Browsing by Author "Holcroft, D. M."

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    Extension of the storage life of plums (Prunus salicina) using controlled atmosphere shipping
    (International Society for Horticultural Science -- ISHS, 2005-06) Mare, L.; Truter, A. B.; Kemp, A. T.; Dodd, M. C.; Holcroft, D. M.; Huysamer, M.
    South Africa is an important supplier of stone fruit to the northern hemisphere in the months of November to March. The voyage by sea to the main markets in the UK and Continental Europe necessitates production of cultivars that are able to maintain an acceptable eating quality for a period of at least four weeks from the time of harvest. Four Japanese plum (Prunus salicina) cultivars were examined with the view to extend their storage life under regular atmosphere (RA) conditions at -0.5°C following either RA or controlled atmosphere (CA) shipping, using either the commercial dual temperature (-0.5°C, 7.5°C, -0.5°C) or a single high temperature (7.5°C) regime. The cultivars included the locally bred ‘Sapphire’, ‘Songold’ and ‘Laetitia’ as well as ‘Angeleno’ which is well known in plum producing countries internationally. Storage life of all four cultivars could be extended for an additional two to three weeks under RA conditions at -0.5°C without adverse effects on quality, provided that CA was applied during the shipping phase, either under the dual or single high temperature regimes. Fruit firmness was best retained under CA (dual temperature) conditions. These fruit also showed the lowest respiration rates, ethylene production rates and internal ethylene content. Skin colour development was better under single high than under dual temperature conditions, and also better under RA than CA shipping.
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    Mealiness of Forelle pears - Quo vadis
    (International Society for Horticultural Science -- ISHS, 2005-04) Crouch, E. M.; Holcroft, D. M.; Huysamer, M.
    ‘Forelle’ (Pyrus communis), a late season blushed pear cultivar grown in South Africa, requires a minimum of 12-weeks cold storage (-0.5 °C) to ripen evenly. Mealiness, a dry texture disorder, may develop at this time. In contrast to other pear cultivars, longer cold storage periods result in less mealiness. This could be related to insufficient total ACC build up and ethylene production, during the first 12 weeks of cold storage, for juicy texture development, during ripening. ‘Forelle’ pears were stored for 3 weeks at -0.5°C, treated with ethylene (100 μL L-1, 24h, 20°C), stored at 20°C for 2 days and thereafter 3 weeks at -0.5°C. Ethylene treatment led to an increase in mealiness after this period. However there were no differences in treated and control fruit following further ripening at 15°C for 7 days. Mealiness could not be linked to insufficient ethylene during shorter storage periods. Harvest maturity, a factor known to influence mealiness, was tested by harvesting fruit 2 weeks prior to commercial harvest, during commercial harvest, and 2 and 4 weeks after commercial harvest. Mealiness occurred at all harvest dates after 6 weeks at -0.5°C and 7 days at 15°C. Storage temperature was also tested as another factor influencing mealiness. Fruit were stored at -0.5°C, 4°C and 7.5°C for 6 weeks and ripened for 7 days at 15°C. Fruit stored at 4°C and 7.5°C ripened with 0 and 8% mealiness, respectively, in contrast to 70% in control fruit. Results could, however, not be confirmed in 2002 and 2003 as all treatments exhibited low mealiness levels (<4%). As high temperatures prior to harvest may influence mealiness, overhead evaporative cooling was applied during 2003 from early fruit development or from 2 weeks prior to harvest. Little to no mealiness developed in all treatments making it difficult to conclude if cooling prior to harvest affects mealiness.
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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.