%0 Articles
%T Phytophthora in Finnish nurseries
%A Rytkönen, Anna
%D 2011
%J Dissertationes Forestales
%V 2011
%N 137
%R doi:10.14214/df.137
%U http://dissertationesforestales.fi/article/1920
%X Human-mediated movement of plants and plant products is now generally accepted to be the primary mode of introduction of pathogens and pests. Species of the plant-pathogenic genus Phytophthora are commonly spread in this way and have caused severe epidemics in silviculture, horticulture and natural systems all over the world. The objective of the study was to gather information on the occurrence of Phytophthora spp. in Finnish nurseries, produce information for risk assessments for these species, and establish molecular means for their detection. Phytophthora cactorum was found to persist in natural waterbodies and results suggest that irrigation water might be a source of inoculum for the disease in nurseries. Isolations from ornamental Rhododendron yielded three species new to Finland: P. ramorum, P. plurivora and P. pini. Phytophthora ramorum was able to persist in the nursery in spite of an annual sanitation protocol. Phytophthora plurivora and the closely related P. pini had had higher infectivity rates and more hosts among Nordic tree and plant species than P. ramorum and P. cactorum. All four species survived two weeks in -5 °C , and thus soil survival in Finland is likely under current climatic conditions. Picea abies was highly susceptible to P. plurivora and P. pini in pathogenicity trials. In P. abies shoot tissues inoculated with P. plurivora zoospores, fast necrotrophic growth was observed in nearly all tissues. In this study, a PCR–DGGE technique was developed for simultaneous detection and identification of Phytophthora spp. It reliably detected Phytophthora in plant tissues and could discriminate most test species as well as indicate multiple-species infections. All of the introduced species of Phytophthora had properties that promote a high risk of establishment in Finland. Due to transport via commercial traffic, it is probable that pathogens of this genus will be introduced and become established in Finland and other Nordic countries.