Project title
Investigation of the virus status of grapevines cv. Shiraz clone 99 affected with Shiraz decline disorder using molecular methods.

Project leader
Goszczynski, D E

Institution
ARC Plant Protection Research Institute

Team members
Jooste, A E C
Kasdorf, G G F

Project description
Vitivirus and Foveavirus specific RT-PCR amplification of dsRNA, extracted from a nucleus plant of Shiraz clone 99B infected with Shiraz decline, followed by cloning, SSCP analysis of clones and sequencing, showed that this plant is infected with uniform populations of viruses related to RSPaV-SY and GVB. The result was intriguing as RSPaV-SY type strain was reported by USA researchers as closely associated with Syrah (syn. Shiraz) decline and GVB is associated with corky bark disease. Symptoms of corky bark resemble, in many aspects, those of Shiraz decline. Virus status analysis of field-collected plants of various local Shiraz clones with different Shiraz decline status, using the same technique as described above, did not however reveal an association of these viruses with the disease. Application of GVB specific RT-PCR also did not reveal the association of GVB with the disease. Further study of GVB demonstrated that not all variants of the virus are detected by standard RT-PCR. New primers, which were designed using available sequences of ORF1 of various GVB variants, did not improve detection of the virus. To overcome the extensive molecular variability of GVB, further search for identical sequences in the 3rd terminal part of various variants was initiated. The work is in progress. This study also revealed that the RSPav-SY strain, despite that it was recently reported as closely associated with Shiraz decline, was present in various
local clones of Shiraz affected and not affected by the disease. Continuation of study of the association of viruses, especially GVB, with Shiraz decline is of primary importance for the South African grapevine industry. The virus is transmitted by the mealybug Planococcus ficus, which is common in local vineyards. Results may have far reaching consequences for South African viticulture.

Presentation(s)
1. Goszczynski, D E. 2007. Study of virus status of Shiraz clone 99B infected with Shiraz decline reveals intriguing facts but do not lead to finding of clear-cut association of viruses with the disease. 2 May. Grapevine Virus workshop VII, Infruitec, Stellenbosch, South Africa.

Final report
http://www.sawislibrary.co.za/dbtextimages/FinalReport131.pdf

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