Micrografting Grapevine for Virus Indexing

Grapevine (Vitis vinifera L.) is a widespread and highly valuable horticultural crop. Around 2.25 million ha are grown worldwide, mainly in the southern temperate zone and in the subtropics. Italy (8.6 million Mt from 0.84 million ha), France (6.8 million Mt from 0.85 million ha), the United States (7.1 million Mt from 0.38 million ha), Spain (6.1 million Mt from 1.17 million ha) and China (6.6 million Mt from 0.45 million ha) are the main producers, accounting for half the total world production of 66 million Mt (FAOSTAT data, 2007). More recently, substantial increases in the plantings in the southern hemisphere (Australia, South Africa, Argentina, Brazil and Chile) have been driven by the increasing wine exports from these countries.

Expansion of grape cultivation in many countries has been based on imported grapevine stocks of established cultivars and this trend is continuing. Importation of grape varieties to establish new vineyards increases the risk of previously unknown viruses being introduced. Importantly, planting materials obtained locally to establish new vineyards must also be free from viruses. It is estimated that global losses due to viral infection of grapevines are over 1 billion US dollars due to effects such as yield reduction, maturity delay, reduced sugar content in the fruit and decreased plant vigour. However, the means to reduce losses caused by viral infection once a vineyard is established are extremely limited. Therefore, it is important to have robust, sensitive, rapid and reliable techniques for assessing grape clones for any viral infections they may carry.

The successful application of micrografting in grapevine for the detection of GLRaVIII, which has substantially different symptoms to corky-bark, indicates that there is scope to apply the micrografting procedure for routine virus indexing following its successful application to other viruses. It may, however, be used already to detect leafroll and corky-bark viruses, based on the success of the established methods