First report of phytoplasmas in the aster yellows group infecting grapevine in Tunisia

In northern Tunisia, grapevines (Vitis vinifera) were found exhibiting symptoms of grapevine yellows that included plant weakness, incomplete lignification, flexible shoots and drooping. Affected leaves were thicker than normal, brittle, rolled downward and showed veinal yellowing and necrosis (Fig 1A). In addition, grape bunches became dry and shrivelled before fruit could fully develop and ripen (Fig 1B). Given the symptoms that were observed, a phytoplasma infection was suspected.

DNA was extracted using an enrichment procedure (Gundersen et al., 1996) from 27 symptomatic grapevines and was analysed by PCR, using the universal 16S rRNA phytoplasma primer pair R16R2/F2 (Lee et al., 1993). The resulting products were reamplified using the group-specific rRNA primer pair R16(I)R1/F1 (Lee et al., 1994). Seven grapevine samples each yielded a nested rDNA product of 1,100 base pairs. No products were amplified using DNA extracted from healthy grapevines. When the nested-PCR products were digested with either HhaI, MseI or RsaI endonucleases, the restriction profiles obtained were uniform indicating that infected grapevines all contained very similar or co-identical phytoplasmas (Fig. 2).

Likewise, profiles were also indistinguishable from those obtained after HhaI, MseI or RsaI digestion of R16(1)R1/F1 products obtained from control DNA extracts, made from European aster yellows phytoplasma infected samples and included for comparative purposes. Collectively, rDNA restriction profiles delineated phytoplasmas infecting Tunisian grapevine as aster yellows (16SrI-B) subgroup strains (Lee et al, 1998). This is the first report of phytoplasmas in the aster yellows group infecting grapevine in Tunisia.