Íslenskar landbúnaðarrannsóknir - 01.09.1982, Side 29

REYNIÁTA Á ISLANDI 27
SUMMARY
Cytospora rubescens Fr. ex Fr. in Iceland.
Halldór Sverrisson
Agr. Res. Institute Reykjavík, Iceland.
Rowan (Sorbus aucuparia L.) is one of the
most important garden tress in Iceland.
Lesions on the bark and dead branches are
frequently found on rowan, but the causes
of this were not known. Amoung the causes
that have been suggested are freezing
damage and the pathogens Nectria gal-
ligena Bres. and Cytospora rubescens Fr.
es Fr., but the pathogenicity of the latter
has been doubted. The aim oF this
investigation was mainly to get an idea of
the seriousness of bark damages in Iceland
and to identify the main cause.
Dead branches proved to be much more
common in Reykjavík in the south-west
partofthecountry, whereabout50% ofthe
trees have many dead branches. In
Akureyri in the north, however, only half
that number of trees were found to be
damaged.
HEIMILDARIT — REFERENCES
Bjarnason, H., 1979. Ræktaðu garðinn þinn.
Leiðbeiningar um trjárækt. Iðunn, Reykjavík.
Davíðsson, /., 1962. Gróðursjúkdómar og varnir
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Iceland, II, Pt. 3. pp. 449—607. ■
When fungus isolates and bacteria from
dead bark were tested for their ability to
grow on healthy bark, only Cytospora
rubescens proved to be parthogenic.
Eleven isolates of C. rubescens from
various plaves were tested for their growth
rate on bark, and there was significat
difference between the isolate with the
fastest growth (14,8 mm in 10 days) and the
one that grew most slowly (3,8 mm in 10
days, 20-25 C).
Bark from different individuals of
rowan, seemed to have very different
resistens to thegrowthofC. rubescens after
inoculation with the fungus.
The possibility for predisposing effect of
freezing and other climatic factors are
discussed.
Possible control methods are briefly
discussed. Cultivation ofresistentvarieties
ofS. aucuparia is considered the best way
to reduce this problem.
MacBrayne, C.B., 1981. Canker and dieback of
Sorbus spp. European Journal of Forest Patho-
logy 11:325—333.
Schulz, U., 1981. Untersuchungen zur biologischen
Bekámpfung von Cytospora-Arten. Zeitschrift
íúr Pflanzenkrankheiten und Pflanzenschutz
88:132—141.
Spielman, L.J., 1980. Cytospora vs. Cytispora:
which is correct? Mycotaxon 10:473—478.
Wene, E.G. & Schoeneweiss, D.F., 1980. Localized
freezing predisposition to Botryosphaeria can-
ker in differentially frozen woody stems. Cana-
dian Journal of Botany 58:1455—1458.