Uneven distribution of stolbur phytoplasma in Italian grapevines as revealed by nested-PCR

The distribution and persistence of stolbur phytoplasmas were investigated in grapevines affected by "bois noir" (BN). The phytoplasma was detected using nested-PCR from different plant tissues. In summer it was more frequently detected in symptomatic leaf samples (96.8%), whereas only a low proportion of positive samples was obtained from symptomless leaf samples (12.5%). The analysis of phloem samples from symptomatic and asymptomatic shoots, only revealed a positive reaction (11.1%) with the former. In the same BN-affected grapevines checked during winter, only a low proportion of dormant cane (19%), cordon (8.3%) and root (9%) samples were PCR-positive. Moreover, the pathogen was never detected in trunk or in leaf samples collected from recovered grapevines. The present data indicate an uneven distribution of stolbur in infected grapevines and that the phytoplasma seldom persistently infect plants from year to year.