sdu faculty of forestry journal special edition 2009 - Orman Fakültesi

SDU Faculty of Forestry Journal
Serial: A, Number: Special Issue, Year: 2009, ISSN: 1302-7085, Page: 265
GREMMENIELLA INFECTIONS ON SEEDLINGS AFTER
REPLANTING SEVERELY INFECTED PINE FOREST
Elna STENSTRÖM 1* , Maria JONSSON 1 , Kjell WAHLSTRÖM 1
1 Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences,
Uppsala, Sweden
*elna.stenstrom@mykopat.slu.se
During 1999 and 2001 the most severe Gremmeniella abietina epidemic ever
appeared in Sweden. More than 300 000 ha forest were severely attacked and the
forest industry lost milliards of SEK. Big forest areas, with at least 50 000 ha,
needed to be clear cut in advance followed by replanting.
For the out-planting experiment pine seedlings were planted on three different
locations in Dalarna in Sweden, that were clear-cut in advance due to severe
Gremmeniella infection. The forest had been clear-cut in 2001 and this study was
conducted during 2002-2005. Each site contained one clear cut area and a nearby
Gremmeniella infected forest. Seedlings were planted on clear-cut areas with and
without remaining twigs and branches, at the edge of the clear-cut areas, as well as
in the adjacent forest. In total at least 200 seedlings were planted on each area. The
areas were replanted every year with new one year old seedlings received from a
forest nursery. The disease incident was determined visually the year after
plantation and then the infection was confirmed with PCR using Gremmeniella
specific primers.
For seedling planted at the clear cut areas, the infection decreased from 50 -
90% infected seedlings planted one year after felling to 0 - 55% planted the second
year after felling and to 0 -38% for seedling planted three years after felling. After
four years there was almost no infection on the clear-cut areas. The variation was
big between the sites. Two and three years after felling there were almost no
differences between seedlings planted on areas with or without twigs and branches.
However seedling planted in the adjacent diseased forest became much more
infected then seedlings planted on the clear cut areas. For seedlings planted in the
forest one year after felling almost all seedlings became infected. Two and three
years after felling they became infected to up to 50 % and even four years after
felling 15-40 % of the seedlings became infected. The seedlings planted close to
the forest edge were always more infected then the seedlings out on the clear-cut
areas but less infected than the seedlings in the forest.
It is remarkable that the disease incidence on seedlings in the forest still is high
after 3-4 years but we assume that the snow cover during winter have promoted the
infections in small seedlings. From inventory in mature forest in the same areas it
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