Fig. 4

Potato-onion VOCs and dipropyl disulfide stimulate the colonization of tomato roots by specific bacterial isolates. A Neighbor-joining tree based on bacterial 16S rRNA gene sequences of isolates taxonomically affiliated with Pseudomonas and Bacillus spp. Bootstrap was based on 1000 permutations and the obtained values are shown at the branching points. The sequence similarity of each Pseudomonas and Bacillus spp. isolates with OTU5587 and OTU114, respectively, is provided between parentheses. B Schematic representation of the experimental set-up and the twin-chamber system used to test the colonization of bacterial isolates on tomato roots. Tomato plants were grown in sterile soil inoculated with a mixture (1:1) of the bacterial isolates RV33 and RV57. These treatments were exposed to potato-onion VOCs (+ VOC) or not (− VOC) or exposed to dipropyl disulfide (+ DDS) or not (− DDS). C Effects of potato-onion VOCs and dipropyl disulfide on tomato plant growth and on the abundance of RV33 and RV57 in the tomato plant rhizosphere. Data are shown as mean ± SEM (n = 6). Different letters indicate significant differences between treatments (Tukey’s HSD test, p < 0.05)