Suppression of Verticillium Wilt of Olive by Pseudomonas fluorescens

Protection of pathogen-free olive planting material from infection by Verticillium dahliae during plant propagation and/or at planting would help in the management of Verticillium wilt of olive. Despite the importance for rhizosphere functioning, rhizobacterial Pseudomonas spp. have been mainly studied in a cultivation-based manner. In this study, 8 isolates of Pseudomonas fluorescens obtained from roots of olive plants were tested for suppression of Verticillium wilt in nursery-produced olive planting stocks under controlled conditions. The antagonistic activity of P. fluorescens isolates from olive against defoliating (D) and nondefoliating (ND) V. dahliae pathotypes. The isolates of P. fluorescens isolates from olive varied in the ability to inhibit hyphal growth of D and ND V. dahliae on PDA. In planta bioassays were conducted under greenhouse conditions, by inoculating bacterial-treated and -nontreated 3- to 4-month-old, own-rooted plants of susceptible olive cv. Zard with the highly and less virulent V. dahliae. Results indicated that root treatment with some of P. fluorescens isolates significantly reduced the final disease incidence and severity, compared with the nontreated controls. Our results indicate that root treatment of olive plants with selected P. fluorescens isolates during nursery propagation can help in the biocontrol of V. dahliae in olive especially for ND pathotypes. No correlation was found between efficacy of tested bacterial isolates for in vitro antagonism of the pathogen and in planta suppression of Verticillium wilt.