American Journal of Plant Sciences, 2011, 2, 457-460
doi:10.4236/ajps.2011.23053 Published Online September 2011 (
Copyright © 2011 SciRes. AJPS
Evaluation of the Incidence and Severity of Olive
Leaf Spot Caused by Spilocaea oleagina on Olive
Trees in Palestine
Mazen Salman1*, Abd-Almonem Hawamda1, Ahmad Al-Ashqar Amarni1, Mahmoud Rahil1,
Hajaj Hajjeh1, Basel Natsheh1, Ruba Abuamsha2
1Technical and Applied Research Center (TARC), Palestine Technical University-Kadoorie (PTUK), Tulkarm, West Bank, Palestine;
2National Agriculture Research Center (NARC), Jenin, West Bank, Palestine.
Email: *
Received June 18th, 2011; revised July 14th, 2011; accepted August 22nd, 2011.
Olive Leaf Spot (OLS) is found in many parts of the world and cause readuced growth and yield in olive trees. In this
study, investigations were carried out to measure the incidence (% infected leaves) and severity (number of lesions/leaf)
of OLS in olive growing regions in Palestine, including the regions of Hebron, Bethlehem, Tulkarm, Salfit, Jenin,
Nablus, Ramallah and Qalqilyah. OLS was found in all study areas with significa ntly higher percent incidences in Jenin
and Nablus (67.16% ± 18.16% and 46.06% ± 23.70%, respectively). OLS was more severe in Nablus, Qalqilyah, Jenin
and Tulkarm (severity grade 3.0 - 3.7). Analysis indicate that there is a positive correlation (R2 = 0.597) between dis-
ease incidence and severity. OLS appeared to be particularly severe on trees that were growing in regions with higher
annual rainfall. The correlation between severity and rainfall was positive (R2 = 0.543).
Keywords: Palestine, Spil ocaea oleagina, Peacock Spot, Disease Severity, Olea Europaea
1. Introduction
Olive tree (Olea eu ropaea L.) is the most important fruit
tree in Palestine covering approximately 45% of the Pal-
estinian agricultural land [1]. The tree is distinctly im-
portant in the economic and social life of the people,
comprising one of the main sources of income, reaching
its contribution to the good years to about 13% of the
annual agricultural production [1]. One of the most
widespread fungal diseases on olive trees is the Olive
Leaf Spot (OLS), also known as Peacock Spot disease
caused by the fungus Spilocaea oleagina (Castagne)
Hughes [2].
The disease is common worldwide and serious in
cooler olive-growing regions, with yield losses estimated
up to 20% [2]. The principal symptoms of OLS are dark
green to black spots surrounded by a yellow halo on
leaves. Petioles, fruit and stems are susceptib le but rarely
have lesions [3]. The disease causes severe premature
defoliation of olive, and sometimes leads to twig death
resulting in a subsequent loss in crop yield [4]. Infection
of fruit can delay in ripening and a decrease in oil yield,
causing unacceptable blemishes on table olives [2].
Chemical fungicides are the principal method used to
control OLS throughout olive-growing regions of the
world. In o live-growing regions, which are characterized
by long dry summers, OLS is controlled by application
of copper-containing fungicides prior to winter rains [3].
However, timing of the fungicide applications was re-
ported to be critical for effective control of the disease
[5]. In additoin to that, the use of fungicides against the
disease is limitted beacuase of their high costs and possi-
ble effects on human health and the environment. Re-
gardless of material, the application rate or number of
applications, copper containing fungicides will control
OLS when disease risk is low [3]. Moreover, regular an-
nual treatment is required to prevent disease build-up in
the grove, as high disease levels may be difficult to re-
duce [6].
Control of OLS disease in Palestine is limited due to
the lack of control methods, and due to the fact that the
costs of control will reduce the economic income of the
farmers. Many copper products are used to reduce infec-
tion of the disease. However, the Palestinian farmers
avoid spraying in order to keep the production of olive
oil devoid from chemicals advantage. Despite the high
Evaluation of the Incidence and Severity of Olive Leaf Spot Caused by Spilocaea oleagina on Olive Trees in Palestine
importance of olive tree in Palestine, little informations
are available about pests and diseases attaking the tree.
The aim of this work was to conduct a field survay to
assess the incidence (% infected leaves) and severity
(number of lesions/leaf) of OLS in different regions in
2. Materials and Methods
A field assessment was conducted during the summer
2010 on olive trees in different regions in Palestine in-
cluding Hebron, Bethlehem, Ramallah, Nablus, Qalqilyah,
Tulkarm, Salfit, Jenin and Tubas (Figure 1). About 20
trees (20 - 30 years old) from infested groove in each
district were sampled randomly. On each tree, 100 leaves
were randomly selected on the surrounding four sides of
the tree and taken to the laboratory for evaluatio n of dis-
ease incidence and severity. Leaves were dipped in 5%
NaOH for 5 min and the number of lesions was counted.
Disease incidence was determined by recoding the per-
cent of infected leaves per tree. For disease severity, the
number of lesions per leaf was counted and graded; 1 (1
lesion), 2 (2 lesions), 3 (3 - 5 lesions), 4 (6 - 10 lesions)
or 5 (> 11 lesions) [7].
For statistical analysis, data on the percent of infected
leaves were Log-transformed. All data were analyzed for
variance by Analysis of Variance (ANOVA). Significant
differences among treatments were computed after
Tukey HSD test at P < 0.05.
Figure 1. Map of the West Bank and the regions surveyed.
3. Results
It was found that all regions are infected with the Olive
Leaf Spot disease (OLS). Investigations showed that
three (Hebron, Bethlehem and Tubas) of the nine regions
surveyed have lowest percentage of leaves infected with
OLS (F = 8.73, df = 8, P < 0.05) (Figure 2). The highest
disease incidence was recorded in Jenin (67.2%) fol-
lowed by Nablus (46.06%). The lowest incidence (11.3%)
is measured in Tubas (Figure 2).
The disease severity (Figure 3) was also calculated for
OLS in all regions. The severity is significantly different
between regions (F =9.17, df = 8, P < 0.05). Higher se-
verity (grade 4) was recorded in Nablus and Qalqilyah
followed by Jenin, Tulkarm, Salfit and Ramallah (grade
3). The lowest disease severity was recorded in Tubas
and Bethlehem (grade 2) followed by Hebron (grade 1).
Figure 2. Disease incidence of Olive Leaf Spot (OLS) in
different regions in Palestine. Data with different letters are
significantly different after Tukeys HSD test using ANOVA
at P < 0.05.
Figure 3. Severity of Olive Leaf Spot (OLS) in different
regions in Palestine. Data with different letters are signifi-
cantly different after Tukeys HSD te st using ANOVA at P <
Copyright © 2011 SciRes. AJPS
Evaluation of the Incidence and Severity of Olive Leaf Spot Caused by Spilocaea oleagina on Olive Trees in Palestine459
The relationship between disease incidence and dis-
ease severity is described by a linear regression (Figure
4). A positively significant correlation (R2 = 0.597) was
recorded between incidence and severity.
Interestingly, the prevalence of OLS significantly in-
creases with the mean annual rainfall (Figure 5). The
relationship (R2 = 0.543) between rainfall and disease
incidence was positively correlated (Figure 5).
4. Discussion
Olive Leaf Spot (OLS) disease is found in many parts of
the world and was recognized in the Mediterranean areas
for over a century [8]. The assessment of OLS levels is
Figure 4. Relationship between disease incidence (% of in-
fected leaves and severity (number of lesions per leaf) across
all trees and assessment regions.
Figure 5. Relationship between mean annual rainfall and
disease incidence. Annual rainfall data were obtained from
the Palestinian M eteorological Dep a r tme nt website.
usually indicated by incidence or severity [9]. For many
plant diseases, severity is considered to give an accurate
indication of disease effect on plants [9]. However, vis-
ual estimation of disease severity can vary between as-
sessors whereas assessment of disease incidence is faster
and more objective [10]. In this study disease incidence
(percent of infected leaves) and disease severity (number
of lesions per leaf) were investigated in different regions
of Palestine. The results showed a positive correlation
between disease incidence and severity.
According to this study, higher disease incidences and
severities were recorded in Jenin, Nablus, Tulakrm,
Qalqilyah and Salfit. The higher incidence in these re-
gions could be attribu ted to the wet and humid cond ition s.
The annual rainfall in these regions ranges, approxi-
mately, from 494 to 558 mm per year [11]. Cool and
moist environmental conditions are favored for epedimic
development of the fungus in cooler olive-growing re-
gions [2,12]. Moist weather conditions favor S. oleagina
sporulation, conidium germination and infection [2,12].
It was reported by Obanor et al. (2008) that conidium
production was optimal at 15˚C under high humidity
(100%), whereas conidium germination and infection
required continuous free moisture for 12 - 24 h and tem-
peratures ranging from 5˚C to 25˚C [13]. The results of
this study are in good agreement with the findings of
Obanor et al. (2008) who reported abundant conidium
production during spring and autumn, but limited co-
nidium production during the summer months.
To the Authors’ knowledge, the present study was the
first of its kind, in regard to surveying of disease inci-
dence and severity of OLS in Palestine. Epidemiological
studies are needed to determine the latent infection of
olive trees by the disease and to assess in more details the
climatic conditions for disease development under the
Palestinian environmental conditions. This will then en-
able to plan a control strategy of disease using chemical
fungicides and/or tree management strategies and devel-
opment of a disease forecasting system [14]. The effect
of OLS on tree health, fruit yield and olive oil quality
also requires further evaluation. This survey was con-
ducted during autumn season and only provides a pre-
liminary assessment of prevalence of OLS during this
This study showed that OLS is widely spread in Pales-
tine with all regions being infected. However, further
monitoring is needed to better understand the disease
incidence and spread in Palestine.
5. Acknowledgements
The Authors would like to thank Dr. Azmi Awad, Pales-
tine Technical University—Kadoorie (PTUK)) for facili-
tating this work by providing the university car. Thanks
Copyright © 2011 SciRes. AJPS
Evaluation of the Incidence and Severity of Olive Leaf Spot Caused by Spilocaea oleagina on Olive Trees in Palestine
Copyright © 2011 SciRes. AJPS
also are due to Dr. Hilmi S. Salem, PTUK for his con-
structive and objective comments on the manuscript. We
would like to thank Mr. Eng. Fares Jabi and the director-
ates of the Palestinian Ministry of Agriculture for Guid-
ance and help during the project.
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