The Syrah Vine Health Symposium provided an opportunity for virologists and other researchers from France, South Africa and the US to come together at UC Davis and present what they knew about the causes of abnormal Syrah vine growth to members of the California winegrape industry. It also provided scientists with an opportunity to observe symptoms in local Syrah vineyards, and to discuss differences in symptomology and focus on avenues of investigation that are most likely to provide an answer to the cause of Syrah Decline. Along with the symposium, a French journal article was translated to English; and recordings of seminar presentations as well as the symposium proceedings were posted on the internet.
Syrah (synonym Shiraz) is grown throughout California vineyard regions, with a total of 18,776 acres statewide (2006). Beginning in the late 1990?s, growers statewide began reporting abnormal vine growth in some plantings. In the North Coast, the appearance of abnormal graft unions and red leaves are observed on several clones of syrah on a range of rootstocks. In the Central Coast, beginning about 2001, an increasing number of plantings displayed reddish-brown leaves in mid-summer that appeared to be a blend of leafroll virus, potassium deficiency, salt toxicity and/or severe water stress ? a group of symptoms locally referred to as ?Syrah Disorder?.
Symptomology varies across regions; however a group of common symptoms include a swollen trunk just above or occasionally at the graft union; deep vertical cracks in the bark; distorted trunks; and closely spaced nodes along the trunk. When the bark is removed on such vines, deep necrotic pits are found in the wood just above the union as well as necrotic areas that sometimes involve half or more of the diameter of the trunk. Leaves on such vines turn fully red in late summer, and depending on severity of the wood necrosis, shoot growth is stunted. Symptoms are observed in vines as young as 3 years, and death results in severe cases.
Researchers in France, South Africa and Australia have focused their attention to vine health issues in Syrah. In France, symptoms were first reported in 1993 and currently all Syrah vineyards contain some degree of affected vines. Symptoms are referred to collectively as ?Syrah Decline? and are similar to those previously described as being common to some coastal vineyards in California. A formal program to research the cause of Syrah Decline was established in 2001 in ENTAV (L’Etablissement National Technique pour l’Amélioration de la Viticulture). In South Africa, Shiraz has been shown to be infected with a virus associated with symptoms collectively referred to as ?Shiraz Disease?. Similar symptoms have been reported by researchers in Australia. In earlier work, UC had identified a new strain of Rupestris Stem Pitting virus (RSPa-SY) in a symptomatic Syrah vine. In 2007, symptomatic and asymptomatic Syrah vines located in coastal and foothill regions in California were tested for the new strain, but no correlation was found between the virus and symptoms.