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According to recent statistics, in Italy a significant spread of the bacterial canker of Actinidia caused by Pseudomonas syringae pv. actinidiae (Psa) is recorded with peaks of 70 and 100%, and lower percentages ranging around 50%. The control of the Psa is a priority especially considering the hazard represented by the endophytic bacterial presence in nursery material. To evaluate the risk that could be associated with micropropagated shoots when using asymptomatic mother plants, Psa survival was studied in micro-propagated shoots of A. deliciosa 'Hayward' inoculated with different concentrations of a virulent Psa gfp-expressing/rifampicin-resistant strain (Psagfp-Rif(res)). Microbiological and molecular analysis were carried out at each in vitro transfer and on rooted plantlets in greenhouse. The Psagfp-Rif(res) reisolation on selective media confirmed by PCR analysis and by the ability to induce symptoms in Actinidia and HR in tobacco plants, was achieved in both the micropropagated materials and in the plants analyzed in toto after their re-establishment. A reliable and efficient method for Psa detection in nursery material is proposed to verify the presence Psa infection before symptom development.

Italy is one of the largest producers of Kiwi [Actinidia deliciosa (Chev.) Liang & Ferguson] and cv. Hayward is the most widespread. Over the past 10 years, especially in Northeastern and Central Italy, there was an increase in the cultivation of yellow kiwi (Actinidia chinensis Planchon) in which symptoms of bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) have been reported in cultivations in the Lazio region. In Japan, China and Korea, major economic losses were caused by this bacterial disease that seriously damages all vegetative organs of the plant. The development of reliable diagnostic methods for asymptomatic materials is crucial for the activity of Plant Protection Services in order to confirm the presence of the pathogen in the territory and in marketing materials. Bacteria isolation from the fruits surface (31 samples cv. Hayward from Emilia Romagna region) and from their asymptomatic columellae to detect the presence of Psa was performed. As for the bacteria identification the following tests were carried out: fluorescent pigment production, HR in tobacco leaves, oxidase activity, acid production from sugars and molecular analysis (PCR-RFLP, REP-, BOX-PCR and Bio-PCR). The identification assays of the isolates obtained from the surface and columella fruits of all samples were negative for Psa. In order to discriminate Psa from the other kiwifruit pathogenic bacteria (i.e. Pseudomonas syringae pv. syringae and Pseudomonas viridiflava) and to confirm the isolates identification, the Psa pathogenicity was tested in fruits and kiwifruit plantlets. Moreover, Psa lives in the phyllosphere together with non-pathogenic bacteria that may interfere in the diagnosis of the bacterial canker by means of false negative or positive results. Therefore, from leaves and shoots of asymptomatic plants of Actinidia chinensis Hort 16A and Actinidia deliciosa cv. Hayward, collected from the Emilia Romagna region, epiphytic bacteria were isolated and studied.

During 1997, in occasion of the severe epidemic caused by Erwinia amylovora (Ea) on pear-tree in Emilia-Romagna, the first certified cases of fire blight were also reported in Veneto. Of the 14 ascertained foci, 11 were found in Rovigo province, ie. in areas facing the northern border of Emilia-Romagna and 2 were found in Padua and Verona provinces. In the following two years, the territorial distribution of the new foci in Verona, Padua and Venice provinces clearly pointed out that from Venetian areas close to the border with Emilia-Romagna the Ea was spreading mostly towards the north-west. In this study, the AFLP genomic analysis of 14 isolates from pear-tree showed that all Venetian isolates were referred to the same clone originally coming from Emilia-Romagna. After 1997 in Emilia-Romagna there has been a substantial increase in the official cases of fire blight on host plants other than pear-tree. From the clonal lineage of Ea, introduced in 1994, may originate secondary lines different for pathogenic traits selected by the new host plant or a new clonal lineage could have occurred. The AFLP of the Ea strains isolated from host plants other than pear-tree was carried out in order to study the genetic variability between the Emilian strains which were found to belong to the original clone. Moreover, to test the hypothesis of continuity of the original clonal lineage, the changes of the virulence grade among the strains was studied. The pathogenicity test on immature pear fruitlets was performed measuring the minimum/maximum axis of the lesion induced by each strain (14 Venetian and 47 Emilian strains). The strain OMP-BO1077/7, associated to the primary foci in Emilia-Romagna on pear during 1994, was used as a reference strain. For each strain the virulence index was calculated and statistical analysis was used to determine the significant difference with the reference strain