2.2 - 2.3 Recognizing grapevine leafroll disease symptoms in South Africa: White-berried cultivars and Rootstocks

Prof Gerhard Pietersen, University of Pretoria - 27 Apr 2016

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2.2 White-berried cultivars

In white-berried grapes the symptoms of grapevine leafroll disease are very mild and can often not be seen. A few cultivars (Chardonnay, Cape Riesling, Semillon) will show mild yellowing or chlorotic mottling of interveinal areas of leaves, which in some (e.g. Chardonnay) may progress to a downwards rolling of the leaf margins. In general, if symptoms are observed on these cultivars the grapevines are already severely infected. In some cultivars (Sauvignon blanc, Riesling) the disease never shows obvious symptoms and can be considered latent throughout the course of the disease.

In white berried cultivars that show some symptoms, it is not known how long the latent period of the disease is, but this is likely to differ depending on the age of the grapevine when infected, whether the grapevine was infected via mealybugs or infected scion material or infected rootstock material, and various environmental conditions. However it is likely to be multiple seasons.

2.3 Leafroll in rootstocks

Rootstocks (e.g. Vitis riparia, V. rupestris, V. berlandieri, V. champini, and crosses thereof e.g. Richter 110, Richter 99, LN-33, 101-14) do not show any symptoms of leafroll infection but can harbor the virus (GLRaV-3). The virus is generally is in low concentration and/or erratically distributed in rootstock material. The diseased nature of rootstocks is obvious once healthy new scion material is top-grafted onto rootstocks from an old, previously leafroll infected vineyard, and is a practice that should be avoided.

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