Researcher: Dr H.J. Maree - 10 Jun 2016

This study aims to identify the mechanism that leads to apparent resistance to grapevine leafroll disease (GLD) that has been observed in individual grapevine plants.

Leafroll virus has a major effect on vines since it interferes with the physiological activity of the plant and shortens the lifespan of vineyards. The subsequent yield and quality losses in grapevines also have an economic impact for the producer.

For many years there have been anecdotal reports of symptomless plants appearing among symptomatic plants in severely grapevine leafroll-diseased vineyards of the Western Cape. Recently, more cases of plants that appear to be resistant against grapevine leafroll disease have been observed in highly infected vineyards, older than 20 years. Despite growing among other severely infected plants for decades, they do not display symptoms of GLD. Subsequent testing also failed to detect any of the common viral pathogens in these plants. These include individual grapevine plants of the cultivars Pinot gris, Pinot noir and Shiraz. The reason for this apparent natural resistance or tolerance is not known, but can possibly be due to viral cross protection by unknown viral variants, by genetic mutation(s) in the plant, or a combination of these. Recent developments in next-generation sequencing now allows for fast processing of a large volume of samples and provides unbiased characterisation of viruses. This advancement in technology is vital to this project to allow researchers to compare and identify viromes in the samples.

Studying the susceptibility or resistance to viruses of plants of the same cultivar, within the same vineyard, provides an ideal opportunity to try to determine the cause of this apparent increased resistance.

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