Pseudomonas syringae pv. Actinidiae isolated from non-kiwifruit plant species in China

Kiwifruit bacterial canker (KBC), incited by Pseudomonas syringae pv. actinidiae (Psa), may cause severe economic losses to kiwifruit (Actinidia deliciosa and A. chinensis). Many studies have been conducted to clarify relationships between this pathogen and Actinidia species. Conversely, little is known about the chance to colonize alternate hosts and the implications of this possibility on disease spread. In this study, 11 bacterial isolates have been isolated from three wild plant species, Setaria viridis (L.) Beauv., Alternanthera philoxeroides (Mart.) Griseb. and Paulownia tomentosa (Thunb.) Steud., found under or nearby kiwifruit plants affected by bacterial canker. All were identified as Psa based on biochemical tests, specific end-point PCR assays, sequence analysis of single effector genes and MLST. The strains tested positive for pathogenicity, both on wild hosts and on kiwifruit plants. To our knowledge, this is the first report on Psa isolated from non-kiwifruit plants. The proof that Psa can migrate to non-kiwifruit plants raises new issues about the means by which the disease can spread at local and international scales, and the measures to be taken to prevent and control effectively KBC disease.