Protocol for the assessments of Grapevine virus infections

The assessment of the sanitary status of clonal selections and propagating materials of grapevines requires the use of assays providing clear-cut and highly reliable virus identification. Results depend on the type of test, reagent, diagnostic kit, and on the timing of sampling. Whereas analysis of mature canes usually gives reliable ELISA and PCR responses for all viruses, assays from leaf samples collected in summer are less dependable. Concerning Grapevine leafroll-associated virus 1, 2, and 3, positive detection from leaves is only partially consistent with the presence of symptoms. Reliable ELISA or PCR detection was obtained from the beginning of the after berry set stage onwards from basal leaves, and from the beginning of veraison stage onwards from median leaves. ELISA tests for Grapevine virus A and Grapevine fleck virus from mature leaves gave 30% less positive responses as compared with mature canes. PCR assays yielded more reliable results. Diagnosis of Rupestris stem pitting-associated virus by PCR was possible from both mature canes and leaves.