In vitro biological indexing of grapevine leafroll‐associated virus 3 in red‐ and white‐berried grapevines (Vitis vinifera)

Background and Aims Virus detection is essential in programs in which virus‐tested plants are required. The aim of this study was to establish in vitro biological methods for indexing grapevine leafroll‐associated virus‐3 (GLRaV‐3) in red‐ and white‐berried grapevines. Methods and Results Healthy, red‐berried grapevine Cabernet Sauvignon [CaSa (H)] was used as a rootstock in micrografting experiments with virus‐infected Cabernet Sauvignon [CaSa (VI)] and Chardonnay [Ch (VI)] scions. Vascular bundles connecting the rootstock and scions developed, and 100% of the micrografts survived 3 and 4 weeks after micrografting, respectively. Symptoms of GLRaV‐3 were expressed in 80 and 20% of CaSa (H) rootstocks micrografted with CaSa (VI) and with Ch (VI) scions, respectively, 12 weeks after micrografting. The rootstock CaSa (H) that had been micrografted with CaSa (VI) and Ch (VI) scions for 5 weeks was subsequently cultured on half‐strength Murashige and Skoog medium supplemented with 75 mmol/L NaCl to induce salt stress. The GLRaV‐3 symptoms were expressed in 88% of micrografts CaSa (VI)/CaSa (H) and 85% of micrografts Ch (VI)/CaSa (H) after 5 weeks of salt stress. Reddish‐purple leaf coloration and downward rolling were observed in CaSa (H) rootstocks that were micrografted with CaSa (VI) scions, while leaf downward rolling and yellowing were seen in CaSa (H) rootstocks that were micrografted with Ch (VI) scions. Conclusions Salt stress improved in vitro biological indexing of GLRaV‐3 in grapevines. Significance of the Study Establishment of in vitro micrografting and salt stress provided alternative methods for indexing of GLRaV‐3 in red‐ and white‐berried grapevines.