Dear Wine Master,
What is the genus for grapes?
I am assuming that your enquiry about grape genus is for those varieties which bear fruit best suited for the production of wine.
Although not exclusively so, the vines from which all the best known wine grapes are cultivated are of the Vitis vinifera species. This is of European origin and until the late 19th century wine grapes of this genus were grown on their own roots . . . and then the dreaded Phylloxera parasite struck!!
You might like to look at History of Wine to get an idea of the devastation to European vineyards caused by this small aphid. It was eventually realised that the answer to the problem lay in finding root stock which was resistant to phylloxera. The best suited of these was (and still is) the native American species, Vitis rupestris. Today all V. vinifera vines are grafted onto American root stock before planting out in the vineyard.
Viticulture throughout the old and new world has benefited from this development, and all the traditional wine producing grapes continue to flourish. You will find descriptions for some of the best known grapes at Grape Varieties.
I hope this helps.