Metla Project 3299

Aetiology and epidemiology of forest diseases

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Duration: 2000-2006   Keywords: Cronartium, Gremmeniella abietina, Phytophthora cactorum, Picea, Pinus, Sirococcus conigenus, disease dispersal, forest health, fungal diseases, silver birch, uninucleate Rhizoctonia
Research project group: Distinct projects 1 - Structure and function of forest ecosystems


The main objective of this study is to gain new knowledge about the effects of environmental factors on the condition and disease resistance of forest trees, on pathogens and their occurrence. In different parts of the project the objectives are as follows: 1) Abiotic diseases. Especially in northern Finland, dynamics of abiotic diseases will be studied, including the importance of exceptional weathers in the development of injuries and the connection between the abiotic and biotic diseses. The aim of the study is to elucidate the importance of abiotic diseases for forest health in Lappland where the forests are growing in their climatic extremities. 2) Cronartium epidemics; the causes of resintop epidemics. New basic knowledge will be gained about the causal agents, their virulence and about the factors affecting the disease resistance. The importance of Melampyrum species as alternate hosts will be studied. 3) The dispersal of forest pathogens and susceptibility in trees. Amounts of secondary metabolities in pine are compared to the scleroderris canker resistance. Interaction between nutrition, climatic factors, provenances and disease appearance will be studied. In that sence, objectives are Gremmeniella and Lophodermella on pines and Thekopsora on spruce as well as some in birch inhabiting fungi. Spore dispersal of some pathogens are also studied. Spore dispersal monitoring will be developed for forest nurseries


The pathogenicity of Cronartium flaccidum was tested on Melampyrum spp. and Vincetoxicum hirundinaria provenances resulting from artificial seeding or transplanting by inoculating the plants in the greenhouse. As the main result, C. flaccidum uredinia and telia were formed on leaves of Melampyrum nemorosum. This is the first time, as M. nemorosum has been inoculated resulting in successful disease establishment, and thus, the capability of the rust to use M. nemorosum as its alternate host was proved.

Susceptibility of Pinus sylvestris provenances from northern Finland and lesion development caused by Peridermium pini were investigated by inoculations. The disease incidence varied within the range of 0-9.4 % among pine provenances and 3.4-3.9 % among spore sources in 1994-2002. Annual fresh swellings were observed for 1-6 years and aecia for 2-9 years after inoculation. Spermatial fluid was observed in the year prior to aecia development. The results showed that tested pines were highly resistant to P. pini.

The relative susceptibility of four Melampyrum species (M. arvense, M. pratense, M. sylvaticum and M. nemorosum) to C. flaccidum was also investigated by whole-plant inoculations in the greenhouse. Uredinia and telia were formed variably on all host provenances. The results suggest that M. arvense and M. sylvaticum are the most susceptible species, while M. pratense is the most resistant one. This is the first report of artificial C. flaccidum uredinia and telia production on M. arvense. As an earlier unreported phenomenon, telia were formed on both upper and lower leaf surfaces of Melampyrum spp.

An uninucleate Rhizoctonia sp. causes a root dieback on Norway spruce and Scots pine seedlings in forest nurseries. Primers specific to this pathogen were designed, and they yielded an amplification product from mycelial cultures only when uninucleate Rhizoctonia sp. was used as a template. Inoculated Norway spruce and Scots pine seedlings with visible symptoms gave a clear and reproducible band. The same band appeared also from Norway spruce seedlings growing in inoculated peat or compost but lacking conspicuous symptoms. One of the benefits of the DNA based test was its higher sensitivity compared to the traditional isolation. The results are also available more quickly

The conidial dispersal of Gremmeniella abietina was studied using spore traps. Cumulative number of conidia increased linearily with logarithm of temperature sum. A binary logistic regression model with temperature sum and rainfall as explanatory variables predicted accurately the date of the first spores in the spring: the predictor error was at most 3 days. The conidia dispersal started in Suonenjoki, in 1997-99 by the end of May or beginning of June, and continued at least to the middle of September.

During the last few years a new type of disease has occurred on container Norway spruce in forest nurseries. The first sign of the disease is browning of needles, after which the needles may fall off and lesions develop on stems. In this study we analyzed the fungal community of cankers by both traditional isolation procedures and PCR-based methods. In 18S rDNA profiling several species (OTUs) were shown to live in the cankers, some of which could be linked to mycelial cultures of isolated fungi based on the identical mobilities in DGGE and sequencing. In further analyses the most common fungus proved to be Sirococcus conigenus. This is the first report on this pathogen in Finnish forest nurseries.

Project leader: Lilja, Arja
The Finnish Forest Research Institute, Vantaa Unit, PL 18, FI-01301 VANTAA, FINLAND
Phone: +358 29 532 5102

Other researchers: Hamberg, Leena (2002), Hantula, Jarkko, VA (2003-04), Jalkanen, Risto, RO (2002), Kaitera, Juha, MU (2002-06), Kurkela, Timo (2002), Nevalainen, Seppo, JO (2002-06), Nuorteva, Heikki, VA (2002-06), Pennanen, Taina, VA (2006), Petäistö, Raija-Liisa, SU (2002-06), Vartiamäki, Henna, VA (2002), Vuorinen, Martti, SU (2002-06)

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Updated 12.06.2012