Association levels between Pityophthorus pubescens and Fusarium circinatum in pitch canker disease affected plantations in northern Spain
Bezos, Diana; Martínez-Álvarez, Pablo; Diez, Julio J.; Fernández, Mercedes
Abstract Fusarium circinatum, the causal agent of pitch canker disease (PCD), poses a threat to Pinus radiata plantations due to the presence of bleeding cankers on the trunk that can cause the tree to die. This pathogen has been reported to be phoretically associated with bark beetle species, specifically, with Pityophthorus species in California. Pityophthorus pubescens is a secondary pest, attacking weak trees or broken branches in healthy trees. The aim of this study was to know the association between P. pubescens and F. circinatum in PCD affected plantations in northern Spain. Specific aims were determined: i) to assess the phoretic association between P. pubescens and F. circinatum, ii) to study the presence of F. circinatum in P. pubescens infested twigs and iii) to evaluate whether PCD damages were enhanced in (E)-pityol baited P. radiata trees. Funnel traps baited with (E)-pityol were established and twigs from infested trees were sampled to collect insects and plant tissues in PCD affected plots, with the aim of testing the presence of F. circinatum. Moreover, an experiment was carried out in nature in which P. radiata trees were baited with (E)-pityol and PCD symptoms were evaluated 4 times during one year. A total of 263 specimens were collected from funnel traps between June and September 2010, 2011, 2012 and 2013. Moreover, 215 specimens were collected from 424 galleries within the twigs in 2012 and 2013. The pathogen appeared on 1.05% and 2% of the insects in the funnel traps during 2010 and 2012 respectively. Regarding the collected twigs, F. circinatum was found in 3 galleries, whilst results of the baiting experimentation showed symptoms in the crown were more influenced by (E)-pityol than those on the trunk. This work affirms a weak association between P. pubescens and F. circinatum in our study area.