SAMPLING STRATEGIES FOR THE DETECTION OF GRAPEVINE FANLEAF VIRUS AND THE GRAPEVINE STRAIN OF TOMATO RINGSPOT VIRUS

This study was conducted to determine the influence of season, host genotype virus isolate and sample tissue on ELISA detection of the two nepoviruses. Enzyme-linked immunosorbent assay (ELISA) readily detects grapevine fanleaf virus (GFLV) and the causal agent of grapevine yellow vein, tomato ringspot virus (TomRSV) in infected grapevines. Three serologically identical isolates of GFLV (fanleaf deformation, vein-banding and yellow mosaic) were examined in one cultivar of Vitis rupestris SCHEELE and in three cultivars of V.. vinifera L. TomRSV was examined in V. vinifera cv. Carignane. The tissues tested included: shoot tips, mature leaves and cambial scrapings. The following tissues taken from GFLV-infected dormant canes were also tested: sawdust, cambial scrapings, dormant buds, and induced shoots, roots and callus. There were no differences in GFLV ELISA results when different cultivars and virus isolates were compared. However, seasonal differences in ELISA detection of GFLV were observed. Shoot tip values went from a high of > 4.00 OD450 nm in May to a low of 0.05 OD450 nm in September. 'Mature leaves also gave the highest values in May and rapidly decreased to relatively low and constant levels throughout the rest of the season. ELISA values from cambial scrapings were moderately high and relatively constant throughout the season. When GFLV-infected dormant canes were tested, induced actively growing tissues gave the highest ELISA values. TomRSV ELISA values were relatively constant over the season and shoot tips, mature leaves and cambial scrapings produced similar ELISA values.