Outside my home is a grapevine. It was there when I moved in and I’m afraid that over the years it has not received huge amounts of attention from me, except to trim it back so I can access my front door. I didn’t know much about grapevines, so living alongside one has been an interesting experience.
Grape an economically important crop in many countries. The vast majority (71 %) are grown for wine-making, with the rest grown for fresh and dried fruit (1). Cultivation of grapes started around 8,000 years ago in the Middle East (1). There is archaeological evidence of wine production in Georgia dating back to a similar time, so wine-making has long accompanied and shaped the domestication of the grape. Indeed, to make wine from grapes, all you really need to do is crush them and leave them for a while in a container with as little air as possible. In these conditions, the sugar in the grapes is fermented into alcohol by yeast that grow naturally on the skins of the fruit. The skill in wine-making is to use the right grapes and know when to stop the fermentation process.
Grapes are now grown in many regions across Europe, the Americas, Asia, Australia and New Zealand. Most of the grapes belong to the species Vitis vinifera, which originates from the Middle East, but some other closely related species from the Americas or Asia are also cultivated, for example Vitis labrusca and Vitis amurensis.
Grapevines die back for the winter and so each spring they produce fresh shoots and leaves. This year, my vine produced its tiny flowers in June. They might not be very impressive-looking, but they don’t need to be, because grape flowers are pollinated by the wind, not insects. The anthers holding the pollen emerge from the flower and the pollen is blown off and to hopefully reach other flowers.
Over the summer months, the fruits develop from fertilized flowers in clusters of 15-300. When they ripen they can be a variety of colours from green right through to dark purple, and even black. My vine produces grapes that become a light-purple/pinky colour when they ripen. White grapes — which are actually green — originate from purple grapes but they have mutations that switch off production of the purple pigments called anthrocyanins.
While the flesh of the fruit is tasty to eat, the seed at the centre of a grape is not. The first seedless grapes were developed from plants that had mutations in seed production, and seedless varieties are now widely grown. Since these varieties do not produce seeds they must be propagated vegetatively, where cuttings from a mature plant are taken and used to make whole new plants.
Every plant has enemies and the grape is no exception. One such enemy is a tiny insect called phylloxera, a relative of the aphid. Phylloxera comes from the US where it lives on native grape species. When Vitis vinifera was introduced to the US in the 19th Century, it was very vulnerable to infection by phylloxera as it had little natural resistance. Unfortunately, phylloxera managed to cross the Atlantic and in the 1860’s it — together with outbreaks of other diseases caused by fungi – devastated the vineyards of Europe. Even today, there is no cure for phylloxera and no chemical control methods available. Instead, cuttings of Vitis vinifera varieties are grafted onto the roots of phylloxera-resistant Vitis riparia (an American species). Phylloxera had a huge impact on the European wine industry for many years, and wine-production in other countries including America, Australia, South Africa and New Zealand rose to fill the gap in supply.
In early Autumn, the grapes ripen and are ready for harvesting. In 2013, my vine produced vast quantities of grapes (see first photo) that a couple of friends harvested and used to make wine. Unfortunately, 2014 has not been a good year, and most of the fruit shrivelled and died over the summer. I’m not sure why this happened, but we had a lot of wet weather and storms in August, which may have encouraged fungi to grow on the fruit.
In 2007, the genome sequence of V. vinifera was published. It was the 4th plant genome to be sequenced and the first of a fruit crop. Armed with the genome sequence, it should be easier to produce new varieties in future, and thus continue the development of grapes that started 8,000 years ago.
All images by the author. Licenced under CC BY-SA 4.0.
1) Wikipedia: Grape (retrieved 28/09/14)
2) Wikipedia: Phylloxera (retrieved 28/09/14)
3) Jaillon et al (2007) The grapevine genome sequence suggests ancestral hexaploidization in major angiosperm phyla. Nature