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First, fourth, fifth, ninth, and tenth authors: Department of Agricultural Sciences, Plant Pathology, Alma Mater Studiorum-University of Bologna, Bologna 40127, Italy; second and eleventh authors: Universidad de Chile, Facultad de Ciencias Agronómicas, Departamento de Sanidad Vegetal, Santiago 8820808, Chile; third author: Servicio Agrícola y Ganadero, Laboratorios y Estaciones Cuarentenarias, Santiago 9020000, Chile; sixth author: Council for Agricultural Research and Analysis of Agricultural Economics (CREA), Research Centre for Olive, Fruit Trees and Citrus, Roma 00134, Italy; seventh and eighth authors: Universidad Andres Bello, Facultad Ciencias Biologicas, Centro de Biotecnologia Vegetal, Santiago 8370146, Chile; eighth author: FONDAP Center for Genome Regulation, Santiago 8370146, Chile; and ninth author: Universidad de O'Higgins, Instituto de Ciencias Agronómicas y Veterinarias, Rancagua, 2820000, Chile.
Published: May 2018
AI Article Synopsis
Article Abstract
Kiwifruit bleeding sap samples, collected in Italian and Chilean orchards from symptomatic and asymptomatic plants, were evaluated for the presence of Pseudomonas syringae pv. actinidiae, the causal agent of bacterial canker. The saps were sampled during the spring in both hemispheres, before the bud sprouting, during the optimal time window for the collection of an adequate volume of sample for the early detection of the pathogen, preliminarily by molecular assays, and then through its direct isolation and identification. The results of molecular analyses showed more effectiveness in the P. syringae pv. actinidiae detection when compared with those of microbiological analyses through the pathogen isolation on the nutritive and semiselective media selected. The bleeding sap analyses allowed the isolation and identification of two hypersensitive response (HR) negative and hypovirulent P. syringae pv. actinidiae strains from different regions in Italy. Moreover, multilocus sequence analysis (MLSA) and whole genome sequence (WGS) were carried out on selected Italian and Chilean P. syringae pv. actinidiae virulent strains to verify the presence of genetic variability compared with the HR negative strains and to compare the variability of selected gene clusters between strains isolated in both countries. All the strains showed the lack of argK and coronatine gene clusters as reported for the biovar 3 P. syringae pv. actinidiae strains. Despite the biologic differences obtained in the tobacco bioassays and in pathogenicity assays, the MLSA and WGS analyses did not show significant differences between the WGS of the HR negative and HR positive strains; the difference, on the other hand, between PAC_ICE sequences of Italian and Chilean P. syringae pv. actinidiae strains was confirmed. The inability of the hypovirulent strains IPV-BO 8893 and IPV-BO 9286 to provoke HR in tobacco and the low virulence shown in this host could not be associated with mutations or recombinations in T3SS island.
