Metla Project 7025

Aspen research

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Duration: 1999-2003   Keywords: Hypoxylon canker, Neofabraea canker, aspen, hybrid aspen, shoot blight

Objectives

The biology and population structure of the pathogens of aspen and hybrid aspen will be studied in order to analyse their effect on forest cultivation.

Results

Symptoms typical of Neofabraea populi infection have been identified from hybrid aspen stands in southern Finland. Morphology of the fungal isolates in vitro and ascospores released from apothecia on cankers were compared with reference isolates and literature, respectively. A damage inventory was made in five stands. The percentages of healthy, diseased and dead stems per stand were calculated. The disease caused remarkable losses within stands (up to 53% mortality). Random amplified microsatellite markers were amplified from single-ascospore isolates, isolates from wood tissue and three reference isolates of N. populi. Both morphological and molecular analyses confirmed that the causal agent was N. populi as suspected. The results imply that this fungus may become a major problem in hybrid aspen plantations in southern Finland.

Entoleuca mammata isolates collected from Europe and North America were compared by sequence analysis of two DNA markers derived from DNA fingerprints. The objective of the study was to elucidate the relationship between North American and European E. mammata populations to test the hypothesis that the fungus was introduced to Europe from North America using phylogenetic analysis. North American populations were found to be more polymorphic in the analysis, but no major phylogenetic differences between fungal isolates collected from different continents were found. This result combined with the historical observations of the disease in Europe implies that E. mammata was introduced to Europe several centuries ago.

Genetic variation in three multiallelic loci was analysed with Temperature Gradient Gel Electrophoresis in order to assess the genetic population structure of Venturia tremulae var. tremulae in order to understand the evolutionary potential of the pathogen against resistance breeding. Also the identification of the fungus was verified with molecular analysis of reference isolates. The Fst and Gst values were very low indicating no substructuring or restrictions to gene flow between Fennoscandian populations of V. tremulae. The results imply high epidemiological efficiency and evolutionary potential of the fungus and therefore local background inoculum might be used in resistance screening trials.

Project leader: Kasanen, Risto

Other researchers: Hallaksela, Anna Maija, VA (1999-2000), Hantula, Jarkko, VA (1999-2001,2003), Kurkela, Timo (1999-2002), Vuorinen, Martti, SU (1999-2003)


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Updated 12.06.2012
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