Studies on the German grapevine yellows (Vergilbungskrankheit)
A grapevine yellows called Vergilbungskrankheit (VK) occurs in several grapevine-growing regions of Germany. It is thought to be similar (or identical) to Bois Noir disease (see RS 95/210), and related to stolbur diseases of solanaceous plants, but distinct from grapevine flavescence dorée phytoplasma (EPPO A2 quarantine pest). In Germany, a PCR procedure has been developed which enables specific amplification of a ribosomal sequence from the phytoplasma-like organism associated with VK and stolbur-related diseases of solanaceous plants. This technique was applied to detect phytoplasmas in grapevine affected by VK and to try to identify alternative host plants and insect vectors of the disease.
Samples from symptomatic plants have been collected from 5 viticultural regions of Germany (Mosel-Saar-Ruwer, Mittelrhein, Rheinhessen, Nahe, Rheinpfalz). In affected vineyards, weeds showing symptoms of a phytoplasma infection and also insects have been collected. Successful amplification was obtained with all grapevine samples prepared from various cultivars collected in different areas. This suggests that the causal agent is a relatively homogeneous organism. This phytoplasma was also detected in naturally infected weeds such as Convolvulus arvensis and Solanum nigrum, and from the planthopper Hyalesthes obsoletus. Feeding of this planthopper on grapevine seedlings induced the development of typical yellow symptoms. This is the first time that a vector of a grapevine yellows, other than flavescence dorée (transmitted by Scaphoidus titanus) has been identified. Although Hyalesthes obsoletus is rather numerous on Convolvulus arvensis, it is rarely found on grapevine; this could explain the slow spread of VK in the field. The authors concluded that the techniques developed in this study are promising tools for further epidemiological studies of VK.
Sources
Maixner, M.; Ahrens, U.; Seemüller, E. (1995) Detection of the German grapevine yellows (Vergilbungskrankheit) MLO in grapevine, alternative hosts and a vector by a specific PCR procedure.
European Journal of Plant Pathology, 101(3), 241-250.