Pseudomonas syringae pv. actinidiae (PSA): diagnosis, detection, identification and study of epidemiological aspects (PSADID)

Pseudomonas syringae pv. actinidiae (Psa) is the causal agent of bacterial canker of kiwifruit. This pathogen affects Actinidia species (Actinidia deliciosa and A. chinensis) worldwide. The main symptoms are oozing of whitish or reddish exudates from cankers present along the trunk and branches, spots surrounded by yellow halos on the leaves, twig dieback, fruit collapse, leaf and plant wilting. The disease is a serious threat for kiwifruit production, due to high tree mortality and reduced production and, consequently, having an increasing socio-economic impact. The recent severe outbreaks of bacterial canker of kiwifruit in the European and Mediterranean Plant Protection Organization (EPPO) regions and in New Zealand has been related to the appearance of a local, very aggressive aplotype of Psa.called Psa biovar 3. Possible pathways of pathogen introduction and disease spread into new territories are Actinidia spp. plants for planting, which represent the main pathway for long distance dissemination of Psa. However, positive pollen samples were recovered in New Zealand and in Italy. Therefore, the possibility that infected pollen could be a pathway for Psa introduction and disease spread was investigated and confirmed (EPPO, 2012; Tontou et al., 2014). It was suggested that pollen, as a pathway, should be certified free from Psa (Zespri, 2012; EPPO, 2016). Other dissemination pathways are wind and wind driven rain, spring frost, equipment and tools. Recently an EPPO standard has been published as formal guidance on procedures for the detection of Psa (EPPO, 2014). Screening and identification methods are mainly based on conventional PCR (single and duplex PCR’s) (Rees-George et al., 2010, Gallelli et al., 2011a) and of repetitive-PCR (rep-PCR). Considering the worldwide high impact of this pathogen on kiwifruit, during the last few years several authors have developed new molecular methods (Biondi et al., 2013; Balestra et al., 2013; Gallelli et al., 2014). However, these latter methods need to be validated for their inclusion in the procedure for detection of Psa as screening and/or identification tests.

The project aims to develop innovative diagnostic tools to improve Psa detection and identification in symptomatic and symptomless kiwifruit plant material, including pollen and to improve the knowledge on the epidemiology of Pseudomonas syringae pv. actinidiae in different areas of Europe. In particular a test performance study will be organised to produce validation data for relevant detection methods to be used for the detection and identification of Psa on symptomatic and symptomless kiwifruit materials (leaves, pollen and wood tissues).