Decreased Detectability of Grapevine Leafroll-associated virus 3 in Sakasly Grapevines Cultivated Under the Sahara Conditions

The detectability of grapevine-leafroll-associated virus 3 (GLRaV-3) was investigated by enzyme-linked immunosorbent assay (ELISA) and reverse-transcriptase polymerase chain reaction (RT–PCR) in the domestic grapevine cultivar Sakasly, grown over two successive years in the Sahara, at Rjim-Maˆ atoug in Tunisia. Self-rooted cuttings, infected with GLRaV-3 were cultivated and the presence of the virus was checked over 2 years and compared with controls. During the first year, 80% of the originally infected vines were negative for GLRaV-3 using ELISA. After the second year, 93% and 95% of these plants were negative for GLRaV-3 using ELISA and RT–PCR, respectively. Furthermore, rooted cuttings derived from GLRaV-3- negative plants and grown under controlled conditions in a greenhouse (at 16–20 C) were ELISA-negative in most cases (84%). In addition, biological indexing on Vitis vinifera cv. Gamay Rouge de la Loire showed no leafroll symptoms on this indicator in 92% of the grafted vines. These results suggest a naturally occurring heat therapy in the Tunisian Sahara, which could be of practical importance for the production of GLRaV-3-free grapevine cuttings, especially as scale insect and mealybug vectors have not been observed in this area.