Homogeneity of European PSA strains

After the first report of PSA in 2010 (Balestra et al., 2010. First report on bacterial canker of Actinidia deliciosa caused by Pseudomonas syringae pv. actinidiae in Portugal. New Disease Reports 22, 10) and some suspected symptoms recorded in early 2011, the group of phytobacteriology at DAFNE, University of Tuscia in Viterbo (Italy) has developed an extensive survey on PSA in all areas of Portugal where kiwifruit plants are cultivated.

Natural symptoms caused by Pseudomonas syringae pv. actinidiae on flowers of Actinidia chinensis cv. ‘Soreli’ (a) and leaf of cv. ‘Belen’ (b), and on a leaf of A. deliciosa cv. ‘Hayward’ (c), buds of cv. ‘Bo Erica’ (d) and a twig of cv. ‘Summer’ (e).

The study, supported in part by the Department of Agriculture of the Region of Lazio, and carried out with the collaboration of the Associação Portuguesa de Kiwicultores (APK) of Portugal and Dr. V. Araujo and M. Bovo, had the purpose of verifying the effective dissemination and incidence of the bacterial disease, such as to study the genetic characteristics of the population of PSA found in Portugal.

Numerous inspections, samplings and subsequent analysis were made during the entire 2011 season.

On the right: A map of Portugal showing the kiwifruit areas investigated and recordings of Pseudomonas syringae pv. actinidiae in order of time for the main production areas:
1) Valença (2010, 2011);
2) Lago Braga;
3) Quinta dos Bocas;
4) Felgueiras;
5) Vila boa de Quires;
6) Santa Maria Da Feira (2011).

The results confirmed the widespread presence of the pathogen in the main kiwifruit production areas of Portugal, on different species/cultivars of Actinidia, with an incidence ranging from 30% to 85% or more.

Genetic analysis showed that all isolates of PSA analyzed belong to the European genotype, confirming the results recently published (Mazzaglia et al., 2012: http://dx.plos.org/10.1371/journal.pone.0036518).

The genetic homogeneity of PSA European strains, despite the multiple nature of the geographical areas where the pathogen was isolated, suggests that the disease, at least as regards the epidemic from 2008 onwards in Europe, has a common origin.

Comparison of results obtained by MLST (left) and fingerprint (right) analyses on 20 Portuguese Pan strains selected for molecular investigation and on reference strains. Click here to enlarge.

The results seem to confirm the fact that Portugal is simply one of the last frontiers achieved by the current PSA European epidemic that, in a few years, was found in almost all most important areas of the European Union where the cultivation of Actinidia plants and the production of kiwi fruits are of economic importance.

It is also clear that the rapidity of the spread (associated with the uniformity of the PSA strains), is probably due to the spread of infected plant material, the lack of knowledge of symptoms determined by this bacterial pathogen, as the lack of appropriate and preventive control strategies.

Therefore, the results obtained during these investigations seem to suggest the need to use only propagation material properly certified as PSA free.

The study was recently published in the scientific journal Phytopathologia Mediterranea (Authors: M. Renzi, A. Mazzaglia and Balestra G.M., title: Widespread distribution of kiwifruit bacterial canker caused by the European Pseudomonas syringae pv. actinidiae genotype in the main production areas of Portugal. Phytopathologia Mediterranea 51, 2, 402-409).

Contact
Dr. Giorgio M. Balestra – Senior Researcher
DAFNE (Dep. of Agriculture, Forestry, Nature and Environment)
University of Tuscia
Via S. Camillo de Lellis
01100 Viterbo (Italy)
Phone: +39 (0)761 357474
Fax: +39 (0)761 357473
Email: balestra@unitus.it
Personal Web: www.agraria.unitus.it/interna.asp?idCat=244