Early detection of Pseudomonas syringae pv. actinidiae from ‘bleeding sap’ in Chile

In Italy, during the boreal spring of 2012, a useful method was evaluated to detect the causal agent of kiwifruit bacterial canker (Pseudomonas syringae pv. actinidiae, Psa) from 'bleeding sap'. In Chile, during the austral spring of 2013, such method was applied to confirm its efficiency in Psa early detection and to evaluate the best sampling period in the austral hemisphere. Almost 30 bleeding sap samples were collected from asymptomatic plants located in two regions, in three different Psa-free fields. Microbiological and molecular analyses (nested PCR) were performed on collected bleeding sap samples to assay the presence of the pathogen in any field. Traditional sampling and analysis were also carried out on plant material collected from the same plants used for bleeding saps collection. The isolation of Psa was possible from approx. 20% total bleeding sap samples, while the detection of the pathogen using nested PCR directly on processed bleeding saps was achievable from more than 70%. When analysis on traditional samples was applied, ca. 30% total samples were found positive for the presence of Psa. During the next vegetative season only 15% part of the analyzed plants became symptomatic. Bleeding sap analysis revealed the presence of the pathogen in any of the three fields visited; the analysis on traditional samples confirmed those results. The analysis achieved in Chile on bleeding saps confirmed its efficacy in the early detection of Psa. The rapidity of the method may become useful in detecting latent infections.