Detection of Possible Phytophthora pinifolia Infection in Pinus radiata Green Sawn Timber Produced in Chile

A new needle blight disease was observed on Pinus radiata in Chile during 2004. The disease, known in Chile as Daño Foliar del Pino (DFP), stretches southward from the Arauco to Valdivia Provinces, and was present over an area of about 60 000 ha in 2006, with different levels of intensity. The disease is typified by needle infections and exudation of resin at the bases of the needle brachyblasts. Only P. radiata trees have been affected by DFP. Other Pinus species in the area, such as P. pinaster, remain healthy. Isolations from infected needles on selective media have consistently yielded a Phytophthora sp. DNA sequence comparisons for the ITS rDNA and cox II gene regions, and morphological observation, showed that this oomycete represents a previously undescribed species, which has been named Phytophthora pinifolia (Durán, Gryzenh, and M.J. Wingf). Research is underway to fully elucidate the life cycle of P. pinifolia and to develop appropriate management strategies on Chilean pine plantations. Despite being an aggressive pathogen and an aerial Phytophthora, P. pinifolia is phylogenetically closely related to other Phytophthora spp. that are mildly pathogenic and normally associated with soil and roots. Pathogenicity trials with P. pinifolia have clearly shown that it is pathogenic to P. radiata and causes rapid death of the succulent apical parts of young plants. P. pinifolia is the first Phytophthora sp. known to infect needles of a Pinus sp. and its aerial habit is well-matched with the occurrence and symptoms of DFP in Chile. To understand the behavior of P. pinifolia in green timber, a study was conducted to determine the possible presence of P. pinifolia in green sawn timber produced from trees that had been exposed to infection by the pathogen for at least 4 years. Green timber from the infected trees, and green wood samples exposed to P. pinifolia inoculum, were analyzed by making extensive isolations on Phytophthora-selective media. In addition, fluorescence microscopy was used to observe the possible presence of structures of the organism and PCR was conducted using species-specific primers developed for P. pinifolia. Results of the study showed that the green sawn timber taken from trees infected by P. pinifolia, or even green timber exposed to contaminated pine plantations, showed no evidence that the pathogen can survive or develop in green wood. These results provide strong evidence that green sawn timber produced from P. radiata trees infected with P. pinifolia is free of the pathogen and that it can be exported safely without any specific treatment against P. pinifolia. 1 A version of this paper was presented at the Fourth Sudden Oak Death Science Symposium, June 1518, 2009, Santa Cruz, California. 2 Bioforest S.A., Concepción, Chile. 3 Servicio Agrícola y Ganadero, Chile. Corresponding author: [email protected]. Proceedings of the Sudden Oak Death Fourth Science Symposium