Aster Yellows disease in vineyards in South Africa

A Technical Guide
for Wine Producers

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Aster Yellows disease in vineyards in South Africa

Roleen Carstens

Roleen Carstens, ARC Infruitec-Nietvoorbij, Stellenbosch

General
Grapevine Yellows disease was for the first time detected in France in 1955 and can be found world wide on several Vitis vinifera varieties. Yellows disease is a collective name for diseases like Flavescence dorée (France), Bois noir (Switzerland), Vergilbungskrankheit (Germany), Australian Grapevine Yellows (Australia) and North American Grapevine Yellows (North America). Yellows symptoms were also detected in Italy, Romania, Hungary, Chile, Israel, Greece, Portugal, Nieu-Zealand, Albania, Croatia, Lebanon, Serbia, Slovenia, Spain, Tunisia, Ukraine and Bulgaria. All Yellows diseases show similar symptoms and the diseases can therefore not be distinguished on symptoms only.
Grapevine Yellows disease is caused by a wide variety of phytoplasmas. The Yellows disease detected in the Western Cape is caused by Aster Yellows phytoplasma. Yellows diseases caused by this specific phytoplasma can also be found in Europe, Israel, North America, Chile and Tunisia. A phytoplasma is a small primitive bacterium without a cell wall that is systemic in the phloem of the plant. All organs can be infected namely the roots, trunks, shoots, buds, flowers and berries but phytoplasmas cannot be found in seed.
Grapevine Yellows disease affects a wide variety of cultivars. Chardonnay is very sensitive but it can also be found on Chenin blanc, Colombar, Pinotage, Cabernet Sauvignon, Cabernet franc, Shiraz, Merlot, Sauvignon blanc, Ruby Cabernet, Pinot noir, Pinot gris and Riesling. Rootstocks do not show symptoms but can act as carriers. Yellows disease was detected in the following table grape cultivars in Greece and Israel: Waltham Cross, Italia, Queen of the Vineyard, Muscat d’Alexandrie and Alphonse Lavallee.
Aster Yellows phytoplasma has a wide range of host plants (about 200) like weeds, cover crops, vegetables and flowers.

Delayed budding on certain parts of the vine (Photo: Jeff Joubert)

Leaves has a wrinkled appearance (Photo: Jeff Joubert)

Yellowing of leaves of white cultivars occurs. Leaves are thicker than normal, crispy and roll downward.

Chardonnay shoots do not lignify and stay green.

Bunch aborts (Photo: Jeff Joubert)

Symptoms
Signs of delayed budding occur on parts of the vine while the rest buds and grows normally. Leaves are crisp with a wrinkled appearance. Shoots stay green and on Chardonnay it has a lead gray colour that can be rubbed off. Shoots have shortened internodes and tips, and young bunches abort.
Later in the season the leaves of white cultivars turn yellow and a reddening of the leaves of red cultivars occurs. Affected leaves are thicker than normal, crisp and they roll downwards. Shoots lignify only partially or not at all. Dieback of shoots takes place from the growth tips as well as partial dieback of fully developed bunches. Water shoots that seem unaffected develop on the trunk and arms of affected vines (especially young vines). Infected vines decline and die eventually.
Transmission
Leaf and plant hoppers (phloem feeders of the Hemiptera) primarily transmit the Aster Yellows in South Africa, but no vector has yet been identified. The phytoplasma is not carried from the infected insect to the next generation. The nymphs need to feed on an infected vine or on an infected host plant in order to transmit the disease.
The phytoplasma can also be transmitted by infected plant material.
Detection
The disease-causing organism can be detected and identified by the very sensitive polimerase chain reaction (PCR) method. The uneven spread of the phytoplasma in the plant and seasonal variation in concentration makes the detection of the disease-causing organism problematic.
Control
When a plant is infected with the phytoplasma there is no control strategy to cure that specific plant. Control must therefore be aimed at the prevention of spreading of the disease:

Infected vines serving as a source of infection should be eradicated.
Weed control should be applied strictly to prevent vectors using the weeds as host plants for over wintering or as host source for the phytoplasma.
When new vineyards are established certified planting material free of phytoplasmas should be used. Heat therapy and tissue culture produce clean planting material as well as hot water treatment of dormant planting material (50°C for 45 minutes) kills the phytoplasmas effectively.
When specific insects are identified as vectors, those insects can be chemically controlled.

References
Directory of Infectious Diseases of Grapevines and Viroses and Virus-like Diseases of the Grapevine: Bibliographic Report 1998 - 2004. 2006. Options Méditerranéennes Série B n.55 p. 133 - 194.
Krake, L.R., N.Steele Scott, M. A. Rezaian & R. H. Taylor. 1999. Graft-transmitted Diseases of Grapevines p. 75 - 102.
Magarey, P.A. 1986. Grapevine Yellows - Aetiology, epidemiology and Diagnosis. South African Journal of Enology and Viticulture, Vol. 7 No.2, p.90 - 100.
Maixner, M., M. Langer., Y. Gerhard. 2006. Grapevine Yellows - Current developments and unsolved questions. Extended abstracts 15th meeting ICVG, Stellenbosch, South Africa, 3 - 7 April 2006, pg. 86 - pg. 87.
M’hirsi S., H. Acheche, S.Fattouch, G.Boccardo, M.Marrackchi and N. Marzouki, 2004. First report of phytoplasmas in the aster yellows group-infecting grapevine in Tunisia. New Disease Reports 9. http://bspp.org.uk/ndr/july2004/2004-10.asp

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