The effect of different fertilizer application levels on anthocyanoplast development in berry skin of Pione grapevines (<i>V. vinifera</i> x <i>V. labrusca</i>)
Effects of different levels of a complete liquid fertilizer on grape berry coloration and anthocyanoplast (ACP) development in the skin were investigated. Four-year-old vines of cv. Pione (a tetraploid hybrid of Vitis vinifera L. and V. labrusca L.) were planted in root zone-restricted beds and were treated with normal (N), high (H; Nx1.5), and excessively high (EH; Nx2) levels of a commercial liquid fertilizer. Fertilizer levels were decreased to one third after veraison to accelerate berry ripening. Skin anthocyanin contents in N- and H-treated berries increased at a constant rate after veraison, while the contents in EH berries were significantly lower. ACPs were first observed in epidermal cells at veraison in N and H berries and 2 weeks later in EH berries. In each treatment formation of ACPs in hypodermal cells occurred one week later than in epidermal cells. In each treatment the number of epidermal cells containing ACPs increased during ripening of the berries but the number of hypodermal cells with ACPs increased only in N vines. The average numbers of ACPs per epidermal and hypodermal cell were largest in N vines, followed by H and EH vines (two weeks after veraison). The number of ACPs decreased thereafter because most ACPs coalesced. The average ACP diameter at full ripeness was 16.7 μm in N vines, whereas in H and EH vines it was 9.5 μm and 9.7 μm, respectively. From these results, it can be deduced that in Pione grape berries high fertilizer levels inhibit ACP formation both in epidermal and hypodermal cells at veraison and/or induce their coalescence thereafter, resulting in poor coloration.
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