Zusammenfassungen der Arbeitskreisbeiträge - Die DPG

liquid inoculum results in a homogeneous disease incidence, becoming an accurate alternative
to solid inoculum due to the fact that it enables the quantification of the amount of mycelium
used to inoculate single plants. A direct contact among the plant and the inoculum accelerated
the disease process reducing the number of escapes. A concentration of 4 mg of R. solani
mycelia per ml water applied near to the beet crown was sufficient to generate homogeneous
disease incidence. Higher disease incidence of Rhizoctonia solani AG 2-2IIIB and AG 4 was
evident when younger plants were inoculated. Four weeks was the optimum plant age to
inoculate sugar beet plants in order to generate R. solani infection since at this time no
escapes were present.
PHYTOPHTHORA ROOT ROT OF BUXUS SEMPERVIRENS IN BAVARIA,
POSSIBLY CAUSED BY THE NEW SPECIES PHYTOPHTHORA HIMALSILVA
Wolfgang W.P. Gerlach 1 , Roland Schubert 2 , T. Lehneis 1
1 Forschungsanstalt für Gartenbau Weihenstephan an der Hochschule Weihenstephan-
Triesdorf, 85350 Freising,Germany
2 Hochschule Zittau/Görlitz, 02763 Görlitz, Germany.
Contact: wolfgang.gerlach@hswt.de
Repeatedly we received cuttings of Buxus sempervirens with root rot, which originated from
Rumania, starting 2006 and subsequently also we received diseased boxwood plants from a
nursery from near Landshut, Bavaria. The plants showed distinct root rot and stem rot, which
was accompanied by partial or complete browning of branches and leaves. From all plants we
could isolate on a selective medium Phytophthora cultures. These isolates could not be
matched with any known species. The sporangia showed a certain similarity to P.
citrophthora. In our isolates the sporangia were ovate to pyriform, with a distinct papilla and
average sizes of 43.8 �m ��26.1 �m. About 10% of the sporangia displayed a bent shape
(mouse shape), as can be found occasionally with pear fruits. Generally the sporangia showed
a very variable shape and size. Quite distinctly, all the isolates were homothallic, with
aplerotic oogonia of a mean diameter 28.2 �m growth and curve paragynous antheri
indicated a minimal growth at 5°C, optimal growth at 25°C and an upper growth limit at
35°C. Preliminary comparisons of genomic sequences and phylogenetic analyses indicated
that our isolates were closely related, if not identical to the just recently published new species
of Phytophthora himalsilva Vettraino, Brasier & Vannini, which was known to occur only in
Nepal. Further investigations are in progress.
References
Vettraino AM, Brasier CM, Brown AV & Vannini A, (2011). Phytophthora himalsilva,
sp.nov. an unusually phenotypically variable species from a remote forest in Nepal.
Fungal Biol 115, 175-287.
OPTIMAL CONDITIONS FOR THE PRODUCTION OF PSEUDOTHECIA AND
THE DISCHARGE OF ASCOSPORES OF VENTURIA INAEQUALIS
Beatriz Lauria-Pluschkell, Hans Scheinpflug, Ulrike Steiner
INRES – Phytomedizin, Nussallee 9, 53115 Bonn, Germany.
Contact: wolfgang.gerlach@hswt.de; beju.home@googlemail.com
Venturia inaequalis is undoubtedly one of the most studied fungi, but there are still many
questions not answered. An easy and efficient method that allows not only to get ascospores
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