Attaining the right BERRY
colour is an important quality in coloured table grapes, as consumers associate this with ripe and tasty fruit. Certain production practices, like ensuring appropriate light exposure, plant nutrition and regulating fruit load, can increase berry coloration. However, market requirements and economic conditions mean farmers use production practices that deliver higher yields and larger berry size, which hinders good coloration.Gawie van der Merwe of Capespan informed table-grape farmers who attended a feedback session at the recent International Table Grape Symposium, hosted by the South African Society for Enology and Viticulture (SASEV), about a new growth regulator that increases berry.Called ProTone, this new product has just been released in South Africa and was developed by Valent BioSciences Corporation in the US.
“Unlike growth promoters currently available in South Africa, such as ethephon, this new product doesn’t impede berry development, or cause loss of turgidity and a shortened shelf-life,” says Gawie.And recent information released by the European Food Safety Authority indicated that ethephon use could soon be restricted in various horticultural products sold on European markets. Genetic and climatic factors also affect colouration in table grapes, says Gawie. “The type of cultivar and rootstock, and the virus status of the vines, contribute to how well grapes colour,” he explains.
How does it work?
Abscisic acid (ABA) occurs naturally in plants as a growth regulator. If there are high levels of this present in grape berries, it causes a fast increase of colour pigments in the skin of the grapes.
Under normal conditions, grapes produce enough ABA, but when conditions aren’t ideal, for example when temperatures are too high, more of this is needed. ProTone represents the first registration of the active ingredient ABA and makes it possible to apply this to grapes when needed.“Research for this product started in 2003 and test results have shown that ProTone can enhance colour and provide harvest flexibility in commercial red table-grape varieties such as Crimson Seedless, Flame Seedless and Red Globe under a variety of growing conditions,” says Gawie.He added that the product has been tested in South Africa on these three cultivars, but so far it has only been registered for use on Crimson Seedless. |fw