Endophytic bacterial community is restructured in grapevine yellows-diseased and recovered vitis vinifera L. plants : outcome of plant response to phytoplasma infection and starting point for recovery?

Flavescence doree (FD) and Bois noir (BN), grapevine yellows (GY) diseases associated with phytoplasmas, induce severe crop losses. Until now, none grapevine varieties have been found resistant to phytoplasmas infection (Laimer et al., 2009). FD control is based on chemical treatments against the insect vector, Scaphoideus titanus Ball; on the other hand, this strategy is not efficient for BN containment since biological complexity of this disease. In recent years, there has been an increasing interest about the recovery from GY diseases and in the role of endophytic bacteria as biocontrol agents (Bulgari et al., 2009, 2011). Composition and structure of endophytic bacterial community were examined in healthy, phytoplasma-diseased and recovered grapevine plants. Length heterogeneity-polymerase chain reaction (LH-PCR) of total DNA from grapevine leaves was used to generate amplicon profiles that were analyzed with univariate and multivariate statistical methods. Jaccard analyses highlighted that microbial diversity and structure are different in healthy, diseased and recovered grapevine plants. Multivariate analyses confirmed this trend and showed which LH-PCR peaks determined the variation in microbial composition. Furthermore, LH-PCR electrophoretic peaks, assigned to isolated cultivable single bacterial strains, were used to monitor their distribution in total DNAs from analyzed plants. Bacterial community associated with healthy plants was characterized by a greater richness (higher number of LH-PCR peaks) than that present in diseased and recovered plants. Observed low bacterial richness and different microbial composition in diseased and recovered plants suggest that phytoplasma infection can directly and/or indirectly restructure bacterial community selecting endophytic strains that are able to elicit plant defense response.