EVALUATION OF BIOLOGICAL INDEXING AND DSRNA ANALYSIS IN GRAPEVINE VIRUS ELIMINATION

Fragmented shoot apex culture (FSAC) was used to eliminate some diseas es caused by viruses and virus-like agents from 24 varieties of import ed grapevines. Each cultivar was examined by biological indexing befor e and after FSAC. Graft indexing revealed that leafroll, stem pitting and yellow speckle diseases were common before FSAC. A correlation was observed between the incidence of leafroll disease and the presence o f specific dsRNA species which were removed after FSAC. One of these s pecies, an RNA of about one kilobase pair was associated with low yiel ding Sultana clones. Both biological indexing and dsRNA assay indicate d no recurrence of the leafroll disease in material regenerated by FSA C even after 10 years in the field. It is concluded that dsRNA assay m ay be used as a faster and less expensive method than biological index ing in assessing the success of leafroll elimination by FSAC. The test also provides some information on the genome size of the viruses asso ciated with leafroll disease. Graft indexing indicated that yellow spe ckle disease was resistant to elimination by FSAC, while stem pitting was removed from some of the vines and the grapevine fleck disease was eliminated from most sources.