Abiotic stress improves in vitro biological indexing of Grapevine leafroll-associated virus-3 in red grapevine cultivars

Background and Aims: Virus detection is necessary for in vitro production and propagation of virus-free plants, for in vitro conservation and when material is received from overseas in tissue culture. In vitro biological virus indexing is among the reliable techniques. The aim of the present study was to develop an in vitro graft-free protocol for indexing of Grapevine leafroll-associated virus-3 (GLRaV-3). Methods and Results: In vitro GLRaV-3-infected shoots were cultured on half-strength Murashige and Skoog medium supplemented with either 150 mmol NaCl or 4% polyethylene glycol (PEG) 8000 to induce development of the virus symptoms. After 4 weeks of culture, the proportion of the symptom expression was 86 and 81% for Cabernet Sauvignon, 100 for '6-12-2', 78 and 72% for Red Globe and 70 and 60% for Kyoho in the diseased shoots stressed by 150 mmol NaCl and 4% PEG, respectively. Expression of virus symptoms was more obvious and reliable when in vitro plantlets were stressed by NaCl than by PEG. Conclusions: Salt and drought stress induced by NaCl and PEG 8000 can improve in vitro biological indexing of GLRaV-3 in red grapevine cultivars. Significance of the Study: The techniques developed in the present study would have potential application to GLRaV-3 indexing of red grapevine cultivars.