The rootstock is the lower part of a grafted plant and provides the root systems. Almost all grapevines that are commercially planted today are grafted on a rootstock. Rootstocks are used to provide an increased resistance against phylloxera (a grape aphid that affects the roots) and are often crosses of American Vitis labrusca, Vitis riparia and Vitis rupestris grape varieties. Plants from these grape species are unlike Vitis vinifera varieties, (partially) resistant to phylloxera. Examples of commonly used rootstocks are: ‘SO4’, ‘3309 Couderc’ and ‘Gravesac’.
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