From the root to the stem: interaction between the biocontrol root endophyte Pseudomonas fluorescens PICF7 and the pathogen Pseudomonas savastanoi NCPPB 3335 in olive knots.

M Mercedes Maldonado-González,Cayo Ramos,Jesús Mercado-Blanco,Pilar Prieto

doi:10.1111/1751-7915.12036

M Mercedes Maldonado-González, Cayo Ramos + Show 2 more

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https://doi.org/10.1111/1751-7915.12036

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Abstract

Olive knot disease, caused by Pseudomonas savastanoi pv. savastanoi, is one of the most important biotic constraints for olive cultivation. Pseudomonas fluorescens PICF7, a natural colonizer of olive roots and effective biological control agent (BCA) against Verticillium wilt of olive, was examined as potential BCA against olive knot disease. Bioassays using in vitro-propagated olive plants were carried out to assess whether strain PICF7 controlled knot development either when co-inoculated with the pathogen in stems or when the BCA (in roots) and the pathogen (in stems) were spatially separated. Results showed that PICF7 was able to establish and persist in stem tissues upon artificial inoculation. While PICF7 was not able to suppress disease development, its presence transiently decreased pathogen population size, produced less necrotic tumours, and sharply altered the localization of the pathogen in the hyperplasic tissue, which may pose epidemiological consequences. Confocal laser scanning microscopy combined with fluorescent tagging of bacteria revealed that when PICF7 was absent the pathogen tended to be localized at the knot surface. However, presence of the BCA seemed to confine P. savastanoi at inner regions of the tumours. This approach has also enabled to prove that the pathogen can moved systemically beyond the hypertrophied tissue.

Highlights

Pseudomonas savastanoi pv. savastanoi (Psv) (Gardan et al, 1992; Sisto et al, 1999) is the causal agent of olive (Olea europaea L.) knot disease (Kennelly et al, 2007; Ramos et al, 2012) and an unorthodox member of the Pseudomonas syringae complex, encompassing at least 60 pathovars and several other Pseudomonas species (Gardan et al, 1999; Bull et al, 2010; Young, 2010)
In vitro antagonism assays using different culturing media [Potato Dextrosa Agar (PDA), King’s B Agar (KBA), and Luria– Bertani Agar (LBA)] showed that strain PICF7 strongly inhibited the growth of Psv NCPPB 3335 in PDA plates (Fig. S1)
Results showed that when P. fluorescens PICF7 was inoculated into the stems along with the pathogen, population size of NCPPB 3335 sharply decreased and was significantly (P < 0.05) lower during the first 2 weeks after bacterization, compare with that scored in plants only inoculated with Psv

Summary

Introduction

Pseudomonas savastanoi pv. savastanoi (Psv) (Gardan et al, 1992; Sisto et al, 1999) is the causal agent of olive (Olea europaea L.) knot disease (Kennelly et al, 2007; Ramos et al, 2012) and an unorthodox member of the Pseudomonas syringae complex, encompassing at least 60 pathovars and several other Pseudomonas species (Gardan et al, 1999; Bull et al, 2010; Young, 2010). Savastanoi (Psv) (Gardan et al, 1992; Sisto et al, 1999) is the causal agent of olive (Olea europaea L.) knot disease (Kennelly et al, 2007; Ramos et al, 2012) and an unorthodox member of the Pseudomonas syringae complex, encompassing at least 60 pathovars and several other Pseudomonas species (Gardan et al, 1999; Bull et al, 2010; Young, 2010). Infection of olive by Psv results in overgrowth formation (tumours, galls or knots) on the stems and branches of the host plant and, occasionally, on leaves and fruits. Psv NCPPB 3335, a highly virulent strain both in adult trees (Pérez-Martínez et al, 2007) and in micropropagated olive plants (Rodríguez-Moreno et al, 2008; 2009), is being used as a model organism for the study of the molecular basis of the disease onset and development (tumour formation) in woody hosts. The draft genome sequence of NCPPB 3335 (Rodríguez-Palenzuela et al, 2010) and the closed

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