Early detection of Grapevine leafroll-associated virus 3 in a table and raisin grape germplasm collection in Central California

Caused by grapevine leafroll-associated virus 3 (GLRaV-3), grapevine leafroll disease (GLRD) is one of the most devastating viral diseases in most grape-growing regions worldwide. Unfor­tunately, due to a lack of understanding of the GLRaV-grape­vine interaction, there are currently no applicable measures to cure GLRaV-3 infection. Most effective GLRD control strategies include planting certified virus-free grapevines and removing virus-infected vines through rogueing. Therefore, early detec­tion of GLRaV-3 is critical for the timely removal of infected plants in the vineyard. Here, we evaluated the efficiency and accuracy of GLRaV-3 early detection by RT-PCR using a table and raisin grape germplasm collection in California’s Central Valley. The results were verified by late detection using enzyme-linked immunosorbent assay (ELISA). We found that the efficacy of RT-PCR-based GLRaV-3 early detection highly depends on the genotypes. Some GLRaV-3-infected germ-plasm could be detected by RT-PCR at an early stage, while other lines either generated inconsistent results between in­dividual plants or exhibited only negative outcomes; however, they were almost all later confirmed to be GLRaV-3 positive by ELISA. The inconsistency is probably due to slower virus propa­gation and disease development in these lines. We also found that despite the lower GLRaV-3 early detection rate, all positive RT-PCR results are accurate and can be used to guide timely vine removal to prevent GLRaV-3 spread. Early detection of GLRaV-3 across various varieties and breeding lines provides valuable germplasm-dependent guidance for table and raisin grape growers and researchers in Central California, enabling them to initiate disease management as early as in April. With necessary modifications, the guidance can also be applied to GLRaV-3 management in vineyards outside of our region.