on apples in the Western Cape region of South Africa can result in yield losses of up to 50%. Application of kaolin-based particle film (Surround® WP) increases leaf and fruit surface reflectivity, thus potentially reducing heat load and sunburn. Trials were performed during 2002/2003 and 2003/2004 to assess the effectiveness of kaolin particle film in controlling sunburn on 'Granny Smith', 'Braeburn', 'Fuji', 'Royal Gala' and 'Cripps' Pink' apples. Fruit quality and ripening were monitored following 1-4 months in regular atmosphere cold storage at -0.5°C. Sunburn on exposed fruit was significantly reduced in 'Granny Smith' and 'Fuji'. Kaolin treatment improved fruit colour of 'Granny Smith' and 'Royal Gala', and delayed starch conversion in 'Granny Smith' at harvest and during the early storage period but not thereafter. Incidence of watercore at harvest was significantly reduced by kaolin treatment, but this disorder disappeared during cold storage in both treatments. There were no effects on skin anthocyanin or phenolic concentrations in any cultivar compared to unsprayed fruit. © 2005 Elsevier B.V. All rights reserved.
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    Red colour development and loss in pears
    (International Society for Horticultural Science -- ISHS, 2005-04) Steyn, Willem J.; Wand, S. J. E.; Holcroft, D. M.; Jacobs, G.
    The endogenous and environmental regulation of red colour development in blushed and fully red pears is reviewed. Colour development in pears has an underlying developmental component. Generally, highest anthocyanin concentrations are attained in immature pears and colour tends to fade towards harvest. This is contrary to most other crop species where maximum pigmentation and colour are attained in ripe fruit and may relate to the photoprotective ability of anthocyanins. Because of this pigmentation pattern, net anthocyanin degradation at high temperatures results in pre-harvest red colour loss in susceptible pear cultivars. Susceptibility depends on the capacity to accumulate anthocyanin and on whether low temperatures are required for anthocyanin synthesis. Unlike apples, where red colour development in all cultivars seems to require or benefit from low temperatures, not all pear cultivars seem to respond to low temperatures. Light appears to have two opposing effects in pears, being required for anthocyanin synthesis, but also apparently increasing red colour loss through increased degradation of anthocyanin.
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    Use of evaporative cooling to improve ' Rosemarie' and ' Forelle' pear fruit blush colour and quality
    (International Society for Horticultural Science -- ISHS, 2005-04) Wand, S. J. E.; Steyn, Willem J.; Holcroft, D. M.; Mdluli, M. J.; Van Den Dool, K.; Jacobs, G.
    In Pyrus communis ‘Rosemarie’, a potentially lucrative blushed pear cultivar, poor fruit colour has been ascribed to pre-harvest red colour loss during periods of high temperature. High temperatures combined with high irradiances also lead to sunburn on pome fruit. The use of pulsed overhead evaporative cooling (EC) to improve red colour and reduce sunburn in two blushed pear cultivars was evaluated over four seasons (2000/01 to 2003/04) in Stellenbosch, South Africa. ‘Rosemarie’ fruit blush was usually but not always improved under EC, with a late application (starting two weeks before harvest) yielding the best improvement. Peel anthocyanin concentrations were increased under EC. Incidence of sunburn was reduced during some years, but increased in EC-treated fruit during 2003/04 due to system failure on a hot day. EC initiated early in fruit development initially led to larger fruit with a lower TSS concentration and firmness, but this effect was gradually eliminated following reductions in EC water use. EC had no effect on ‘Forelle’ pear fruit colour or mass, but reduced firmness and TSS when started early in the season. Sunburn was only recorded in EC-treated fruit during 2002/03 due to system failure on a warm day. Though EC could be used to improve ‘Rosemarie’ fruit colour in warm production areas, its effect was relatively small compared to colour change in response to fluctuating temperature. The increased risk of sunburn during system ‘downtime’ highlights the requirement for a highly reliable system.