In vitro growth of some species of Ascochyta Lib

Abstract

Fungi from the genus Ascochyta are generally facultative saprotrophs, which cause diseases in both monocots and dicots. Over 1 000 species belonging to this genus have been identified, 18 of which infect monocot plants from the family Poaceae. This study analyses the effects of temperature and light on the growth of selected fungi which infect monocots (A. agrostidis, A. avenae, A. brachypodii, A. desmazieri, A. digraphidis, A. ducis-aprutii, A. festucae, A. graminea, A. hordei, A. hordei var. americana, A. hordei var. europea, A. hordei var. hordei, A. melicae, A. phleina, A. skagwayensis, A. sorghi, A. stipae, A. zeicola), grown on three types of media; Potato Dextrose Agar (PDA), Coon’s agar (CN) and oatmeal agar (OMA). The fastest growth among the analyzed fungi at low temperatures was found in Ascochyta melicae, while at high temperatures it was A. zeicola. The fastest in vitro growth (average of all fungi) was observed on CN medium at 20°C (3.4 mm/day), while the lowest on OM medium at 5°C (1.0 mm/day). Radial mycelial growth in dark and the light conditions varied. On average, all isolates grew faster in the dark (3.1 mm/day) than in the light (1.9 mm/day). The greatest effect on the production of pycnidia was found for the isolates. Variation in growth and production of pycnidia depended on temperature, medium and lighting for fungi from the genus Ascochyta infecting monocots. Such variation indicates a potential occurrence of these fungi in different environments.

Full text

Central European Journal of Biology
* E-mail: kosiada@up.poznan.pl
Research Article
Poznań University of Life Sciences,
Department of Phytopathology,
60–594 Poznań, Poland
Tomasz Kosiada*
In vitro
growth of some species of
Ascochyta
Lib.
1. Introduction
Most species of fungi from the genus Ascochyta are
facultative saprotrophs. These organisms are known to
cause diseases in a variety of mono- and dicot plants.
In 1977, over 1 000 fungal species from the genus
Ascochyta were described worldwide, though a large
proportion of these species were later reclassied as
synonyms. To date, no comprehensive description
or classication of the species in this genus has
been developed. Ascochyta fungi infect plants of the
family Poaceae, with 18 plant species known to be
diseased by members of this genus [1,2]. In the case
of these host plants, the fungus is considered a “weak”
pathogen (they become activated when the functioning
of the immune system is disturbed or inhibited). Still,
the fungi from the genus Ascochyta have the potential
to infest commercially grown cereals, particularly wheat
and barley, and grasses [3-6]. Thus, it is important
to identify the environmental requirements of these
pathogens in order to provide better management
strategies for plant protection. Determining optimal
growth and sporulation conditions of these fungi may
facilitate the identication of conditions that may lead
to plant infestation.
2. Experimental Procedures
The experiments were conducted in vegetation
chambers at constant temperatures of 5, 10, 15, 20
or 25ºC. Additionally, the development of fungi was
investigated in chambers kept at a temperature of 20ºC
with a 12-h light cycle using Osram L36W/76 articial
light and Philips TLD 36W/108 uorescent lamps
(180 W/m2). Analyzed isolates of fungi from the genus
Cent. Eur. J. Biol. • 7(6) • 2012 • 1076-1083
DOI: 10.2478/s11535-012-0095-3
1076
Received 23 April 2012; Accepted 28 August 2012
Keywords: Growth of fungi • Monocotyledonous plant pathogen
Abstract: Fungi from the genus Ascochyta are generally facultative saprotrophs, which cause diseases in both monocots and dicots. Over
1 000 species belonging to this genus have been identied, 18 of which infect monocot plants from the family Poaceae. This study
analyses the effects of temperature and light on the growth of selected fungi which infect monocots (A. agrostidis, A. avenae,
A. brachypodii, A. desmazieri, A. digraphidis, A. ducis-aprutii, A. festucae, A. graminea, A. hordei, A. hordei var. americana,
A. hordei var. europea, A. hordei var. hordei, A. melicae, A. phleina, A. skagwayensis, A. sorghi, A. stipae, A. zeicola),
grown on three types of media; Potato Dextrose Agar (PDA), Coon’s agar (CN) and oatmeal agar (OMA). The fastest growth
among the analyzed fungi at low temperatures was found in Ascochyta melicae, while at high temperatures it was A. zeicola.
The fastest in vitro growth (average of all fungi) was observed on CN medium at 20ºC (3.4 mm/day), while the lowest on OM
medium at 5ºC (1.0 mm/day). Radial mycelial growth in dark and the light conditions varied. On average, all isolates grew
faster in the dark (3.1 mm/day) than in the light (1.9 mm/day). The greatest effect on the production of pycnidia was found for
the isolates. Variation in growth and production of pycnidia depended on temperature, medium and lighting for fungi from the
genus Ascochyta infecting monocots. Such variation indicates a potential occurrence of these fungi in different environments.
© Versita Sp. z o.o.

T. Kosiada
Ascochyta were obtained from the plant pathogen
collection at the Department of Phytopathology, the
Poznań University of Life Sciences, Poland and
Centraalbureau voor Schimmelcultures (CBS) Fungal
Biodiversity Centre. Fungi were isolated from cereal
and grass plants.
Polystyrene Petri dishes were covered with 5mm
discs of PDA media overgrown with the respective
fungal isolates. The 24-h radial growth increment was
calculated by subtracting ½ of the colony’s diameter at
day 2 from ½ of the colony’s diameter at day 7. Fungal
development was analyzed on a standard PDA (Potato
Dextrose Agar, Sigma P2182) medium, and on two
media recommended for the growth of pycnidia-forming
fungi, OMA (oatmeal agar Sigma-O3506) [7,8], and
CN (Coon’s agar) [9,10]. The optimal temperature was
determined by the fastest in vitro radial growth for the
same isolate grown on different media. Observations of
pycnidium production were taken in the course of the
mycelial growth measurements.
Statistical analyses were performed using the
software package Statistica version 8.0. Analyses of
variance (ANOVA) were conducted and homogeneous
groups were identied with the use of the Newman–
Keuls test. A two-way ANOVA was performed, with
temperature (T) and culture medium (M) as factors
(Table 2). Another two-way ANOVA was conducted
(Table 3), with fungal isolate (S) and light condition (L)
as factors.
Regression curves of fungal growth within the
range of temperatures from 5 to 25ºC (temperature
points at every 5 degrees), where f(T)=β0+β1T+β2T2
were plotted. Next, The maximum of each function
was calculated when Δ>0 (Δ=β1
2- 4·β2 · β0). There are
two results of the function expressed by the following
formulas:
T
1
=−β
1
−
√
Δ
2β
2
;
T
2
=−β
1
−
√
Δ
2β
2
,
when Δ=0, this is a one result expressed by the
formula:
T1=−β1
2β2
, where Δ<0,
where there are no results (Table 1). When the
resulting function did not have a maximum or the
maximum was found outside the analyzed temperature
range, the optimal growing temperature for the fungi was
not determined. A Principal Component Analysis (PCA)
was conducted and the location of points was presented
in a scatterplot representing growth of individual isolates
(Figures 1,2).
3. Results
The optimal temperature for fungal growth depended
on the culture medium (Table 1). The coefcient of
determination (R2) exceeded 0.5 in most cases. Optimal
temperature varied, although these differences were
smaller than the variation in growth found among
isolates. Differences were also found between optimal
growth temperatures within a species grown on different
media. The species A. avenae (isolate 1982), was
characterized by optimal growth temperatures ranging
from 18.2 to 21.9ºC, while another isolate (C811.84a)
had a much lower optimal temperatures of 14.6 to
15.3ºC. A slightly lower variation was observed within
A. brachypodii: from 15.8 to 16.2ºC, from 14.9 to 15.5ºC
and from 19.1 to 21.7ºC for isolates 1155, 1523a/2 and
1968a, respectively. The lowest optimal temperature
for fungal growth was 14.1 to 14.9ºC observed in
A. melicae (2010), while the highest was found for
A. zeicola at 24.2ºC. There was a signicant effect of
temperature, medium and the interaction between
temperature and medium on fungi growth (temperature
(T): df=4, F=1970.02, P=0.000, medium (M): df=2,
F=28.95, P=0.000, for interaction C*I: df=8, F=11.13,
P=0.000). The fastest growth of all the Ascochyta
fungi was recorded on Coon’s medium (CN), whereas
differences in growth between Potato Dextrose Agar
(PDA) and oatmeal agar (OMA) were non-signicant.
The average growth on OMA was 2.1 mm/day. There
were signicant differences in fungal growth among all
the analyzed temperatures, with radial growth slowing
down with decreasing temperature: 3.2 mm/day (20ºC),
2.9 mm/day (15ºC), 2.4 mm/day (25ºC), 1.3 mm/day
(10ºC) and 1.1 mm/day (5ºC). An interaction was found
between the analyzed factors, which makes it possible
to state the best temperature-medium combination. The
best temperature/medium combination for fungal growth
was 20ºC using Coon’s agar (3.4 mm/day), whereas
the worst combination was 5ºC and oatmeal agar
(1.0 mm/day) as well as Coon’s agar (1.1 mm/day).
When fungal growth was assessed on PDA medium in
different lighting scenarios, the growth rate of fungi in
the dark was markedly higher (3.1 mm/day) than the
growth rate under 12 h of light (1.9 mm/day, ANOVA for
strains (S): df=25, F=25.447, P=0.000, for light (L): df=1,
F=62.774, P=0.000, for interaction C*I: df=25, F=7.985,
P=0.000, Table 3).
Reaction of species and isolates to different light
conditions varied greatly. For A. brachypodii (1523a/2),
A. hordei var. europea (C817.84) and A. phleina
(C517.74), growth in the dark and in the light was very
similar. In turn, the following isolates responded with
considerably slower growth under light: A. brachypodii
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In vitro
growth of some species of
Ascochyta
Lib.
Figure 1. Distribution of points representing growth of fungi from the genus Ascochyta at different temperatures and on different media in the
system of two principal components.
A. agrostidis- C758.97 (Aag), A. avenae- 1982 (Aav), C811.84a (Aav), A. brachypodii- 1155 (Ab),1523a/2 (Ab), 1968a (Ab),
A. desmazieri- C247.79 (Ade), A. digraphidis- 1968b(Adi), A. ducis-aprutii- 1915(Ada), A. festucae- C689.97 (Af), A. graminea- C586.79
(Ag), A. hordei- 1684 (Ah), 1971 (Ah), 770b (Ah), A. hordei var. americana- C814.84 (Aha), A. hordei var. europea- C817.84 (Ahe),
A. hordei var. hordei- C878.72a (Ahh), A. melicae- 2010 (Am), 793c (Am), A. phleina- C517.74 (Ap), A. skagwayensis- C110124 (Ask),
A. sorghi- C622.68 (Aso), A. stipae- 1811 (Ast), A. zeicola- 1937 (Az)
Figure 2. Distribution of straights representing different media in the system of two principal components.
C758.97 (Aag)
1982 (Aav )C811.84a (Aav )
1155 (Ab) 1523a/2 (A b)
1968a (Ab)
C247.79 (Ade)
1968b(Adi)
1915(Ada)
C689.97 (Af )
C586.79 (Ag)
1684 (Ah)
1971 (Ah)
770b (Ah)
C814.84 (Aha)
C817.84 (Ahe)
C878.72a (Ahh)
2010 (Am)
793c (A m)
C517.74 (Ap)
C110124 (Ask)
C622.68 (Aso)
1811 (As t)
1937 (Az )
-4 -3 -2 -1 0 1 2 3 4 5 6
Component 1: 86,13%
-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
Component 2: 10,23%
C758.97 (Aag)
1982 (Aav )C811.84a (Aav )
1155 (Ab) 1523a/2 (A b)
1968a (Ab)
C247.79 (Ade)
1968b(Adi)
1915(Ada)
C689.97 (Af )
C586.79 (Ag)
1684 (Ah)
1971 (Ah)
770b (Ah)
C814.84 (Aha)
C817.84 (Ahe)
C878.72a (Ahh)
2010 (Am)
793c (A m)
C517.74 (Ap)
C110124 (Ask)
C622.68 (Aso)
1811 (As t)
1937 (Az )
CN
OMA
PDA
-1,0 -0,5 0,0 0,5 1,0
Component 1 : 86,13%
-1,0
-0,5
0,0
0,5
1,0
Component 2 : 10,23%
CN
OMA
PDA
1078

T. Kosiada
(1155), (1968a), A. digraphidis (1968b), A. ducis-aprutii
(1915) and A. hordei (1684), (1971), (770b). The fastest
growing fungi were A. agrostidis (C758.97), A. festucae
(C689.97), A. graminea (C586.79), A. hordei (1971),
A. hordei var. americana (C814.84), A. melicae (2010),
A. sorghi (C622.68) and A. zeicola (1937). They each grew
at a rate of more than 3.0 mm/day. The slowest growth
was recorded for A. phleina (C517.74), which grew at a
rate of 0.4 mm/day. Observations of pycnidium production
conducted at different temperatures, on different mediums
and at different lighting regimes show that a given fungal
isolate plays a decisive role in pycnidium formation or its
absence (Table 4). Fungi in which pycnidium generation
was observed included A. brachypodii (1523a/2),
A. hordei (1684), A. hordei var. europea (C817.84),
A. hordei var. hordei (C878.72a), A. skagwayensis
(C110124) and A. zeicola (1937). In these isolates, the
production of pycnidia was observed only under certain
growth conditions. Pycnidium formation was promoted by
alternating light conditions and culture on oatmeal agar.
A Principal Component Analysis was performed to obtain
homogeneous information. The many factors inuencing
the growth of Ascochyta were taken into consideration.
Interdependencies determining the growth of individual
isolates at different conditions are presented in Figure 1.
A close location of points representing individual isolates
reects a similar growth rate of these isolates at different
temperatures and on different media. The reaction of
isolates within A. hordei varied, as shown by the high
scatter of points representing these isolates. It is difcult
to isolate distinct groups on the graph, but considerable
separation from the other isolates can be observed in the
Species Isolate
Temperature [ºC] adjusted R2
CN OMA PDA CN OMA PDA
A. agrostidis C758.97 –* –* –* – – –
A. avenae 1982 20.7 21.9 18.2 0.87 0.77 0.61
A. avenae C811.84a 14.6 15.3 14.9 0.44 0.65 0.67
A. brachypodii 1155 16.2 15.8 16.0 0.70 0.84 0.72
A. brachypodii 1523a/2 15.4 14.9 15.5 0.58 0.60 0.50
A. brachypodii 1968a 21.7 19.1 20.2 0.79 0.85 0.67
A. desmazieri C247.79 –* –* –* – – –
A. digraphidis 1968b 20.1 16.0 16.2 0.5 0.69 0.62
A. ducis-aprutii 1915 15.3 15.2 14.9 0.6 0.68 0.64
A. festucae C689.97 –* –* –* – – –
A. graminea C586.79 23.2 19.5 18.8 0.79 0.68 0.42
A. hordei 1684 –* –* –* – – –
A. hordei 1971 16.9 16.1 17.1 0.61 0.64 0.78
A. hordei 770b –* –* 16.5 – – 0.24
A. hordei var. americana C814.84 19.3 16.6 22.7 0.72 0.74 0.71
A. hordei var. europea C817.84 –* –* –* – – –
A. hordei var. hordei C878.72a 20.8 18.4 –* 0.84 0.57 –
A. melicae 2010 14.5 14.9 14.1 0.72 0.68 0.49
A. melicae 793c 17.0 15.4 15.7 0.46 0.69 0.67
A. phleina C517.74 –* –* –* – – –
A. skagwayensis C110124 16.7 15.8 15.6 0.70 0.63 0.73
A. sorghi C622.68 23.1 18.1 20.8 0.85 0.81 0.74
A. stipae 1811 15.3 15.2 14.9 0.45 0.35 0.25
A. zeicola 1937 –* 24.2 –* – 0.80 –
Table 1. Optimal temperature for the fastest growth of Ascochyta spp. isolates and R2 for the model.
*optimal temperature for the fastest fungal growth lies outside the analyzed area, or the function has no maximum
CN - Coon’s agar; OMA - oatmeal agar; PDA - Potato Dextrose Agar
1079

In vitro
growth of some species of
Ascochyta
Lib.
Medium
Temperature [ºC]
5ºC 10ºC 15ºC 20ºC 25ºC Mean
CN 1.1 1.3 3.0 3.4 2.6 2.3
OMA 1.0 1.4 2.8 3.0 2.3 2.1
PDA 1.2 1.3 2.8 3.1 2.2 2.1
LSDN-K 0.05 0.12 0.13
Mean 1.1 1.3 2.9 3.2 2.4
LSDN-K 0.05 0.19
Table 2. Radial growth of Ascochyta spp. fungi on different media at different temperatures.
CN - Coon’s agar; OMA - oatmeal agar; PDA - Potato Dextrose Agar
Species Isolate
Fungal growth [mm/day]
Mean
in the dark 12 h darkness/12 h light
A. agrostidis C758.97 4.1 3.2 3.6
A. avenae 1982 3.1 1.6 2.4
A. avenae C811.84a 2.9 1.5 2.2
A. brachypodii 1155 4.3 0.9 2.6
A. brachypodii 1523a/2 1.1 1.1 1.1
A. brachypodii 1968a 3.5 1.4 2.5
A. desmazieri C247.79 2.4 1.7 2.0
A. digraphidis 1968b 3.7 1.4 2.5
A. ducis-aprutii 1915 3.1 0.4 1.8
A. festucae C689.97 4.4 2.4 3.4
A. graminea C586.79 3.6 3.3 3.4
A. hordei 1684 3.6 2.1 2.8
A. hordei 1971 4.1 2.0 3.1
A. hordei 770b 3.3 1.9 2.6
A. hordei var. americana C814.84 3.7 2.3 3.0
A. hordei var. europea C817.84 1.8 1.9 1.8
A. hordei var. hordei C878.72a 2.8 1.5 2.1
A. melicae 2010 3.9 2.1 3.0
A. melicae 793c 3.7 1.6 2.6
A. phleina C517.74 0.5 0.3 0.4
A. skagwayensis C110124 3.3 2.4 2.8
A. sorghi C622.68 3.6 2.4 3.0
A. stipae 1811 3.1 2.1 2.6
A. zeicola 1937 3.3 3.0 3.1
LSDN-K 0.05 0.06 0.11
mean 3.1 1.9
Table 3. Radial growth of Ascochyta spp. fungi on PDA medium at 20ºC in the dark and in the light (12 h light/12 h darkness).
1080

T. Kosiada
case of A. phleina - C517.74, which was characterized by
the slowest growth. The points illustrating A. brachypodii
- 1523a/2, A. hordei - 1684, A. agrostidis - C758.97,
A. festucae - C689.97 are also located at slight distances
from the other isolates. The presented graph reects a
considerable part of the total variation of the investigated
system, as it is as much as 96.33%.
A dependence between media in the system of
two principal components is presented in Figure 2.
The location of straight lines in relation to one another
shows a high positive correlation between fungal growth
on oatmeal agar (OMA) and Coon’s agar (CN). The
correlation between growth on Potato Dextrose Agar
(PDA) and oatmeal agar (OMA), and between growth
on Potato Dextrose Agar (PDA) and Coon’s agar (CN)
is much smaller.
4. Discussion
Temperature is one of the basic environmental
parameters inuencing fungal growth. Growth of most
Table 4. Production of pycnidia of Ascochyta spp. under different growth conditions (medium, temperature, light).
+ observed pycnidium production, - no pycnidium production observed
Species Isolate
Presence of pycnidia
CN/OMA/PDA medium at temperatures PDA medium/light
5ºC 10ºC 15ºC 20ºC 25ºC 20ºC
A. agrostidis C758.97 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. avenae 1982 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. avenae C811.84a –/–/– –/–/– –/–/– –/–/– –/–/– –
A. brachypodii 1155 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. brachypodii 1523a/2 –/–/– –/–/– –/–/– –/–/+ +/+/– +
A. brachypodii 1968a –/–/– –/–/– –/–/– –/–/– –/–/– –
A. desmazieri C247.79 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. digraphidis 1968b –/–/– –/–/– –/–/– –/–/– –/–/– –
A. ducis-aprutii 1915 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. festucae C689.97 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. graminea C586.79 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. hordei 1684 –/+/– –/+/– –/+/– –/+/+ +/+/– +
A. hordei 1971 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. hordei 770b –/–/– –/–/– –/–/– –/–/– –/–/– –
A. hordei var. americana C814.84 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. hordei var. europea C817.84 –/+/– +/+/+ –/+/– +/+/– +/+/– –
A. hordei var. hordei C878.72a –/–/– –/–/– –/–/– –/–/– –/+/– –
A. melicae 2010 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. melicae 793c –/–/– –/–/– –/–/– –/–/– –/–/– –
A. phleina C517.74 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. skagwayensis C110124 –/–/– –/+/– –/+/– +/+/+ +/+/– +
A. sorghi C622.68 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. stipae 1811 –/–/– –/–/– –/–/– –/–/– –/–/– –
A. zeicola 1937 –/–/– –/–/– –/–/– –/–/– –/–/– +
1081

In vitro
growth of some species of
Ascochyta
Lib.
fungi is observed within a temperature range of 5-30ºC.
Frequently, the pathogen and the host plant have similar
temperature requirements. For instance, A. zeicola has
the highest optimal growth temperature (24.2ºC) of all
the analyzed fungi, and its occurrence was recorded
on Saccharum ofcinarum and Zea mays, which
are thermophilic plants. Ascochyta stipae (synonim
A. antarctica) and A. ducis-aprutii were isolated from
plants growing in Antarctica [2], and lower temperature
optimums of approx. 15ºC were found for these species.
The capacity to produce pycnidia was observed under
different temperature and lighting conditions, but only in
scarce species/isolates. Roger and Tivoli [11] found the
formation of pycnidia and perithecia at 20ºC, and under
light conditions in the related species Mycosphaerella
pinodes (anamorph of Ascochyta pinodes). They did
not observe sporulation at lower temperatures or in the
dark. As in our study, Roger and Tivoli [11] found a high
variation in the production of fruit bodies in individual
isolates and a high suitability of oatmeal agar for
pycnidium production. Zhao et al. [12] investigated the
effect of temperature on the growth of A. rhei on PDA,
and found the fastest growth to occur at 22ºC. It was
noted that spot disease of rhubarb (Rheum rhaponticum)
is observed only in hot summers [12]. The relationship
between optimal temperatures for in vitro fungal
growth and the occurrence of optimal temperatures
in rhubarb plantations suggests that we may expect a
similar dependence in the case of other plant species.
Didymella rabiei (anamorph of Ascochyta rabiei) shows
different growth rates at 15ºC and 25ºC, depending on
the place of origin and cultivation method adopted for
the host plants. Some isolates of common origin exhibit
the same growth rates at both temperatures. Our results
suggest growth rates consistent with those of other
isolates, with faster growth recorded at 25ºC than at
15ºC [13]. Didymella rabiei is a pathogen of chickpea,
but its occurrence was reported also on other plants,
including wheat [14].
In recent years, fungi from the genus Ascochyta
were identied as causes of wheat leaf necrosis in a
variety of locations globally [15,16]. At the same time, a
lack of reports on the subject and a very limited number
of conrmations by the same authors on the occurrence
of these pathogens in successive years indicate a very
specic pathogen-plant-environment dependence.
It seems that a specic system of temperature and
humidity as well as the large-scale cultivation of a
susceptible cultivar is important for the appearance
of disease. Under these optimal conditions, the area
of necrosis on wheat leaves may reach as much
as 45% (articial inoculation [16]). In New Zealand,
the occurrence of A. hordei was reported on barley,
A. sorghi on brome grass and wheat, A. avenae on oat
and A. tritici on wheat [4].
Boerema et al. [5] identied A. avenae,
A. desmazieresii, A. tritici and Didymella exitialis as
causes of leaf spot in barley, wheat and rye grasses,
while additionally mentioning A. hordei var. hordei as the
agent of leaf spot in barley. It is reported that the role of
these fungi in the incidence of spot diseases in cereals
has been increasing, particularly in humid years. Since
fungal growth depends on both the type of medium and
temperature, these fungal species may have different
nutrient requirements. In practice, it may mean that
plant infestation will depend on the species, cultivar, and
even age or nutrient status of the plant. In terms of the
effect of light on fungal growth, none of the isolates grew
faster in the light than in the dark. On the other hand, it
is commonly known that light is required for sporulation
in most fungi. However, our results also showed that
several isolates were able to produce pycnidia both in
the dark and in the light with the exception of A. zeicola
(1937), which sporulated only in the light. A faster growth
of fungi in the dark or a markedly superior growth of some
fungi in the dark rather than in the light may predispose
them to occurring on the lower leaves of plants where
there is greater shading. It needs to be stressed that
differing responses to light is a trait specic to isolates
rather than species, For example, A. brachypodii (1155,
1968a) grows much better in the dark than in the light,
as opposed to A. brachypodii (1523a/2), which grows at
similar rates in the dark and in the light.
A high positive correlation of fungal growth on OMA
and CN media, and at the same time a much weaker
correlation of growth on both these media with the growth
rate on PDA medium indicate a similar growth trend for
the analyzed fungi on both these media. Additionally,
the formation of pycnidia on these media conrms a
particular suitability of OMA and CN media for culture of
pycnidium-forming fungi, including Ascochyta sp.
Acknowledgements
The studies were conducted thanks to the co-nancing
of the Ministry of Science and Higher Education within
the framework of project no. N N310 086136.
1082

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