Abstract
In recent years, Chilean kiwifruit production has been affected by the phytopathogen Pseudomonas syringae pv. actinidiae (Psa), which has caused losses to the industry. In this study, we report the genotypic and phenotypic characterization of 18 Psa isolates obtained from Chilean kiwifruits orchards between 2012 and 2016 from different geographic origins. Genetic analysis by multilocus sequence analysis (MLSA) using four housekeeping genes (gyrB, rpoD, gltA, and gapA) and the identification of type III effector genes suggest that the Chilean Psa isolates belong to the Psa Biovar 3 cluster. All of the isolates were highly homogenous in regard to their phenotypic characteristics. None of the isolates were able to form biofilms over solid plastic surfaces. However, all of the isolates formed cellular aggregates in the air–liquid interface. All of the isolates, except for Psa 889, demonstrated swimming motility, while only isolate Psa 510 demonstrated swarming motility. The biochemical profiles of the isolates revealed differences in 22% of the tests in at least one Psa isolate when analyzed with the BIOLOG system. Interestingly, all of the isolates were able to produce indole using a tryptophan-dependent pathway. PCR analysis revealed the presence of the genes aldA/aldB and iaaL/matE, which are associated with the production of indole-3-acetic acid (IAA) and indole-3-acetyl-3-L-lysine (IAA-Lys), respectively, in P. syringae. In addition, IAA was detected in the cell free supernatant of a representative Chilean Psa strain. This work represents the most extensive analysis in terms of the time and geographic origin of Chilean Psa isolates. To our knowledge, this is the first report of Psa being able to produce IAA. Further studies are needed to determine the potential role of IAA in the virulence of Psa during kiwifruit infections and whether this feature is observed in other Psa biovars.
Highlights
Pseudomonas syringae pv. actinidiae (Psa) is the causal agent of bacterial canker in Actinidia deliciosa and Actinidia chinensis that has caused severe losses in all of the major areas of kiwifruit cultivation, including Italy, China, New Zealand, and Chile (Scortichini et al, 2012; Ferrante and Scortichini, 2015)
The 18 Chilean Psa isolates used in this study were collected from kiwi plants with canker disease symptoms by the SAG
An multilocus sequence analysis (MLSA) using the housekeeping genes gyrB (DNA gyrase B), rpoD, gltA, and gapA showed that the genes sequenced have 100% identity with the corresponding genes in different Psa strains belonging to biovar 3, including Chilean strains obtained in 2010
Summary
Pseudomonas syringae pv. actinidiae (Psa) is the causal agent of bacterial canker in Actinidia deliciosa and Actinidia chinensis that has caused severe losses in all of the major areas of kiwifruit cultivation, including Italy, China, New Zealand, and Chile (Scortichini et al, 2012; Ferrante and Scortichini, 2015). Actinidiae (Psa) is the causal agent of bacterial canker in Actinidia deliciosa and Actinidia chinensis that has caused severe losses in all of the major areas of kiwifruit cultivation, including Italy, China, New Zealand, and Chile (Scortichini et al, 2012; Ferrante and Scortichini, 2015). This bacterium infects host plants by entering natural openings and wounds, moving inside the plant, and promoting the appearance of necrotic leaf spots, red exudate production, and canker and necrosis in the trunk. A potential new biovar was described in Japan, which produces both phaseolotoxin and coronatine (Fujikawa and Sawada, 2016)
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