Browsing by Author "Van der Westhuizen, Marno Wiehan"
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- ItemThe use of plant growth regulators to improve apple pedicel length and reduce fruit cracking(Stellenbosch : Stellenbosch University, 2020-04) Van der Westhuizen, Marno Wiehan; Theron, K. I.; Steyn, Wiehann J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.ENGLISH ABSTRACT: Maintaining apple fruit quality is complex and factors such as short fruit pedicels and fruit cracking reduce quality. Fruit pedicels of certain cultivars in the Elgin-Grabouw-Vyeboom-Villiersdorp (EGVV) region are problematic as they tend to be short, stubby and rigid and cause losses pre- and post-harvest. Fruit pedicel dimensions also vary within trees, complicating the control of the problem. Gibberellin A4 and A7 (GA4+7) on its own and in combination with 6-benzyladenine (6-BA) were evaluated to improve the pedicel lengths of ‘Nicoter’, ‘Fuji’ and ‘Cripps’ Pink’, without having significant side-effects on fruit set, yield, fruit quality and return bloom. We also evaluated the effect of three bearing shoot types (terminal on spur, short shoot and long shoot) on the inflorescence composition as well as the effect of the three shoot types and two flower positions in the inflorescence (king and lateral) on pedicel dimensions and flower, and subsequent fruit quality. Gibberellins A4+7 successfully increased the pedicel length of ‘Nicoter’, ‘Fuji’ and ‘Cripps’ Pink’ apples when applied multiple times between tight cluster and full bloom. Although higher rates of GA4+7 (100 and 200 mg·L-1) significantly increased the pedicel length, the lower rates (10 to 50 mg·L-1) gave fewer negative side-effects on fruit set, yield and return bloom. The recommended treatments to increase pedicel length are 50 mg·L-1 GA4+7, applied twice, 10 mg·L-1 GA4+7, applied four times, and 20 mg·L-1 GA4+7, applied twice for ‘Nicoter’, ‘Fuji’ and ‘Cripps’ Pink’, respectively. Regarding the variable pedicel dimensions, neither the flower position, nor the type of bearing shoot had strong effects on the pedicel size and further research is needed to identify the origin of the intra-plant variation in pedicel lengths. Fruit cracking on ‘Fuji’ (pedicel-end) and ‘Rosy Glow’ (calyx-end) has become a problem in the Ceres region during the past few seasons. GA4+7 on ‘Fuji’ and GA4+7 + 6-BA on ‘Fuji’ and ‘Rosy Glow’ were thus applied at an early and later period during the cell division phase of fruit growth to reduce cracking without causing side-effects on fruit set, yield, fruit quality and return bloom. Unfortunately, due to specific weather conditions and adjustment of management practices, no cracking was observed in the two seasons, except for low levels of pedicel-end cracking on ‘Fuji’ after controlled atmosphere storage in the second season. The return bloom of ‘Fuji’ was, however, reduced by all the GA4+7 and GA4+7 + 6-BA rates (10, 20 and 40 mg·L-1) during the first season and decreased linearly with increasing rate of GA4+7, applied seven, 14 and 21 days after full bloom (d.a.f.b). It also decreased linearly with increasing rate of GA4+7 + 6-BA, applied seven, 21 and 35 d.a.f.b. during both seasons. Higher rates of GA4+7 and GA4+7 + 6-BA should thus be used with caution when considered for cracking control.