Book of Abstracts (PDF) - International Mycological Association

IMC7 Monday August 12th Lectures
of phytohormones in axenic culture. Although the impact
of this biosynthetic capacity on host-parasite interaction is
unclear, it has been suggested that production of the
phytohormone abscisic acid (ABA) is supporting the
infection process. A molecular approach has been initiated
to study the role of phytohormones in the pathogenicity of
B. cinerea. Our aim is to clone genes encoding enzymes of
the biosynthetic pathways, especially the ABA pathway, to
study their expression and to analyse the pathogenicity of
deletion mutants. Therefore, a cDNA library of an ABA
overproducing strain was established and differentially
screened. Several cDNA clones derived from genes
expressed during ABA production were characterised.
88 - Ethylene production and ethylene-induced genes in
Botrytis cinerea
V. Chague & A. Sharon *
Department of Plant Sciences Tel Aviv University, Tel Aviv
69978, Israel. - E-mail: amirsh@tauex.tau.ac.il
We defined the biosynthetic pathway of ethylene in the
pathogenic fungus Botrytis cinerea, and characterized the
conditions that affect ethylene production in vitro. During
the first 48 h of culture the fungus uses methionine to
produce a-keto g-methylthiobutyric acid (KMBA). In
darkness, KMBA accumulates in the medium and no or
very low ethylene levels are produced. In light KMBA is
photo-oxidized and ethylene is released. Ethylene
production rates in the light were the highest after 24 h (7
ml/g/h) and declined thereafter, whereas in the dark
ethylene was detected only after 48 to 96 h of culture. A
cDNA library was constructed from fungal mycelium that
was grown for 24 h in the light in methionine-enriched
medium. The library was differentially screened with
mRNA probes from light (ethylene +) and dark (ethylene -)
grown cultures. Over 20 differential clones were identified.
These clones represent transcription factors, glycolysis
enzymes, ribosomal proteins and unknown ESTs. Northern
hybridization was conducted to confirm the differential
expression pattern of the clones and to further define the
expression pattern of clones that were highly induced by
ethylene. This work provides the first molecular evidence
for ethylene response in fungi.
89 - Alteration of plant-pathogen interaction by
phytohormones
M. Al-Masri 1 , A. Sharon 2 & R. Barakat 1*
1
Hebron University, College of Agriculture, PO Box 40,
2
Hebron, Palestinian Authority, Israel. - Tel Aviv
University, Dept. of Plant Sciences, Tel Aviv 69978, Israel.
- E-mail: rbarakat@netvision.net.il
The effect of plant growth regulators on in vitro growth of
the pathogenic fungus Sclerotinia sclerotiorum and on
white mold disease that is caused by the pathogen was
investigated. Naphthalene acetic acid at concentrations of
200-400 µg/ml inhibited the fungal growth in culture and
reduced white mold severity on bean and cucumber plants.
Gibberellic acid at concentrations of 50-250 µg/ml
promoted both mycelium growth and white mold disease
severity on plants. Methyl jasmonate at concentrations of
75-250 µg/ml inhibited mycelium growth in culture and
suppressed bean and cucumber white mold. Absiscic acid
at concentrations of 100-300 µg/ml decreased mycelium
growth but promoted disease development on bean and
cucumber plants. Ethylene released from ethephon (200-
600 µg/ml) increased bean and cucumber white mold
severity. S. sclerotiorum has the capacity to produce
ethylene in culture. Ethylene production by S. sclerotiorum
reached peak (400 µl/g/h) after 6 days of incubation
followed by a decline to 155 µl/g/h after 10 days. The
ethylene biosynthesis inhibitor aminoethoxvinyleglycine
(AVG) suppressed white mold severity on bean and
cucumber plants at concentrations up to 300 µg/ml. The
results demonstrate a variable effect of plant hormones on
the development of white mold. The changes in disease
development may be due to both the effect of the plant
hormones on the susceptibility of the plant to infection as
well as due to a direct effect on the fungus.
90 - Differential effect of auxin-compounds produced by
two Pythium species with different pathogenicity
G. Le Floch 1* , P. Rey 1 , M.I. Salerno 2 , N. Benhamou 3 & Y.
Tirilly 1
1 Laboratoire de Microbiologie et Sécurité Alimentaire,
ESMISAB technopôle Brest Iroise 29 280 Plouzane,
France. - 2 Laboratorio de Proteccion Forestral, CISAUA-
Facultad de Ciencias Agrarias y Forestales UNLP 60 y
119 CC31 (1900) La Plata, Argentina. - 3 Département
Recherche en Sciences de la Vie et de la Santé, Pav. Ch.E.
Marchand, Université Laval Sainte-Foy Québec GIK7P4,
Canada. - E-mail: gaetan.lefloch@univ-brest.fr
Pythium ability to produce phytohormones-like compounds
has been frequently assumed to be involved in plant
Pythium relationship. This study shows that within Pythium
genus, two fungi: P. oligandrum and Pythium group F,
exert different effects on plant growth; both of them
produce auxin compounds through the tryptamine pathway
under the same cultural conditions. Indeed, the ability of
Pythium group F to produce indole-3-acetic acid (IAA) in
the immediate vicinity of roots had no positive effect on
plant development. On the contrary, P. oligandrum
production of tryptamine (TNH 2) was associated with
increased plant growth. Although analysis revealed marked
differences in auxin-compounds produced by both Pythium
in the plant nutrient solution, their differential influence on
tomato growth likely results from different fungal-plant
relationships. Pythium group F is a minor pathogen: it
causes symptomless infections, and then yield losses in
tomato soilless cultures; its hydrolytic enzymes, have a
destructive, though limited, impact on the root cell-walls of
the outer cortical area. So, one may hypothesise that the
effect of auxins on already damaged tissues dramatically
disturbs the host physiology. As a consequence, abnormal
root swellings and irregular plant development was
Book of Abstracts 29