Browsing by Author "Steyn, Natalie"

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    Red colour improvement in apple fruit (Malus domestica Borkh.)
    (Stellenbosch : Stellenbosch University, 2020-12) Steyn, Natalie; Theron, K. I.; Steyn, Willem J.; Crouch, E. M.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Fruit red colour coverage and intensity determine the market value of bi-colour apples. Anthocyanin synthesis and therefore red colour development is highly light- and temperature dependent, the latter being especially challenging in warmer Mediterranean-type climates such as the Western Cape, South Africa. Colour development also occurs simultaneously with fruit ripening, a process that is highly ethylene sensitive. ‘Cripps’ Pink’ and older strains of ‘Fuji’ apples are notorious for poor and erratic colour development thus limiting producer profits. Bi-colour apples are therefore harvested over multiple picking dates mostly based on the extent of fruit red colour development. Preharvest aminoethoxyvinylglycine (AVG) (125 mg٠L-1), 1-aminocyclopropane-1- carboxylic acid (ACC) (200 μL٠L-1) and a combination of the two were evaluated together with postharvest 1-methylcyclopropene (1-MCP), to determine the effect on red colour development, fruit quality and maturity of ‘Cripps’ Pink’ apples. ACC successfully increased percentage blush coverage of fruit and percentage Pink Lady™ pack-out; however, fruit maturity was advanced. AVG on its own resulted in a delay in red colour development, as well as fruit ripening. The combination of ACC and AVG resulted in fruit colour similar to that of untreated control fruit. The effect of ACC (100 μL٠L-1 – 400 μL٠L-1) applied two weeks before harvest on red colour development of ‘Fuji Kiku’ (Brak) and ‘Cripps’ Pink’ apples was evaluated over one and two seasons, respectively. The internal ethylene concentration (IEC) of ‘Cripps’ Pink’ apples was determined. A rapid increase in IEC of fruit after ACC application in both seasons indicated that ACC was taken up by the fruit and converted to ethylene. This resulted in an earlier shift in harvest distribution for both cultivars, indicating stimulation of red colour development by ACC. Loss in fruit firmness, greater starch breakdown and yellower ground colour of fruit treated with higher rates of ACC (300 μL٠L-1 and 400 μL٠L-1) indicate that the advance in red colour development was due to advanced maturity. ACC applied at 200 μL٠L- 1 followed by postharvest 1-MCP treatment showed potential for aiding colour development of bi-colour apples without negatively affecting fruit maturity. Two commercially available reflective mulches, viz. Lumilys® and ColorIt, were installed four to five weeks before harvest and evaluated on ‘Rosy Glow’ and ‘Fuji’ apples to improve red colour development without advancing fruit maturity. Trials were conducted in open orchards as well as under shade netting. Both reflective fabrics performed similarly in reflecting photosynthetically active radiation and increasing red blush colour of both cultivars, especially of the lower canopy fruit, compared to fruit from trees next to grassed alleys. Fruit maturity was largely unaffected by mulch installation, but varying results in parameters such as fruit firmness of ‘Rosy Glow’ apples indicate that this needs to be further investigated. The high initial input cost of reflective mulches might be justified by its improvement of Class one pack-out of fruit as well as its reusability within a season and over various seasons. Overall, the application of reflective mulching seems to be the better way to improve colour in ‘Cripps’ Pink’ and ‘Fuji rather than ACC application.