Screening the Olive Tree Phyllosphere: Search and Find Potential Antagonists Against Pseudomonas savastanoi pv. savastanoi

Abstract

Olive knot (OK) is a widespread bacterial disease, caused by Pseudomonas savastanoi pv. savastanoi ( Pss ), which currently has not effective control methods. The use of naturally occurring microbial antagonists, such as bacteria, as biocontrol agents could be a strategy to manage this disease. The objective of this work was to select bacteria from olive tree phyllosphere able to antagonize Pss using in vitro and in planta experiments. The elucidation of their modes of action and the potential relationship between antagonism and bacteria origin has been investigated, as well. To this end, 60 bacterial isolates obtained from the surface and inner tissues of different organs (leaves, twigs, and knots), from two olive cultivars of varying susceptibilities to OK, were screened for their in vitro antagonistic effect against Pss . A total of 27 bacterial strains were able to significantly inhibit Pss growth, being this effect linked to bacteria origin. Strains from OK-susceptible cultivar and colonizing the surface of plant tissues showed the strongest antagonistic potential. The antagonistic activity was potentially due to the production of volatile compounds, siderophores and lytic enzymes. Bacillus amyloliquefaciens P41 was the most effective antagonistic strain and their capacity to control OK disease was subsequently assayed using in planta experiments. This strain significantly reduces OK disease severity (43.7%), knots weight (55.4%) and population size of Pss (26.8%), while increasing the shoot dry weight (55.0%) and root water content (39.6%) of Pss -infected olive plantlets. Bacterial isolates characterized in this study, in particular B. amyloliquefaciens P41, may be considered as promising biocontrol candidates for controlling OK disease.

Identification and Characterisation of Pseudomonas savastanoi pv. savastanoi as the Causal Agent of Olive Knot Disease in Croatian, Slovenian and Portuguese Olive (Olea europaea L.) Orchards

“…Despite the challenges, this observation raises the question of whether antagonistic organisms in the surveyed Portuguese region may have infected those trees subsequent to Pss infection and consequently suppressed further proliferation of Pss . The presence of Pss has been detected in Portuguese orchards that also harbour various bacterial species identified as antagonists of Pss [ 34 ], which may contribute to the suppression of Pss growth in the cases we have described.…”

“…The only non-pathogenic bacteria identified by MALDI–TOF were C. flaccumfaciens and B. megaterium . The effects of the co-infection of these bacterial species with Pss needs to be investigated to determine whether they exert a suppressive effect on Pss growth in infected olive trees [ 33 , 34 ]. Whilst typical symptoms of olive knot disease were observed in all surveyed Portuguese orchards, Pss as the causal pathogen was confirmed only in two samples.…”

Confronting stresses affecting olive cultivation from the holobiont perspective

“…For instance, bacteria isolated from symptomatic olive plants were identified as promising candidates for biocontrol against P. savastanoi pv. savastanoi (Krid et al, 2012;Maldonado-Gonzaĺez et al, 2013;Mina et al, 2017;Filiz Doksöz and Bozkurt, 2022), and diseases caused by pathogenic fungi. In the latter cases, inhibitory effects on conidial germination (Salman, 2017) and growth (Al-khatib et al, 2010) of V. oleaginea have been reported.…”

Isolation and Characterization of Endophytes Against Bacterial Blight of Pomegranate

“…savastanoi), and a total of 27 bacterial strains were able to significantly inhibit Pseudomonas savastanoipv. savastanoi growth (Mina et al, 2020) suggesting that isolates from both cultivars may use different modes of action to protect host plant from Pseudomonas savastanoi pv. savastanoi infection and also noted that endophytes exhibit a lesser inhibition potential against Pseudomonas savastanoi pv.…”