The results are relevant for taxonomy of isolates of P. syringae from kiwifruit, especially those of low virulence not belonging to pathovar actinidiae.
Bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), is a disease that is spreading rapidly in several kiwifruit‐producing countries, causing significant economic losses. In 2011, it was detected for the first time in Spain, in the south of Galicia (northwest Spain). Kiwifruit orchards were therefore inspected and sampled in 2011 and 2012 to determine the pathogen distribution, and the isolates obtained were characterized by morphology, fatty acids profile, biochemical tests and molecular techniques. Isolates were obtained from Actinidia deliciosa ‘Hayward’ (from leaves, canes, flower buds, fruits and roots), from A. deliciosa ‘Summer’, from Actinidia chinensis ‘Jin Tao’ (from canes and leaves) and from A. chinensis pollinator ‘Belén’ (from canes). Results of the analysis of the cfl gene (phytotoxin production‐related), the tox–argK gene cluster and phylogenetic analysis of the cts gene demonstrated that all Psa isolates from northwest Spain correspond to the Psa3 population, which includes strains of haplotype 2. This is the first record of Psa3 and haplotype 2 in Spain.
The pandemic Pseudomonas syringae pv. actinidiae (Psa) has been compromising the production of the kiwifruit industry in major producing countries. Abiotic factors and plant gender are known to influence the disease outcome. To better understand their impact, we have determined the diversity of the leafs bacterial communities using the V5-V6 region of the 16S rRNA gene amplicon on the Illumina MiSeq sequencing platform. Healthy and diseased female and male kiwifruit plants were analyzed in two consecutive seasons: spring and autumn. This work describes whether the season, plant gender and the presence of Psa can affect the leaves bacterial community. Fifty bacterial operational taxonomic units (OTUs) were identified and assigned to five phyla distributed by 14 different families and 23 genera. The leaves of healthy female and male kiwi plants share most of the identified bacterial populations, that undergoes major seasonal changes. In both cases a substantial increase of the relative abundance of genus Methylobacterium is observed in autumn. The presence of Psa induced profound changes on leaves bacterial communities structure translated into a reduction in the relative abundance of previously dominant genera that had been found in healthy plants, namely Hymenobacter, Sphingomonas and Massilia. The impact of Psa was less pronounced in the bacterial community structure of male plants in both seasons. Some of the naturally occurring genera have the potential to act as an antagonist or as enhancers of the defense mechanisms paving the way for environmentally friendly and sustainable disease control.
Pseudomonassyringae pv. actinidiae (Psa) is a gram-negative bacterium responsible for the bacterial canker in Actinidia chinensis var. deliciosa and A. chinensis var. chinensis, a quarantine organism threatening the kiwifruit industry sustainability. The present study aimed to determine the genetic structure of the endophytic and epiphytic populations of Psa isolated from four different Portuguese orchards with distinct abiotic conditions in two consecutive seasons. The results identified several coexisting and highly heterogeneous Psa populations. Moreover, evident changes in population structure occurred between the epiphytic and endophytic populations, and between seasons with a notable decrease in Psa diversity in autumn. This work provided solid evidence that the initial clonal expansion of Psa in Europe was followed by a wide genomic diversification. This perspective is important for the understanding of kiwifruit bacterial canker disease occurrence and Psa evolution, namely when adopting strategies for management of epidemics.
Aims
Bacterial kiwifruit canker disease, caused by Pseudomonas syringae pv. actinidiae (Psa) was detected in north‐west Portugal in 2010, and has since caused significant losses. The objectives of this work were to characterize the Portuguese population(s) of Psa and to define the actual prevalence of Psa biovars in the most productive kiwifruit region in Portugal.
Methods and Results
Isolates obtained from Actinidia deliciosa orchards were characterized by morphological, biochemical, physiological, fatty acids and molecular tests (PCR, BOX‐PCR, duplex‐PCR, multiplex‐PCR and RFLP), phaseolotoxin, housekeeping and effector genes and pathogenicity. Results established that only Psa biovar 3 is present in the north‐west of Portugal, despite phenotypic and genetic variability among the isolates.
Conclusions
This work provides new information on P. syringae pv. actinidiae (Psa) genetic profile in Portugal, indicating for the first time, that two genetically different subpopulations of Psa biovar 3 are present.
Significance and Impact of the Study
A new subpopulation of Psa biovar 3 was found for the first time in Portugal, contributing to increase knowledge about this population worldwide and to support further understanding of the impact of Psa.
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