Pathogenicity and sporulation of Phytophthora pinifolia on Pinus radiata in Chile
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Phytophthora pinifolia causes the needle and shoot disease of Pinus radiata known as Daño Foliar del Pino (DFP) in Chile. The first pathogenicity trials with this organism utilized mycelial plugs placed on stem wounds. These resulted in lesions in the tissue, but did not reproduce the resinous bands on the needles, which are the most characteristics symptoms of the disease under natural conditions. In this study, stem inoculations were repeated, but to complete Koch’s postulates fully, and to confirm that P. pinifolia causes the symptoms observed on naturally infected trees, zoospore/sporangial suspensions were used to inoculate pine foliage. This method produced the same symptoms observed on needles infected naturally. These results confirm that P. pinifolia is the causal agent of the Daño Foliar del Pino on P. radiata in Chile and successfully completed Koch’s postulates for the first time. Pathogenicity tests on different Pinus spp. and hybrids showed a wide range of responses to inoculation with P. pinifolia mycelial plugs, from highly susceptible to resistant. Monitoring of sporulation revealed that the sporangia commonly remain on the needles for extended periods of time and their frequency of occurrence and dispersal appear to increase during the rainy season.
KeywordsDaño Foliar del Pino Phytophthora pinifolia Pinus radiata Needle disease Sporulation monitoring
We thank Bioforest S.A. and Bosques Arauco, subsidiaries of Arauco Group for their financial and technical support. We also thank various colleagues including Mr Rolando Gómez, Mr Rafael Quezada, Mr Rodrigo Nova, Dr Alvaro Durán, Mrs Carolina Valiente and Mr Boris Palma for their commitment in the field and laboratory work together with the Lab workers. Mrs Marcela Millar and Mr Iván Appel to provide the Pinus species tested. Mr Eduardo Rodríguez and Dr Claudio Balocchi, for useful discussions that have assisted us in completing this study. We also thank Mrs Seonju Marincowitz from University of Pretoria and Mr Freddy Mora from Universidad de Concepción for their support and help with microscope measurements and statistical analyses, respectively.
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