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Advances in Environmental Biology, 6(2): 621-624, 2012
ISSN 1995-0756
This is a refereed journal and all articles are professionally screened and reviewed
ORIGINAL ARTICLE
First Report of Alternaria Leaf Spot on Gerbera (Gerbera Jamesonii L.) in North of Iran
Shokooh Farhood and Shervin Hadian
Young Researchers Club, Gorgan, Islamic Azad University, Gorgan, Iran.
Shokooh Farhood, Shervin Hadian; First Report Of Alternaria Leaf Spot On Gerbera (Gerbera
Jamesonii L.) In North Of Iran.
ABSTRACT
Gerbara is a genus of ornamental plants from the sunflower Asteracea family with great commercial value
which grown in several areas of the world. Alternaria leaf spots of gerbera (Gerbera jamesonii L.) were
observed on plants from different greenhouses in north of Iran. The sypmtoms at the initial stage of the infection
were brown, small, scattered spots on the leaves that gradually become round or irregular. Spots coalesce to
affect large areas of leaves and cause defoliation. Affected plants showed lower vitality, suppressed
development and fewer, smaller, distorted in shape flowers. Fungi isolates, obtained from infected leaf tissues
were grown in pure culture and on the base of morphological characteristics of colony and conidia, the pathogen
was identified as Alternaria alternata. The fungus produced effuse, olivaceous black colonies with dark olivegreen margins, and abundant branched septate, golden brown mycelium. The conidiophores were branched,
straight, pale brown to olive brown. The pale brown conidia of the isolates were catenated in long, sometimes
branched chains of 5-12 spores. The size of conidia varied from 20-63 µm in length and 9-18 µm in width and
usually ovoid to ellipsoid or obclavate with short conical beak at the tip. Conidia had two to three transverse
septa and usually several longitudinal septa. Pathogenicity tests conducted on healthy potted gerbera plants in a
glasshouse showed typical leaf spot symptoms after two weeks. This is the first report of a leaf spot disease of
gerbera in north of Iran.
Key words: Alternaria, conidia, Gerbera, leaf spot.
Introduction
Gerbera is one of the top ten cut-flower of the
world, It is a genus of ornamental plants from the
sunflower Asteracea family with great commercial
value, successfully grown under different condition
in several areas of the world [1]. Because of its
extensive cultivation and commercial importance
keeping quality and quantity is serious so diagnose
and control of diseases are necessary.
There are some published reports about disease
on gerbera: In Argentina in autumn 2007, a downy
mildew infection was observed on plants of gerbera
var. Avant Garde cultivated in greenhouses.
Symptoms began as irregularly shaped yellow
discoloration on the upper surface of the leaf, later
turning light to dark brown [23]. Powdery mildew
symptoms caused by Podosphaera sp. were observed
on the leaves of Gerbera jamesonii during April
2008 in an experimental field of India [2]. Powdery
mildew caused by Golovinomyces cichoracearum
was observed on potted gerbera growing in a private
garden in Italy [21]. In October, 1995, in North
America, white erumpent sori were detected on the
undersurfaces of leaves of a bed of Gerbera
jamesonii that diagnose as white rust [22]. Tomato
spotted wilt virus reported on Gerbera hybrida in
Serbia. The infected plants displayed chlorotic oakleaf patterns followed by necrosis and distortion of
leaves [19].
Alternaria leaf spot was reported in Bulgaria.
The symptoms of the disease on the leaves were
characterized by the development of brown, small,
scattered dots, which gradually enlarged and
coalesced to form large, oval, circular or irregular,
brown to black lesions with concentric rings [12].
Also Alternaria sp. on Barberis thunbergii cuase
stem spot showed dark brown, eye-like elongated
spots on stems and red and yellow spots on the
leaves [11]. Alternaria alternata cause a stem spot
disease on Gymnocalycium mihanovichii [10]. In
some greenhouses in north of Iran leaf spots with the
same symptoms have been observed on Gerbera
jamesonii. The objectives of this study were to
describe the symptomatology of this new leaf spot
disease of Gerbera jamesonii and to isolate and
identify the causal organism and confirm its
pathogenicity on healthy gerbara in greenhouses.
Corresponding Author
Shokooh Farhood, Young Researchers Club, Gorgan, Islamic Azad University, Gorgan, Iran.
E-mail: [[email protected]]
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Adv. Environ. Biol., 6(2): 621-624, 2012
Materials and Methods
Sampling and Isolation:
Gerbera leaves with leaf spot were collected
from five greenhouses in the north of Iran, they were
transported to the labrotary for isolating pathogenic
fungi. Leaves with spots were cut into small piece,
surface sterilized with 1% NaOCl for 1 minute rinsed
thoroughly in sterile distilled water and dried with
sterile filter paper. The leaf pieces were placed on to
potato dextrose agar (PDA) medium. The cultures
incubated at 25±1 °C for 10 days to promote fungal
growth and sporulation. The growth fungi was
isolated, and pure culture were obtained from single
spores and hyphal tips and maintained on potato
dextrose agar medium in plates.
The morphological and culture characteristic of
the isolated organism were studied also conidia and
conidiophores ditails were considered.
Pathogenicity Test:
Conidial suspension of the isolate was prepared
from fungi which growed for 10 days on PDA
cultures, and the conidial concentration was adjusted
to 2 × 105/ml using hemacytometer. The gerbera
plants were cultivated at regular intervals in pots
with sterile soil mixture and they were sprayinoculated with 100 ml of the spore suspension per
pot. Inoculated plants were placed in a humid
chamber with 100% relative humidity at 25°C for 24
hours. The plants were covered tightly with a
transparent nylon foil, after 24 hours plants were
uncovered and Constant humidity was maintained by
spraying tap water. The plants were grown in a
greenhouse (25–30°C) for 2 weeks for symptom
development. After 2 weeks typical symptoms were
produced on the inoculated leaves. The pathogen
from the infected leaves was re-isolated on PDA
medium as described above. The morphological and
cultural characteristics of the re-isolated organism
were compared with the original pathogen and they
were the same.
Result:
The symptoms of the disease on the leaves were
appearing by brown, small, scattered spots on the
leaves that gradually become round or irregular,
brown to black lesions, concentrically zonate with a
dark brown margin. In later stages of infection
affected leaves discolored to yellowing and finally
dried up. The infection appear from the older, lower
leaves and spread to upware. The percentage of
diseases incidence was 22.6% (7 spotty leaves in 31
healthy leaves). Necrotic spots were often numerous
and enlarged quickly to blight the leaf tissue
Circular, necrotic and sunken dark brown spots on
both side of the leaf, ranging from less than 20 mm
to an average diameter of 30 mm were typical
symptoms of disease (Fig1).
Fig. 1: The symptoms of Alternaria alternata on the leaf of Gerbera jamesonii.
The fungus produced flat, downy to woolly and
grey colonies with olive green peripheries. The
Alternaria grew well on PDA and formed an
olivaceous black colony with dark olive margins,
reverse black at 25±1 °C after 10 days. The surface
was greyish white at the beginning which later
darkens and became greenish black or olive brown.
The conidiophores were branched, straight, Pale
brown to olive brown in colour, measuring 25-60 μm
long and 3-3.5 μm thick. The conidia were pale
brown to light brown in colour and produced in long
branched chains, obclavate to obpyriform or ellipsoid
in shape with short conical beak at the tip, or
beakless. The size of conidia varied from 20-63 µm
in length and 9-18 µm in width. Conidia had two to
three transverse septa and usually several
longitudinal septa (Fig2).
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Adv. Environ. Biol., 6(2): 621-624, 2012
Fig. 2: Morphological characterestics of conidia.
Pathogenicity tests conducted on healthy potted
gerbera plants in a glasshouse showed as the same
typical leaf spot symptoms of the first isolation after
two weeks and enlarging necrotic areas developed on
gerbera leaf following inoculation after two weeks.
These results, based on morphological
characteristics and pathogenicity tests, confirm the
identity of the fungus as Alternaria alternata. This is
the first report of Alternaria alternata as leaf spot
disease of gerbera in north of Iran.
Discussion:
In this report we describe the symptomatology
of a new disease on gerbera at greenhouses in north
of Iran. Small, circular, necrotic and dark brown
spots on the leaves that gradually become larger and
irrigular were the typical symptoms of Alternaria
disease that it was agree with result of Long et al.,
[8] depicted brown, circular or oval spots. These
enlarged and linked together, extending until entire
leaves withered. Bajwa et al., [3] reported a leaf spot
disease on Aloe vera plants that observed as small,
circular to oval dark brown necrotic sunken spots on
the leaves. Leaf spot of gerbera was reported in
Bulgaria by Mirkova et al., [12] that observed brown,
small, scattered dots approximately 1 mm in
diameter. They gradually enlarged and coalesced to
form large (20–25 mm), oval, and circular to
irregular brown to black lesions with concentric
rings. Alternaria is a common plant pathogen, which
cuase a variety of fruit and plant disease. Previously,
Alternaria alternata reported in Iran from tangerine
that brown necrotic lesions surrounded by yellow
haloes, characteristic of Alternaria brown spot of
citrus, were found on young leaves and fruits [5].
Alternaria mali cuase apple leaf blotch that
symptoms included black and dark brown leaf spots
on leaves of apple trees [18]. Alternaria alternata on
wheat grains reported by Mirzadi Gohari et al., [13]
and Saberi Riseh et al., [16], and as a leaf spot
pathogen on potato [20].
In this study we observed the pale brown to
olive brown branched conidiophores with 25-60 μm
long and 3-3.5 μm thick, that was the same with
other results, the toxonomy of Alternaria alternata in
our studying is based on the morphology and
development of conidia and conidiophores and
colony morphology. The Alternaria alternata colony
grew well on PDA medium and formed an
olivaceous black colony with dark olive margins.
These morphological characters of the colony of the
present isolate coincide with those of colonies
described by Kamalakannan et al., [6] and Siddiqui
et al., [17].
Kamalakannan et al., [6] reported Alternaria
alternata as leaf spot on Aloe barbadensis, the
fungus produced conidiophores with branched,
straight, golden brown in colour, measuring 15 µm
long and 2-6 µm thick. Alternaria alternata isolated
from Chenopodium album produced conidiophores
simple, olive-brown, septate, variable in length with
terminal conidia, which are solitary or in short chains
[17]. The conidiophores of Alternaria alternata on
grafted cactus were solitary or in small fascicles,
commonly branched, pale brown, up to 60 µm long,
3-4.5 µm wide [10].
The conidia were pale brown to light brown in
colour and produced in long branched chains,
obclavate to obpyriform or ellipsoid in shape with
short conical beak at the tip, or beakless. The size of
conidia varied from 20-63 µm in length and 9-18 µm
in width and two to three transverse septa conidia
were observed. It is the same with report of
Alternaria alternata on Chenopodium album, the
fungus produced obclavate to obpyriform conidia
with a short conical or cylindrical apical beak not
exceeding one third of the conidial length, or
beakless, smooth walled or verruculose, slightly
constricted with 3-8 transverse septa, the lower part
each portion had one or two longitudinal septa [17].
Kamalakannan et al., [6] reported the size of conidia
of Alternaria alternata on Aloe barbadensis varied
from 22.75 to 63.70 µm in length and 13.65 to 18.20
µm in width with an average beak length of 7.73 µm.
Conidia had two to three transverse septa and usually
several longitudinal septa, that was according to our
result.
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Adv. Environ. Biol., 6(2): 621-624, 2012
As a species of the genus Alternaria,
Alternaria alternata belongs to the family of black
pigmented molds Dematiaceae. Alternaria alternata
has a wide host range, causing leaf spots and blights
on many plant parts [7].
According to our studying, this is the first report
of leaf spot disease, Alternaria alternata, of Gerbera
jamesonii in north of Iran.
11.
12.
Conclusion:
13.
It has been concluded from present research that
one of the most important factors which disappearing
small, circular, necrotic and dark brown spots on the
leaves of Gerbera jamesonii could be influence of
Alternaria alternata which belongs to Dematiaceae
family.
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