Polyphasic Analysis of Isolates from Kiwifruit Reveal New Genetic Lineages of Pseudomonas syringae pv. actinidifoliorum Look-Alike

Abstract

Currently, kiwifruit cultivation arouses great economic interest in the agricultural sector in several countries of the European Union due to high consumer demand and good results achieved in terms of production potential and fruit quality. One of the main bacterial species that cause yield losses in kiwifruit plants is Pseudomonas syringae. Diseases such as bacterial canker, caused by pathovar (pv.) actinidiae; floral bud necrosis caused by pv. syringae and leaf spots caused by pv. actinidifoliorum (Pfm) are clear examples. Between 2014 and 2017, in the main kiwifruit producing areas in the north and east of Spain, several surveys were carried out in search of these pathogens. Analyses realized from symptomatic and asymptomatic plants of Actinidiadeliciosa revealed the existence of new bacterial isolates close to Pfm. These new isolates werelow virulence pathogens similar to Pfm but belonging to a new group of P. syringae that affected the leaves of A. chinensis var. deliciosa. This study focused on the characterization and classification of these new isolates by a polyphasic approach in order to provide more information for understanding how the different populations of P.syringae affecting kiwifruit. They had the phenotypic characteristics of Pfm but by molecular approaches, they constituted a supported genetic lineage closely-related to Pfm independent of the five lineages described so far. This work revealed the great diversity found in P. syringae species affecting kiwifruit plants and supports the hypothesis that Pfm is a low virulence pathogen which is long established in Europe.

Occurrence of Pseudomonas syringae pvs. actinidiae, actinidifoliorum and Other P. syringae Strains on Kiwifruit in Northern Spain

“…Three strains isolated from kiwifruit samples collected in the same orchard were grouped with the IVIA 4447 strain that had been deposited as unconfirmed (cf) Pfm. We cannot know if the geographical origin of these strains is the same since Morán et al [41] did not specify this data in their article, in which they only refer to "isolates from Asturias and other areas of Spain". In addition, we have not confirmed them as Pfm since they did not group with the Pfm control strain CFBP 8161.…”

“…Some other locations have been added since then: the area of Salas in 2018 [37], the area of Carreño in 2019 [38] and Piloña and Villaviciosa in 2020 [39]. However, there is no indexed bibliography publishing these results except for the recent reference by Moran et al [41]. These authors describe new genetic lineages of a P. syringae pv.…”

“…In 2020, two outbreaks were detected, one in Asturias and the other in Navarra [35][36][37][38][39]. In addition, Pfm was identified in Galicia [40], and a recent study [41] cites the presence of a bacteria actinidifoliorum look-alike, pending confirmation, in Spain, although without specifying the region.…”