The biological bases of recovery of two grapevine cultivars, Nebbiolo and Barbera, showing different susceptibility and recovery ability to "flavescence dorée" (FD) phytoplasma infection were investigated. The expression over one vegetative season, in FD-recovered and healthy grapevines, of 18 genes involved in defence, hydrogen peroxide and hormone production was verified at two time points. Difference (Δ) between the relative expressions of August and July were calculated for each target gene of both cultivars. The significance of differences among groups assessed by univariate and multivariate statistical methods, and sPLS-DA analyses of the Δ gene expression values, showed that control and recovered grapevines of both cultivars were clearly separated. The Barbera-specific deregulation of defence genes supports a stronger response of this variety, within a general frame of interactions among H2O2, jasmonate and ethylene metabolisms, common to both varieties. This may strengthen the hypothesis that FD-recovered Barbera grapevines modulate transcription of their genes to cope with potential damages associated to the alteration of their oxidative status. Nebbiolo variety would fit into this picture, although with a less intense response, in line with its lower degree of susceptibility and recovery incidence to FD, compared to Barbera. The results evidenced a scenario where plant response to phytoplasma infection is highly affected by climatic and edaphic conditions. Nevertheless, even after several years from the original FD infection, it was still possible to distinguish, at molecular level, control and recovered grapevines of both cultivars by analyzing their overall-season response, rather than that of a single time point.
Keywords: Phytoplasma; Quantitative RT-PCR; Recovery; Vitis vinifera.
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