Elmi Lötze, Stephan H. Daiber, Stephanie J. E. Midgley

Boron in combination with calcium reduces sunburn in apple fruit

Sunburn damage on apple fruit has been reported widely [1]. Sunburn incidence is expected to increase in future, specifically in the Western Cape in South Africa, with very clear climate change predictions [2]. Sunburn thus has significant financial implications on profitability for the South African export dominated apple industry, as sunburnt fruit is not accepted in the main export markets. In the United Kingdom, no visible sunburn on apples is allowed, whereas only fruit with class 1 sunburn (Sunburn classification guide [3]) is accepted in Europe. To reduce sunburn, which can be 40% for some cultivars, an affordable and sustainable alternative is needed. Researchers [4] reported that Manni-Plex® calcium (Ca) and boron (B), applied in combination as pre-harvest foliar applications, reduced sunburn significantly for ‘Golden Delicious’ (GD) apples. This research was continued to investigate the efficacy of the Ca/B combination as alternative formulations on GD. The biggest reduction in sunburn incidence was found in sunburn class 1. Results indicated that more formulations will be suitable to reduce sunburn on GD significantly compared to the control than the initial sorbitol formulation. The Spraybor (5 g)/Calsol combination applied as six weekly foliar applications from 28 days after full bloom (DAFB) was the most efficient combination to reduce sunburn on GD in 2015/16.

Keywords:

Golden Delicious, peel mineral analyses, Sunburn browning,

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