Kiwi bacteriosis - increased virulence compared to 2010

Over the past few years, kiwi bacteriosis - caused by Pseudomonas syringae pv. actinidiae (Psa) - generated significant economic losses for what concerns both yields and fruit quality.

Pathologists from the Department of Agricultural, Forestry and Food Sciences (Disafa) and the Centre for Agricultural and Environmental Innovation (AGROINNOVA) at the University of Turin analysed the bacteria strains identified in kiwi orchards in northern (Piedmont) and central (Lazio) Italy both during the first serious episode (2008-2010) as well as a few years later (2014), when the pathogen had become endemic.

Disease indexes to assess the virulence of Pseudomonas syringae pv. actinidiae strains inoculated on plants and Actinidia chinensis var. Deliciosa 'Hayward' leaf disks.

The research team assessed both the genetic differences of six housekeeping and effector genes as well as the in vitro/in vivo virulence on the same strain. The analyses showed a higher disease index for the strains isolated in 2014 compared to 2010. Molecular fingerprinting revealed a high level of variability of the Pseudomonas syringae pv. actinidiae strain populations from Piedmont orchards.

Three populations were identified:

Piedmont 2010 made up of 12 strains;
Piedmont 2014 made up of 21 strains;
Lazio made up of 5 strains.

"All parameters showed a higher genetic diversity within the population of northern Italy isolated in 2014 compared to that isolated in 2010. The study of genetic diversity and virulence showed an increase of the virulence and genetic diversity of the strains. The fast and dramatic epidemic caused by Pseudomonas syringae pv. actinidiae could constitute an interesting model to study the changes in genetic diversity and virulence of phytopathogenic bacteria."

Source: Simona Prencipe, Maria Lodovica Gullino, Davide Spadaro, 'Pseudomonas syringae pv. actinidiae isolated from Actinidia chinensis Var. deliciosa in Northern Italy: genetic diversity and virulence', Giugno 2017, European Journal of Plant Pathology.