Full text of DOI:10.1046/j.1439-0329.2000.00208.x

For. Path. 30 (2000) 247^263
#2000 Blackwell Wissenschafts-Verlag, Berlin
ISSN 1437 ^ 4781
Pathogenicity of fungi isolated from Quercus suberin Catalonia
(NE Spain)
¨
BY J. LUQUE, J. PARLADE and J. PERA
¨ ©
Dep. Proteccio Vegetal, Institut de Recerca i Tecnologia Agroalimentaries (IRTA), Centre de
Cabrils, Ctra. de Cabrils s.n., E-08348 Cabrils, Barcelona, Spain; E-mail: jordi.luque@irta.es
Summary
Thirty-four fungal species isolated from cork oak (Quercus suber) in Catalonia (NE Spain) during
1992^95 were tested for pathogenicity either in stem, leaf or root inoculations. Eleven species were
found to be pathogenic on stem: Biscogniauxia mediterranea, Botryosphaeria stevensii, Diatrype cf.
stigma, Endothia gyrosa, Fusarium solani, Graphium sp., Ophiostoma quercus, Phomopsis sp., Phy-
tophthora cinnamomi, Sporendocladia bactrospora and an unidenti¢ed Coelomycete. Three fungi
showed pathogenic e¡ects on leaves: Dendrophoma myriadea, Lembosia quercina and Phomopsis quer-
cella. No clear pathogenic e¡ects were detected in the root inoculation experiment. Trunk pathogens
were di¡erentiated into two groups according to the e¡ects induced in the inoculated plants; B. ste-
vensii, Phomopsis sp. and P. cinnamomi caused the death of the inoculated plants and induced the for-
mation of large cankers and vascular necroses. The other pathogenic species also produced severe
cankers and vascular lesions, but no signi¢cant mortality was detected. Water stress increased the
lesions caused by B. mediterranea and Phomopsis sp., but limited those of P. cinnamomi and the rest of
the inoculated fungi. However, water stress did not signi¢cantly a¡ect the damage caused byB. steven-
sii, which was the most virulent of the species tested. Leaf pathogens only showed their e¡ects if the
leaf cuticle was previously damaged. Lembosia quercina caused small dark lesions whereas D. myria-
dea and P. quercella produced large necrotic areas in well-watered plants. The lesions caused by the
last two fungi were reduced by water stress.
1 Introduction
In the last four decades a decline-type disease of cork oak (Quercus suber L.) has spread
through several regions of Spain. Preliminary studies associated the mortality of trees with
the following pathogenic fungi: Biscogniauxia mediterranea (de Not.) Kuntze (ˆ Hypoxy-
lon mediterraneum [de Not.] Ces. and de Not.) (OLIVA and MOLINAS 1984; TORRES JUAN
1985), Botryosphaeria stevensii Shoem. (anamorph: Diplodia mutila Fr. apud Mont.)
¬
(LUQUE and GIRBAL 1989; MUNOZ et al. 1992) and Phytophthora spp. (MOLINAS and OLIVA
1984; BRASIER et al. 1993). Moreover, additional research has focused on abiotic factors
such as climatic conditions (MONTOYA 1995) and other local site characteristics (JACOBS
et al. 1993).
In an exhaustive revision, FRANCESCHINI et al. (1993) compiled a list of about 300 fungal
species occurring on cork oak. This work reported about 100 pathogenic species, although
most of them were considered by the authors as secondary or weakness pathogens. Later,
MARRAS et al. (1995) established 16 taxa as the most relevant pathogen species in Sardinia
(Italy). Nevertheless, it is widely accepted that Armillaria mellea (Vahl: Fr.) Kumm., B.
mediterranea, B. stevensii and P. cinnamomi are the four main pathogens of cork oak in the
Mediterranean region (FRANCESCHINI et al. 1993; SANTOS 1995; BAKRY and ABOUROUH
¬
1996; MUNOZ et al. 1996; ROBIN et al. 1998). In addition, other locally abundant pathogens
Received: 18.1.2000; accepted: 27.4.2000; editor: T. Kowalski
U. S. Copyright Clearance Center Code Statement: 1437 ^ 4781/2000/3004 ^ 0247 $15.00/0

248
J. Luque, J. Parlade and J. Pera
may also be considered; for example, Endothia gyrosa (Schwein.: Fr.) Fr. (SANTOS 1995)
and several leaf fungi (MARRAS 1962a; MARRAS 1963).
The purpose of this research was to evaluate the pathogenicity of fungal species isolated
from cork oak in Catalonia during 1992^95. In order to assess the pathogenicity of the
fungi in relation to the hydric status of the host plant, inoculations on stem, leaf and root
were performed on plants subjected to two water treatments: adequate irrigation and
water stress.
2 Material and methods
2.1 Plant material and fungal strains
One-year-old cork oak seedlings obtained from ¢eld-collected acorns were used in all
pathogenicity tests. Acorns were sown in 1000 ml containers ¢lled with a peat^vermiculite
mixture (peat: Floratorf; Floragard, Oldenburg, Germany; vermiculite: Termita 2; Asfal-
tex, Valldoreix, Barcelona, Spain) in a 1 : 1 ratio (v/v). The substrate was amended with
Osmocote Plus1 (Grace-Sierra Spain, Tarragona, Spain) at a dose of 2.5 g/l (¢nal pH 5.0).
The plants were maintained in a greenhouse and irrigated twice a week to ¢eld capacity
until the setting up of the assays. Air temperature inside the greenhouse ranged from 15 to
42ꢀC during the experiments, and averaged 7ꢀC higher than the outside temperature. At
the time of inoculations the mean plant size was 30 cm tall with a 5 mm stem diameter mea-
sured 10 cm above the substrate level. Table 1 shows the 38 fungal strains used in the patho-
genicity tests, grouped by inoculation experiment: stem (32), leaf (four) and root (six). The
strains used in the experiments were obtained from cork oak trees surveyed in the regions
of Barcelona and Girona between 1992 and 1995 (LUQUE 1997). Fusarium solani (Mart.)
Sacc. and Verticillium tenerum (Nees ex Pers.) Link, although isolated from trunk, were
also tested in root inoculations. Similarly, the pathogenicity of P. cinnamomi was evaluated
by means of root and stem inoculations. All strains were maintained in potato-dextrose
agar (PDA) plugs in tubes with sterile distilled water at 4ꢀC before use, except for P. cinna-
momi, which was maintained in corn meal agar slants at 15ꢀC (both culture media from
Difco Laboratories, Detroit, MI, USA). Before the inoculations, the strains were recovered
by plating a mycelial plug in PDA and incubating it at 25ꢀC for 7 days.
2.2 Water stress
Plants used in stem and leaf experiments were distributed in two groups, one submitted
to water stress and the other to su¤cient water supply. Hydric stress was initiated about
50 days before the inoculations using two additional groups of 180 noninoculated plants
(90 stressed ‡90 irrigated). Leaf water potential (Cl) of each group was monitored once a
week (twice in summer months) at 0830 h (local time). Water potential was measured in
two leaves of ¢ve randomly selected plants using a pressure pump (Soil Moisture Equip-
ment, Santa Barbara, CA, USA), following the methods of SCHOLANDER et al. (1965).
The amount of water supplied to stressed plants, both inoculated and noninoculated,
was determined speci¢cally for each measurement time, and with the objective of main-
taining Cl below 1.4 MPa, a value which indicates water stress in evergreen Quercus (OLI-
VEIRA et al. 1992; TERRADAS and SAVE 1992). In order to prevent the death of stressed
seedlings, plants were rehydrated when mean Cl values were lower than 2.2 MPa. Non-
stressed plants were irrigated twice a week to ¢eld capacity to ensure appropriate water
availability.

Pathogenic fungi of cork oak
2.3 Pathogenicity tests
2.3.1 Stem inoculations
249
Plants of both irrigation treatments were inoculated in groups of 10 with a total of 32 fungal
strains (Table 1), in a completely randomized experimental design. A super¢cial wound
(15 mm  4 mm) was made on the bark of each plant at 10 cm above the ground level. A
mycelial plug (4 mm in diameter) obtained from the margin of a fungal colony was placed
in the wound, with the mycelium facing the stem, and the wound was wrapped with Paraf-
ilm1 (American National Can, Greenwich, CT, USA). Ten additional control plants were
treated similarly with sterile PDA plugs.
2.3.2 Leaf inoculations
A completely randomized experimental design was set up in which seedlings were inocu-
lated in groups of 10 plants with the four strains listed in Table 1. Three apparently healthy
leaves from the top of each plant were selected. The upper leaf surface was cleaned with
sterile distilled water and the cuticle was damaged with a needle (approximately 9 mm2) in
two out of the three leaves. The third nonwounded leaf was used to determine whether
infections could develop without previous damage. A mycelial plug (4 mm in diameter)
from the margin of a fungal colony was then placed on each leaf, covered with several pieces
of sterile ¢lter paper soaked with sterile distilled water and ¢nally wrapped with Para¢lm.
Paper pieces and Para¢lm were removed 2 weeks later and each leaf was appropriately
marked for future identi¢cation. Ten additional control plants were inoculated with sterile
PDA plugs using the same procedure.
2.3.3 Root inoculations
Root inoculations were performed only on plants with no water restrictions. Two weeks
before the inoculations, plants were transplanted to a steam-sterilized peat^vermiculite
substrate (1 h at 120ꢀC). Inoculations were made in groups of 10 plants with the six selected
strains in a completely randomized design (see Table 1). The inocula consisted of mycelial
homogenates (DHINGRA and SINCLAIR 1985); two fungal colonies of each strain previously
grown on solid media were blended in 120 ml of sterile distilled water for 10 s. Viability of
the fungi was assessed by plating 1 ml of the homogenates in PDA and checking for further
growth. Roots were damaged with a sterile blade, and 10 ml of the homogenates were
applied directly to the roots. An additional control group of 10 plants was established by
inoculating them with sterile media homogenates. Plants were maintained with subse-
quent periods of £ooding (two per week) throughout the experimental period.
2.4. Monitoring and data analysis
Each pathogenicity test was run for 6 months, between August 1994 and February 1996.
Symptom observations were made fortnightly and included foliar necroses, wilting or yel-
lowing, stem canker, epicormic branching, and production of fungal fruiting bodies. Three
months after the inoculations, half of the plants of each treatment were removed from the
assays. Symptoms were annotated once again and plants were processed in the following
ways:
Stem inoculations. The lengths of vascular necroses were measured upwards and down-
wards from the point of inoculation, and total necrosis was calculated. Fungal re-isolations
were accomplished by plating in PDA several surface-sterilized wood pieces (3 min in 70ꢀ
ethanol) taken from the necrotic tissues at intervals of 1 cm. Cultures were incubated at
25ꢀC for further identi¢cation of the isolated fungi.

250
J. Luque, J. Parlade and J. Pera

Pathogenic fungi of cork oak
251

252
J. Luque, J. Parlade and J. Pera
Leaf inoculations. Leaf necrotic area was estimated from the maximum and minimum
necrosis diameter. Fungal re-isolations were carried out as indicated above, but with sur-
face sterilization of leaf fragments limited to 20^30 s.
Root inoculations. Soil samples (approximately 250 ml) of the containers were baited with
immature carnation petals to recover the inoculated fungi. The root system of each plant
was carefully washed with tap water and the roots were later examined under a dissecting
microscope. Root fragments showing abnormal symptoms (colour, turgor, etc.) were
selected from each plant. Fragments were surface sterilized (0.5^2 min in 70ꢀ ethanol) and
plated in CMA, acidi¢ed PDA and PARP (KANNWISCHER and MITCHELL 1978). Cultures
were incubated at 25ꢀC for further identi¢cation of the tested fungi.
At the end of the experiments, all the above actions were repeated. Data from the assays
were analysed using SAS statistical package (SAS 1987). Data were checked for normality
and equal variance distributions, transformed if necessary, and analysed using multifactor-
ial analysis of variance (ANOVA) procedures. Data were grouped and analysed again if no
interactions were found. After ANOVA, mean treatment values were compared against their
respective controls with the Dunnett two-tailed test.
3 Results
3.1 Stem inoculations
Control plants from both irrigation treatments grew adequately and produced asympto-
matic leaves during all trials, although growth of stressed seedlings was lower in compari-
son with the su¤ciently irrigated plants. Regardless of water-supply level, wounds of all
control plants were covered by calli within the experimental period, and no fungus was iso-
lated from them. Table 2 summarizes the quantitative results obtained in the stem-inocula-
tion experiment. Statistical analyses were made separately for each irrigation treatment
and reading period due to signi¢cant interactions (p R0.05) between all factors (data not
shown). According to the results obtained, Botryosphaeria stevensii, Phytophthora cinna-
momi and Phomopsis sp. were highly virulent. All three fungi caused the death of inoculated
plants, large number of cankers, long vascular necroses, and were frequently re-isolated.
Botryosphaeria stevensii caused the death of nearly all plants in 7^14 days after the inocu-
lations. Wilting of seedlings coincided with the production of dark, depressed cankers, and
pycnidia on the bark surface. All plants were processed for symptom reading and pathogen
re-isolation in order to avoid secondary fungal colonizations. Mean vascular necroses were
the largest of all the inoculation treatments (21.0 and 18.0 cm for the normal irrigation and
stress assay, respectively). The dimensions of these lesions were equivalent to 60% of mean
plant height. Fungal colonization was, on average, about 2 cm larger than the necrosis.
Water stress did not a¡ect the lesions caused by B. stevensii, as shown by similar results
obtained in both assays.
About half of the seedlings inoculated with P. cinnamomi died within 1 month after the
inoculations regardless of the irrigation treatment. Cankers appeared in 19 plants and were
characterized by a depressed and very dark-coloured bark. Vascular necrosis in dead plants
monitored 3 months after inoculation was greater than that in surviving plants, which
explains the di¡erences observed in necrosis lengths between the two reading periods (see
Table 2). Water stress signi¢cantly decreased mean necrosis length (about 80%), as well as
the frequency of fungal recovery. Fungal colonization was strictly limited to the necrotic
zones.
Phomopsis sp. caused the death of all the inoculated plants submitted to water stress.
All inoculated plants regardless of the irrigation treatment developed bark cankers,
although cankers were externally less apparent in water-stressed plants. Vascular lesions at

Pathogenic fungi of cork oak
253
the end of the experiments were about 4 cm, slightly larger among stressed than non-
stressed plants. Mycelium re-isolation was positive in nearly all inoculated plants of both
irrigation treatments.
Only two plants inoculated with Biscogniauxia mediterranea and submitted to water
stress died during the experimental period. Cankers were not externally apparent although
vascular necroses were notable, especially in the water-stressed plants. Thus, the mean
values at the end of the experiments were 2.8 cm for the normal irrigation assay and 5.4 cm
for the water-stress experiment. Mycelial colonization was more extensive in stressed
plants, and averaged 1.5 cm larger than the necrosis length.
Diatrype cf. stigma (Ho¡m.: Fr.) Fr., Endothia gyrosa (Schwein.: Fr.) Fr., Fusarium solani
(Mart.) Sacc., Graphium sp., Ophiostoma quercus (Georgew.) Nannf., Sporendocladia bac-
trospora (Kendrick) M. Wing¢eld and the unidenti¢ed Coelomycete (no. 183) caused
numerous cankers, signi¢cant vascular necroses and were re-isolated very frequently. In
general, they did not lead to the death of inoculated plants and their lesions were reduced
under water-stress conditions (see Table 2 for exceptions). The three strains of F. solani
used in the experiments behaved di¡erently: strains 91 and 138 caused more cankers and
longer necroses than strain 143, whereas water stress decreased signi¢cantly the vascular
lesions of strains 138 and 143.
In comparison with the above fungi, the remaining inoculated strains produced rela-
tively minor lesions. In general, plants did not die and showed small bark cankers (limited
to 1^2 mm around the point of inoculation, with the exception of well-developed cankers
due to Coryneum quercinum Muthumary and Sutton, Pyrenochaeta quercina Kabat and
Bubak [no. 93] and Phomopsis quercella [Sacc. and Roum.] Died.). Mean vascular lesions
were normally nonsigni¢cant and shorter than 1 cm (except for Pestalotiopsis cf. guepinii
[Desm.] Stey., P. quercella and the unidenti¢ed Ascomycete [no. 168]; see Table 2). Mycelial
re-isolations were irregular, ranging from clearly positive (Petriella guttulata Barron and
Cain and Verticillium tenerum) to absolutely negative (Armillaria sp., Brachydesmiella
biseptata Arnaud ex Hughes and Splanchnonema sp.). There was also some variability in
the response of these fungi to water stress: in general, water stress decreased development
of canker and vascular necrosis as well as mycelial recovery. A clear increase in canker fre-
quencies was noticed only in the plants inoculated with the unidenti¢ed Ascomycete (no.
168), but slight increases were also found in plants inoculated with Armillaria sp., P. quer-
cina, Thyridaria macrostomoides (de Not.) Barr and V. tenerum.
3.2 Leaf inoculations
Foliar lesions caused by the inoculated fungi did not extend to other parts of the plant dur-
ing the experiment. They usually consisted of circular, necrotic, brown-coloured areas.
Table 3 summarizes the results obtained in this experiment. Analysis of variance showed a
signi¢cant interaction of all factors (p R0.5) except for the reading period (data not
shown).
In the normal irrigation assay, Dendrophoma myriadea (Preuss) Sacc. was the only fun-
gus that caused lesions in three out of 10 nonwounded leaves, although they were not statis-
tically signi¢cant. In addition, mycelial recovery from nonwounded leaves was possible
only for this fungus and B. mediterranea. On the other hand, only D. myriadea and Phomop-
sis quercella showed clear pathogenic e¡ects on wounded leaves, as indicated by large
necrotic areas (50 and 56 mm 2, respectively) and high percentages of mycelium recovery
(95 and 70%, respectively). Necroses caused by D. myriadea were detected in 95% of the
inoculated leaves and appeared 2 weeks after the inoculations. Those of P. quercella were
noticed 4^8 weeks after the inoculations and developed on 80% of the leaves. The other
fungi did not cause signi¢cant necroses although B. mediterranea was re-isolated from 50%
of the wounded leaves.

254
J. Luque, J. Parlade and J. Pera

Pathogenic fungi of cork oak
255

256
J. Luque, J. Parlade and J. Pera

Pathogenic fungi of cork oak
257
In the water-stress assay, only D. myriadea was re-isolated from nonwounded leaves,
but developed very small and nonsigni¢cant necroses. On damaged leaves, P. quercella
caused signi¢cant necroses and the percentage of mycelial recovery was over 50%. Dendro-
phoma myriadea and B. mediterranea were re-isolated in higher frequencies but no signi¢-
cant necroses were detected.
Lembosia quercina (Ell. and G. Martin) Tracy and Earle caused distinct lesions on the
upper surface of leaves: small black spots, with a regular and de¢ned margin (see MARRAS
1963). This fungus a¡ected plants of both irrigation treatments, but only on wounded
leaves. Mycelial recovery was not possible, probably due to an excessive sterilization of the
leaf fragments during re-isolation.
3.3 Root inoculations
Mycelial homogenation did not a¡ect fungal viability as shown by the positive colonial
recovery of all homogenates (Table 4). Only one plant inoculated with P. cinnamomi died
during the experimental period, and the rest of the inoculated plants behaved normally
throughout the assay (i.e. grew and produced green and asymptomatic leaves). Fusarium
oxysporum Schlecht., F. solani, P. cinnamomi and Pythium sp. were successfully recovered
using the soil-baiting technique, but only the three former species were re-isolated from
necrotic zones of the main and lateral roots; P. cinnamomi was re-isolated from eight plants,
F. solani from nine, and F. oxysporum from all the inoculated plants. Necrotic areas of the
main root, irrespective of the fungus inoculated, were sparse and measured only a few milli-
metres in size.
4 Discussion
Leaf water potential values of nonstressed plants, ranging from 0.7 to 0.3 MPa (mean:
0.4 MPa; SE 0.01 MPa), remained very stable during the entire experimental period.
These values corresponded to well-watered plants and coincided with similar measure-
ments made in natural conditions on nonstressed cork oak trees (OLIVEIRA et al. 1992). On
the other hand, Cl of stressed seedlings ranged from 3.0 to 0.4 MPa (mean: 1.3 MPa;
SE 0.03 MPa), showing a £uctuating pattern. KSONTINI et al. (1998) observed a reduction of
50% in stomatal conductance of young Quercus suber plants when water potential was
about 1.3 MPa, and a decrease of 70% at 1.7 MPa. On the other hand, TERRADAS and
SAVE (1992) found that adult trees of Quercus ilex L., another Mediterranean evergreen
Table 4. Number of plants showing infection symptoms and frequency of mycelial recovery of
Quercus suberseedlings (n = 10) inoculated with six species of root fungi
Number of plants
Inoculum
viability
Taxa
Dead
With main root
necrosis
Mycelium recovery
from soil baiting
Mycelium recovery
from roots
Control
^
0
0
0
1
0
0
0
0
10
10
10
2
0
10
10
10
2
10
0
0
10
9
Fusarium oxysporum
Fusarium solani
Phytophthora cinnamomi
Pythium sp. 1
‡
‡
‡
‡
‡
‡
8
0
Pythium sp. 2
Verticillium tenerum
3
0
0
0

258
J. Luque, J. Parlade and J. Pera
oak, progressively closed their stomata when water potential values were lower than
1.3 MPa, and trees su¡ered from severe water stress below 2.2 MPa. As a conclusion,
water restriction induced in Q. suber seedlings a moderate hydric stress punctuated by
more drastic episodes, as indicated by the lowest readings registered during this study
( 2.5 to 3.0 MPa). In relation to the development of the pathogenesis, water potential
between 1.2 and 1.5 MPa predisposes the host to most fungal infections of weakness
pathogens (SCHOENEWEISS 1978).
The results obtained in the stem-inoculation experiment show that Botryosphaeria ste-
vensii, Phomopsis sp. and Phytophthora cinnamomi were the most virulent pathogens. They
induced plant death and caused important canker and vascular lesions. Botryosphaeria ste-
vensii was the most signi¢cant virulent pathogen: it wilted seedlings in 7^14 days after
inoculations and showed the highest vascular colonization. LUQUE and GIRBAL (1989)
reported the pathogenicity of B. stevensii to cork oak, but in nonstressed plants. Our pre-
sent results indicate that B. stevensii maintains the same high level of virulence when the
host is under water stress. LUISI et al. (1993) observed similar results, also irrespective of
the water supply, in the inoculation of three Quercus species (Q. cerris L., Q. pubescens
Willd. and Q. trojana Webb.) with B. stevensii. This fungus is known to be pathogenic to the
following European species of Quercus in addition to cork oak: Q. cerris, Q. ilex, Q. petraea
(Matt.) Liebl., Q. pubescens, Q. robur L. and Q. trojana (ROLAND 1945; VAJNA 1986; RAGAZZI
and MESTURINO 1987; RAGAZZI et al. 1990; MUNOZ et al. 1992; LUISI et al. 1993).
Phytophthora cinnamomi caused the death of about half of the inoculated plants regard-
less of the irrigation treatment, although the vascular necroses and the mycelial recovery
were notably decreased when seedlings were subjected to water stress. ZENTMYER (1980)
pointed out that the optimal water potential for the in vitro growth of this species occurs at
the range of 1.0 to 1.5 MPa, whereas growth is reduced to a half when water potential is
between 2.0 and 2.5 MPa. Maybe the lowest potentials registered during our experi-
ment (approximately 3.0 MPa) negatively a¡ected the growth and viability of this fungus,
as shown by its low recovery frequency in the water-stress assay. Phytophthora cinnamomi
is a well known pathogen of more than 900 plant species, including cork oak and other spe-
cies of Quercus (MIRCETICH et al. 1977; ZENTMYER 1980). BRASIER et al. (1993), and recently
GALLEGO et al. (1999), identi¢ed P. cinnamomi as an important contributory factor in the
`oak decline' of Q. ilex and Q. suber woodlands in SW Spain. ROBIN et al. (1998) also recog-
nized the important role of P. cinnamomi in the decline after a survey for this pathogen in
cork and holm oak forests in south-east France.
Phomopsis sp. was especially virulent in the water-stress assay, causing the death of all
inoculated plants. However, canker production and vascular necroses were similar either
in normally irrigated or in stressed plants. Several species of Phomopsis are considered as
primary colonizers of twigs and are related with the natural pruning of trees (GRIFFITH and
BODDY 1990; KOWALSKI and KEHR 1992; HALMSCHLAGER et al. 1993; KEHR and WULF 1993;
SIEBER et al. 1995). Furthermore, some authors consider Phomopsis as moderately patho-
genic, and associated with Quercus dieback and decline (KOWALSKI 1991; KEHR and WULF
1993; SIEBER et al. 1995). On the other hand, the results of the present work showed a mod-
erate pathogenic behaviour of P. quercella in the trunk, thus coinciding with the opinion of
MARRAS et al. (1995) and MUNOZ et al. (1996).
Biscogniauxia mediterranea slightly increased the mortality of plants in the water stress
assay, although vascular lesions (over 5 cm) were approximately twice that observed in the
normal irrigation test. The pathogenic e¡ects of this species on several Mediterranean spe-
cies of Quercus are usually associated with stress episodes, such as summer drought
(TORRES JUAN 1985; CAPRETTI AND MUGNAI 1987; RAGAZZI et al. 1989; VANNINI and SCAR-
ASCIA MUGNOZZA 1991). The latter authors observed an optimal growth of this fungus
when xylem water potential of inoculated Q. cerris trees was at 2.0 MPa. VANNINI and
VALENTINI (1994), working with the same host^pathogen combination, found a positive

Pathogenic fungi of cork oak
259
relationship between stress conditions and the dimensions of the vascular necroses. Simi-
lar results were obtained by LUISI et al. (1993) with the inoculation of three Quercus species
with B. mediterranea. However, later studies have shown that B. mediterranea can also
induce negative e¡ects even in the absence of water stress: loss of xylem hydraulic conduc-
tivity, reduced stomatal conductance and low trunk diameter growth (VANNINI and
VALENTINI 1994; LUQUE et al. 1999).
Diatrype cf. stigma, Endothia gyrosa, Fusarium solani, Graphium sp., Ophiostoma quer-
cus, Sporendocladia bactrospora and the unidenti¢ed Coelomycete (no. 183) were moder-
ately virulent. They caused signi¢cant lesions but little seedling mortality. Water stress
increased lesions of D. cf. stigma and the unidenti¢ed Coelomycete (no. 183), whereas it
decreased those of S. bactrospora. To our knowledge, the speci¢c pathogenicity of these
fungi against Q. suber has not been proved yet, although some works consider the three for-
mer fungi as weak pathogens of cork oak (FRANCESCHINI et al. 1993; MUNOZ et al. 1996).
The rest of the strains tested for pathogenicity on stem did not show remarkable e¡ects.
However, some of them are known by their pathogenicity against Quercus, such as Armil-
laria and Ophiostoma. Armillaria spp. (mainly A. mellea and A. tabescens) are frequently
cited as cork oak pathogens (MARRAS 1962b; FRANCESCHINI et al. 1993; MARRAS et al. 1995;
MUNOZ et al. 1996). In our experiments, water stress slightly increased canker formation
by Armillaria sp., although the fungus was never re-isolated. Similarly, ANSELMI and PUCCI-
NELLI (1993) observed a signi¢cant increase in the lesions caused by A. mellea against six
Quercus species when plants were water stressed. Ophiostoma quercus (also known as a sib-
ling species within O. piceae [Munch] H. and P. Syd., see BRASIER 1993; BRASIER and KIRK
1993; BRASIER and STEPHENS 1993; HALMSCHLAGER et al. 1994; WULF and KOWALSKI 1994)
occurs on several species of Quercus. It has been frequently associated with the `oak
decline' complex, although its pathogenicity has been often discussed (mainly as O. piceae,
see DELATOUR 1983; OEPP/EPPO 1990; KOWALSKI 1991; BALDER 1993; DELATOUR et al.
1993). Our present results agree with those of BALDER (1993), who observed a reduction in
vascular necroses due to O. piceae when inoculated seedlings of Q. robur were submitted to
water stress.
Dendrophoma myriadea and Phomopsis quercella proved to be pathogenic to cork oak
in the leaf inoculation experiment. Both fungi caused lesions four to ¢ve times greater than
the control in the normal irrigation assay, but only if the leaf cuticle was damaged before
the inoculations. Water stress a¡ected both pathogens negatively, especially D. myriadea,
which produced nonsigni¢cant necroses. Dendrophoma myriadea is a known leaf pathogen
of Q. suber, which was ¢rst noticed on cork oak trees in Sardinian forests (MARRAS 1962a).
This fungus causes a characteristic marginal drying of leaves. However, MARRAS et al.
(1995) considered D. myriadea less virulent than other cork oak leaf pathogens, such as Elsi-
noe quercus-ilicis (Arn.) Jenkins and Goid. and Phloeospora ilicina Sacc. Phomopsis quercella,
which showed moderate pathogenic e¡ects in the stem assay, was clearly pathogenic on
leaf regardless of the irrigation treatment. This species was previously cited from cork oak
twigs (FRANCESCHINI et al. 1993; MUNOZ et al. 1996), but also from other Quercus, espe-
cially Q. robur and Q. petraea (DA CAMARA 1949; KOWALSKI and KEHR 1992; HALMSCHLAGER
et al. 1993; SIEBER et al. 1995). It has been previously reported that P. quercella developes an
endophytic growth inside the tree and takes advantage of stressed or dying tissues for
further colonization (GRIFFITH and BODDY 1990; KOWALSKI and KEHR 1992).
Biscogniauxia mediterranea did not cause any signi¢cant leaf lesions, but maintained
its viability regardless of the water treatment. Lembosia quercina must also be considered a
cork oak pathogen in spite of its negative re-isolation. Although foliar lesions caused by L.
quercina were scarce, small in size and re-isolations did not occur, there is no doubt that
inoculation produced the same characteristic symptoms as observed under natural condi-
tions. MARRAS (1963) noticed it on cork oak leaves for the ¢rst time in Sardinia. In addition
to Q. suber, 10 further host species of Quercus are cited for L. quercina (FARR et al. 1989).

260
J. Luque, J. Parlade and J. Pera
Although the pathogenicity of Fusarium, Phytophthora, Pythium and Verticillium spe-
cies is widely documented, none of the strains used in the root inoculation test showed
their pathogenicity clearly. Only F. oxysporum, F. solani and P. cinnamomi caused moderate
root lesions and, in general, there were no aerial symptoms except one plant killed by P. cin-
namomi. The reasons for failure of expression of pathogenicity are unknown but were
probably related to the experimental method. In spite of these negative results, stem inocu-
lations with F. solani and P. cinnamomi have shown the susceptibility of cork oak to these
species. On the other hand, V. tenerum, which also showed negative results in the root
inoculation experiment, was only moderately virulent when inoculated in the stems of
water-stressed plants.
In conclusion, 14 fungal species out of the 34 tested proved to be pathogenic; 11 on
stem and three on leaf. In addition to the widely known pathogens of cork oak such as B.
mediterranea, B. stevensii and P. cinnamomi, Phomopsis sp. was particularly virulent on
water-stressed plants. In general, trunk pathogens were a¡ected negatively by water stress,
as demonstrated by a reduction in both the number and size of the lesions. Nevertheless, B.
mediterranea and Phomopsis sp. increased the number of cankers and length of vascular
lesions under stress conditions, whereas B. stevensii did not seem to be a¡ected by water
restriction. The latter species was the most virulent of all the strains tested. Leaf pathogens
caused only local necroses and were in£uenced negatively by water stress.
Acknowledgements
J.L. was the recipient of a fellowship (FI-PG/94^9.806) provided by the Direccio General de Recerca
de la Generalitat de Catalunya, for the years 1994^97. The authors are grateful to the researchers who
kindly collaborated in fungal identi¢cations: Dr A. FRANCESCHINI and Professor F. MARRAS (Univer-
sita degli Studi, Sassari, Italy), Dr F. GENE and Dr J. GUARRO (Universitat Rovira i Virgili, Tarra-
gona, Spain), Dr J. DE GRUYTER (Plantenziektenkundige Dienst, Netherland), Professor T.
KOWALSKI (Akademia Rolnicza, Krakow, Poland), Dr M. C. MUNOZ and Dr C. SOLDEVILLA (Univer-
sidad Politecnica, Madrid, Spain), Dr H. NIRENBERG (Biologische Bundesanstalt fur Land und For-
stwirtschaft, Berlin, Germany), Professor B. C. SUTTON (Wenhaston, Su¡olk, UK). We also wish to
thank Dr C. ROCHE for the helpful comments made on a previous draft of this paper.
Resume
Pouvoir pathogene de champignons isoles de Quercus suber en Catalogne
Le pouvoir pathogene de trente-quatre especes fongiques isolees de chene liege en Catalogne (nord-
est de l'Espagne) de 1992 a 1995 a ete teste par inoculation sur tronc, feuilles et racines. Onze especes
se sont montrees pathogenes sur tronc: Biscogniauxia mediterranea, Botryosphaeria stevensii, Dia-
trype cf. stigma, Endothia gyrosa, Fusarium solani, Graphium sp., Ophiostoma quercus, Phomopsis sp.,
Phytophthora cinnamomi, Sporendocladia bactrospora et un Coelomycete non identi¢e. Trois cham-
pignons ont eu un e¡et pathogene sur feuilles: Dendrophoma myriadae, Lembosia quercina et Phomop-
sis quercella. Aucun e¡et clair n'a ete detecte chez les inoculations de racines. Les pathogenes de tronc
se repartissaient en deux groupes selon leurs e¡ets en inoculation; B. stevensii, Phomopsis sp. et P. cin-
namomi provoquaient la mort des plants et induisaient le formation de grands chancres et des
necroses vasculaires. Les autres especes pathogenes produisaient aussi des chancres graves et des
lesions vasculaires, mais pas de mortalite signi¢cative. Un stress hydrique augmentait les lesions pro-
voquees par B. mediterranea et Phomopsis sp. mais limitait ceux de P. cinnamomi et des autres cham-
pignons inocules. Cependant, le stress hydrique n'a¡ectait pas signi¢cativement les degats par B.
stevensii qui etait la plus agressive des especes testees. Les pathogenes foliaires n'avaient d'e¡et que si
la cuticule foliaire etait prealablement endommagee. Lembosia quercina provoquait de petites lesions
sombres et D. myriadea et P. quercella provoquaient de grandes plages necrotiques chez les plants
bien arroses; les lesions causees par ces deux derniers champignons etaient reduites par le stress
hydrique.

Pathogenic fungi of cork oak
261
Zusammenfassung
Pathogenitat von aus Quercus suber in Katalonien (Nordostspanien) isolierten Pilzen
Die Pathogenitat von 34 Pilzarten, die im Zeitraum 1992^1995 von Korkeichen (Quercus suber) in
Katalonien (NO-Spanien) isoliert wurden, wurden mit Hilfe von Trieb-, Blatt- oder Wurzelinokula-
tionen untersucht. Am Stamm erwiesen sich 11 Arten als pathogen: Biscogniauxia mediterranea,
Botryosphaeria stevensii, Diatrype cf. stigma, Endothia gyrosa, Fusarium solani, Graphium sp., Ophios-
toma quercus, Phomopsis sp., Phytophthora cinnamomi, Sporendocladia bactrospora und ein nicht
identi¢zierter Coelomycet. Drei Arten verursachten Symptome auf Blattern: Dendrophoma myria-
dea, Lembosia quercina und Phomopsis quercella. Bei den Wurzelinokulationen wurden keine patho-
genen E¡ekte beobachtet. Bei den Stammpathogenen wurden nach den von ihnen an den
inokulierten P£anzen verursachten Symptomen zwei Gruppen unterschieden: B. stevensii, Phomopsis
sp. und P. cinnamomi verursachten den Tod der P£anzen und induzierten die Bildung von grossen
Rinden- und Xylemnekrosen. Die anderen pathogenen Arten verursachten ebenfalls starke Rinden-
nekrosen und Gefasslasionen, es wurde jedoch keine au¡allende Mortalitat beobachtet. Unter Was-
serstress war die durch B. mediterranea und Phomopsis sp. induzierte Nekrosebildung verstarkt,
dagegen war sie bei P. cinnamomi und den ubrigen inokulierten Pilzen reduziert. Wasserstress beein-
£usst jedoch das Ausmass der Schadigung durch B. stevensii, der virulentesten der untersuchten
Arten, nicht. Die Blattpathogene verursachten nur dann Symptome, wenn zuvor die Blattcuticula
beschadigt worden war. Lembosia quercina verursachte kleine dunkle Lasionen, wahrend D. myria-
dea und P. quercella bei gut bewasserten P£anzen grosse Nekrosen verursachten. Diese Symptome
waren unter Wasserstress weniger stark ausgepragt.
References
ANSELMI, N.; PUCCINELLI, M., 1993: Studies on Armillaria attacks on declining oak trees. In: Proc.
Int. Cong. Recent Advances in Studies on Oak Decline. Selva di Fasano (Brindisi, Italy), Septem-
ber 13^18, 1992. Ed. by LUISI, N.; LERARIO, P.; VANNINI, A. Putignano (Italy): Tipolitogra¢a
Radio, pp. 23^29.
BAKRY, M.; ABOUROUH, M., 1996: Nouvelles donnees sur le deperissement du chene-liege (Quercus
suber L.) au Maroc. Ann. Rech. For. Maroc 29, 24^39.
BALDER, H., 1993: Pathogenicity of Ceratocystis spp. in oaks under stress. In: Proc. Int. Cong. Recent
Advances in Studies on Oak Decline. Selva di Fasano (Brindisi, Italy), September 13^18, 1992.
Ed. by LUISI, N.; LERARIO, P.; VANNINI, A. Putignano (Italy): Tipolitogra¢a Radio, pp. 31^37.
BRASIER, C. M., 1993: The genetic system as a fungal taxonomy tool: Gene £ow, molecular variation
and sibling species in the `Ophiostoma piceae ^ Ophiostoma ulmi' complex and its taxonomic and
ecological signi¢cance. In: Ceratocystis and Ophiostoma ^ Taxonomy, Ecology and Pathogeni-
city. Ed. by WINGFIELD, M. J.; SEIFERT, K. A.; WEBBER, J. F. St. Paul, MN, USA: APS Press, pp. 77^
92.
BRASIER, C. M.; KIRK, S. A., 1993: Sibling species within Ophiostoma piceae. Mycol. Res. 97, 811^
816.
BRASIER, C. M.; STEPHENS, T. M., 1993: Temperature-growth responses distinguish the OPC and
OPH sibling species within `Ophiostoma piceae'. Mycol. Res. 97, 1416^1418.
BRASIER, C. M.; ROBREDO, F.; FERRAZ, J. F. P., 1993: Evidence for Phytophthora cinnamomi involve-
ment in Iberian oak decline. Plant Pathol. 42, 140^145.
DA CAMARA, E. DA S., 1949: Mycetes aliquot Lusitaniae. IX. Agron Lusitana 11, 39^84.
CAPRETTI, P.; MUGNAI, L., 1987: Disseccamenti di cerro da Hypoxylon mediterraneum (de Not.)
Mill. Informatore Fitopatologico 37, 39^41.
DELATOUR, C., 1983: Les deperissements de chenes en Europe. Rev. For. Fr. 35, 265^282.
DELATOUR, C.; MENARD, J.; VAUTROT, A.; SIMONIN, G., 1993: Pathogenicity assessment of Ophiosto-
matales: Ophiostoma querci on oak compared to O. novo-ulmi on elm. In: Proc. Int. Cong. Recent
Advances in Studies on Oak Decline. Selva di Fasano (Brindisi, Italy), September 13^18, 1992.
Ed. by LUISI, N.; LERARIO, P.; VANNINI, A. Putignano (Italy): Tipolitogra¢a Radio, pp. 59^65.
DHINGRA, O. D.; SINCLAIR, J. B., 1985: Basic Plant Pathology Methods. Boca Raton, FL, USA: CRC
Press.
FARR, D. F.; BILLS, G. F.; CHAMURIS, G. P.; ROSSMAN, A. Y., 1989: Fungi on Plant and Plant Products
in the United States. St. Paul, MN, USA: APS Press.
FRANCESCHINI, A.; MARRAS, F.; SECHI, C., 1993: Funghi segnalati sulla quercia da sughero (Quercus
suber L.). Ed. by Stazione Sperimentale del Sughero (Tempio Pausania, Italy), Collana Biologica
3. Sassari (Italy): Stampacolor.

262
J. Luque, J. Parlade and J. Pera
GALLEGO, F. J.; DE ALGABA, A. P.; FERNANDEZ ESCOBAR, R., 1999: Etiology of oak decline in Spain.
Eur. J. For. Path. 29, 17^27.
GRIFFITH, G. S.; BODDY, L., 1990: Fungal decomposition of attached angiosperm twigs. I. Decay com-
munity development in ash, beech and oak. New Phytol. 116, 407^415.
HALMSCHLAGER, E.; BUTIN, H.; DONAUBAUER, E., 1993: Endophytische Pilze in Blattern und Zwei-
gen von Quercus petraea. Eur. J. For. Path. 23, 51^63.
HALMSCHLAGER, E.; MESSNER, R.; KOWALSKI, T.; PRILLINGER, H., 1994: Di¡erentiation of Ophios-
toma piceae and Ophiostoma quercus by morphology and RAPD analysis. System. Appl. Micro-
biol. 17, 554^562.
JACOBS, K. A.; ALVAREZ, I. F.; LUQUE, J., 1993: Association of soil, site and stand factors with decline
of Quercus suber in Catalonia, Spain. In: Proc. Int. Cong. Recent Advances in Studies on Oak
Decline. Selva di Fasano (Brindisi, Italy), September 13^18, 1992. Ed. by LUISI, N.; LERARIO, P.;
VANNINI, A. Putignano (Italy): Tipolitogra¢a Radio, pp. 193^203.
KANNWISCHER, M. I.; MITCHELL, D. J., 1978: The in£uence of a fungicide on the epidemiology of
black shank of tobacco. Phytopathology 68, 1760^1765.
KEHR, R. D.; WULF, A., 1993: Fungi associated with above-ground portions of declining oaks (Quercus
robur) in Germany. Eur. J. For. Path. 23, 18^27.
KOWALSKI, T., 1991: Oak decline: I. Fungi associated with various disease symptoms on overground
portions of middle-aged and old oak (Quercus robur L.). Eur. J. For. Path. 21, 136^151.
KOWALSKI, T.; KEHR, R. D., 1992: Endophytic fungal colonization of branch bases in several forest
tree species. Sydowia 44, 137^168.
KSONTINI, M.; LOUGUET, P.; LAFFRAY, D.; REJEB, M. N., 1998: Comparison of the water stress e¡ects
on stomatal conductance, photosynthesis and growth of Mediterranean oak seedlings (Quercus
suber, Q. faginea, Q. coccifera) in Tunisia. Ann. Sci. For. 55, 477^495.
LUISI, N.; MANICONE, R. P.; SICOLI, G.; LERARIO, P., 1993: Pathogenicity tests of fungi associated
with oak decline on Quercus spp. seedlings grown at di¡erent water regimes. In: Proc. Int. Cong.
Recent Advances in Studies on Oak Decline. Selva di Fasano (Brindisi, Italy), September 13^18,
1992. Ed. by LUISI, N.; LERARIO, P.; VANNINI, A. Putignano (Italy): Tipolitogra¢a Radio, pp. 85^
93.
LUQUE, J., 1997: Biologia i etiologia de fongs patogens de l'alzina surera a Catalunya. Ph.D. Thesis.
Bellaterra (Spain): Universitat Autonoma de Barcelona.
LUQUE, J.; COHEN, M.; SAVE, R.; BIEL, C.; ALVAREZ, I. F., 1999: E¡ects of three fungal pathogens on
water relations, chlorophyll £uorescence and growth of Quercus suber L. Ann. For. Sci. 56, 19^
26.
LUQUE, J.; GIRBAL, J., 1989: Dieback of cork oak (Quercus suber) in Catalonia (NE Spain) caused by
Botryosphaeria stevensii. Eur. J. For. Path. 19, 7^13.
MARRAS, F., 1962a: Contributi alla patologia della quercia da sughero (Quercus suber L.) II. Malattie
fogliari causate da funghi parasiti in Sardegna. Ed. by Stazione Sperimentale del Sughero (Tem-
pio Pausania, Italy), Memoria 3. Sassari (Italy): Gallizzi.
MARRAS, F., 1962b: Contributi alla patologia della quercia da sughero (Quercus suber L.) III. Il `mar-
ciume radicale' causato da Armillaria mellea (Vahl) Quel. Ed. by Stazione Sperimentale del
Sughero (Tempio Pausania, Italy), Memoria 4. Sassari (Italy): Gallizzi.
MARRAS, F., 1963: Contributi alla patologia della quercia da sughero (Quercus suber L.) IV. Ticchiola-
tura delle foglie Morenoella quercina (Ell. et Mart.) Theiss. Ed. by Stazione Sperimentale del
Sughero (Tempio Pausania, Italy), Memoria 7. Sassari (Italy): Gallizzi.
MARRAS, F.; FRANCESCHINI, A.; MADDAU, L., 1995: Les principales maladies du chene-liege (Quercus
suber L.) en Sardaigne (Italie). IOBC/WPRS Bull. 18, 8^13.
MIRCETICH, S. M.; CAMPBELL, R. N.; MATHERON, M. E., 1977: Phytophthora trunk canker of coast
live oak and cork oak trees in California. Plant Dis. Rep. 61, 66^70.
MOLINAS, M. L.; OLIVA, M., 1984: Aislamiento de Phytophthora de Bary de alcornoques afectados de
escaldado (1). Bolet|n Estacion Central Ecolog|a ICONA 13, 25^28.
MONTOYA, J. M., 1995: Efecto del cambio climatico sobre los ecosistemas forestales espanoles. Cua-
dernos Sociedad Espanola Ciencias Forestales 2, 65^76.
MUNOZ, M. C.; COBOS, P.; MARTINEZ, G., 1992: La traqueomicosis de Diplodia sp. sobre Quercus sp.
Bolet|n Sanidad Vegetal Plagas 18, 641^657.
MUNOZ, M. C.; COBOS, P.; MARTINEZ, G.; SOLDEVILLA, C.; DIAZ, M., 1996: Mico£ora y patolog|a del
alcornoque (Quercus suber L.). Ed. by Ministerio de Agricultura, Pesca y Alimentacion. Madrid
(Spain): MAPA.
OEPP/EPPO, 1990: Oak decline and the status of Ophiostoma spp. on oak in Europe. OEPP/EPPO
Bull. 20, 405^422.

Pathogenic fungi of cork oak
263
OLIVA, M.; MOLINAS, M. L., 1984: Incidencia de Hypoxylon mediterraneum en los alcornocales gerun-
denses. Bolet|n Estacion Central Ecolog|a ICONA 13, 9^16.
OLIVEIRA, G.; CORREIA, O.; MARTINS-LOU´AO, M. A.; CATARINO, F. M., 1992: Water relations of
cork-oak (Quercus suber L.) under natural conditions. Vegetatio 99^100, 199^208.
RAGAZZI, A.; DELLAVALLE, I.; MESTURINO, L., 1989: The oak decline: a new problem in Italy. Eur. J.
For. Path. 19, 105^110.
RAGAZZI, A.; DELLAVALLE, I.; MORICCA, S., 1990: Modello di colonizzazione di Quercus cerris da
parte di Diplodia mutila e Phomopsis quercina. Phytopathologia Med. 29, 209^212.
RAGAZZI, A.; MESTURINO, L., 1987: Diplodia mutila in Italia: associata al `deperimento della quercia'?
Italia Forale Montana 42, 264^274.
ROBIN, C.; DESPREZ-LOUSTAU, M. L.; CAPRON, G.; DELATOUR, C., 1998: First record of Phytophthora
cinnamomi on cork and holm oaks in France and evidence of pathogenicity. Ann. Sci. For. 55,
869^883.
ROLAND, G., 1945: Etude faite sur une tracheomycose du chene occasionnee par un Diplodia. Parasi-
tica 1, 11^36.
SANTOS, M. N. S., 1995: Phytopathological situation of cork oak (Quercus suber L.) in Portugal.
IOBC/WPRS Bull. 18, 38^42.
SAS, 1987: SAS/STAT1 Guide for Personal Computers, Version 6 Edition. Cary, NC, USA: SAS
Inc.
SCHOLANDER, P. F.; HAMMEL, H. T.; BRADSTREE, E. D.; HEMMINGSEN, E. A., 1965: Sap pressure in vas-
cular plants. Science 148, 339^346.
SCHOENEWEISS, D. F., 1978: Water stress as a predisposing factor in plant disease. In: Water De¢cits
and Plant Growth. Ed. by KOZLOWSKI, T. T. St. Paul, MN, USA: APS Press, pp. 61^99.
SIEBER, T. N.; KOWALSKI, T.; HOLDENRIEDER, O., 1995: Fungal assemblages in stem and twig lesions
of Quercus robur in Switzerland. Mycol. Res. 99, 534^538.
TERRADAS, J.; SAVE, R., 1992: The in£uence of summer and winter stress and water relationships on
the distribution of Quercus ilex L. Vegetatio 99^100, 137^145.
TORRES JUAN, J., 1985: El Hypoxylon mediterraneum (de Not.) Mill. y su comportamiento en los enci-
nares y alcornocales andaluces. Bolet|n Servicio Plagas 11, 185^191.
VAJNA, L., 1986: Branch canker and dieback of sessile oak (Quercus petraea) in Hungary caused by
Diplodia mutila. I. Identi¢cation of pathogen. Eur. J. For. Path. 16, 223^229.
VANNINI, A.; SCARASCIA MUGNOZZA, G., 1991: Water stress: a predisposing factor in the pathogenesis
of Hypoxylon mediterraneum on Quercus cerris. Eur. J. For. Path. 21, 193^201.
VANNINI, A.; VALENTINI, R., 1994: In£uence of water relations on Quercus cerris^Hypoxylon mediter-
raneum interaction: a model of drought-induced susceptibility to a weakness parasite. Tree Phy-
siol. 14, 129^139.
WULF, A.; KOWALSKI, T., 1994: Die Wachstumsgeschwindigkeit als Unterscheidungsmerkmal
zwischen Ophiostoma piceae und Ophiostoma querci. Eur. J. For. Path. 24, 123^127.
ZENTMYER, G. A., 1980: Phytophthora cinnamomi and the Diseases It Causes. Ed. by American Phyto-
pathological Society, Monograph, 10. St. Paul, MN, USA: APS Press.