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Aggressiveness of eight Didymella rabiei isolates
from domesticated and wild chickpea native to Turkey
and Israel, a case study
Hilal Ozkilinc &Omer Frenkel &Dani Shtienberg &
Shahal Abbo &Amir Sherman &
Abdullah Kahraman &Canan Can
Accepted: 20 June 2011 / Published online: 7 July 2011
#KNPV 2011
Abstract Ascochyta blight, caused by Didymella
rabiei, affects both domesticated chickpea and its
congeneric wild relatives. The aim of this study was
to compare the aggressiveness of D. rabiei isolates
from wild and domesticated Cicer spp. in Turkey and
Israel on wild and domesticated hosts from both
countries. A total of eight isolates of D. rabiei
sampled from C. pinnatifidum,C. judaicum and C.
arietinum in Turkey and Israel was tested on two
domesticated chickpea cultivars and two wild Cicer
accessions from Turkey and Israel. Using cross-
inoculation experiments, we compared pathogen
aggressiveness across the different pathogen and host
origin combinations. Two measures of aggressiveness
were used, incubation period and relative area under
the disease progress curve. The eight tested isolates
infected all of the host plants, but were more
aggressive on their original hosts with one exception;
Turkish domesticated isolates were less aggressive on
their domesticated host in comparison to the aggres-
siveness of Israeli domesticated isolates on Turkish
domesticated chickpea. C. judaicum plants were
highly resistant against all of the isolates from
different origins except for their own isolates.
Regardless of the country of origin, the wild
isolates were highly aggressive on domesticated
chickpea while the domesticated isolates were less
aggressive on the wild hosts compared with the
wild isolates. These results suggest that the aggres-
siveness pattern of D. rabiei on different hosts could
have been shaped by adaptation to the distinct
ecological niches of wild vs. domesticated chickpea.
Eur J Plant Pathol (2011) 131:529–537
DOI 10.1007/s10658-011-9828-9
H. Ozkilinc :C. Can
Department of Biology, The University of Gaziantep,
Gaziantep 27310, Turkey
O. Frenkel :S. Abbo
The Levi Eshkol School of Agriculture,
The Hebrew University of Jerusalem,
Rehovot 76100, Israel
O. Frenkel :A. Sherman
Genomics Department, The Volcani Center,
Agricultural Research Organization,
Bet Dagan 50250, Israel
D. Shtienberg (*)
Department of Plant Pathology and Weed Research,
The Volcani Center, Agricultural Research Organization,
Bet-Dagan 50250, Israel
e-mail: danish@volcani.agri.gov.il
A. Kahraman
Faculty of Agriculture, Department of Field Crops,
Harran University,
Sanliurfa 63100, Turkey
Present Address:
H. Ozkilinc
Department of Plant Pathology,
Washington State University,
Pulman, WA 99164, USA
Keywords Ascochyta blight .Disease severity .Host
adaptation .Incubation period .Wild Cicer
Introduction
Chickpea (Cicer arietinum L.) was first domesticated
in southeastern Turkey (Ladizinsky and Adler 1976;
Lev-Yadun et al. 2000), where it is grown sympatri-
cally with its wild progenitor C. reticulatum and a
number of other annual Cicer spp. including C.
pinnatifidum, C. bijigum and C. echinospermum
(Ladizinsky and Adler 1976; Berger et al. 2003; van
der Maesen et al. 2005). Following the Neolithic
agricultural revolution, the chickpea crop spread in all
directions throughout the east Mediterranean and
reached the southern Levant within one millennium
(Gopher et al. 2001) where it became sympatric with
wild C. judaicum (Ben-David et al. 2006). C.
pinnatifidum and C. judaicum are closely related but
have an allopatric distribution (Ladizinsky and Adler
1976). C. pinnatifidum grows wild in Turkey (mainly
in southeastern Turkey), Syria and Lebanon while C.
judaicum grows in Israel and Jordan (van der Maesen
et al. 2005). The two wild species grow in rocky
habitats (of limestone or igneous bedrock) and are
part of the annual elements of dwarf shrub formation
in the hilly parts of the east Mediterranean (Ladizinsky
and Adler 1976;Bergeretal.2003; Ben-David et al.
2006). Natural ecosystems have greater environmental
heterogeneity, higher species diversity and lower host
density than agricultural systems (Burdon et al. 2006;
Stukenbrock and McDonald 2008). Often, the different
ecological characteristics of natural and agricultural
ecosystems impose different selection pressures on the
host plants and their respective plant pathogens
(Burdon et al. 2006;Abboetal.2007; Stukenbrock
and McDonald 2008).
Ascochyta blight caused by Didymella rabiei
(anamorph: Ascochyta rabiei) affects all above-
ground parts of both domesticated chickpea (Nene
1984; Akem 1999) and its wild relatives C. pinnati-
fidum (Can et al. 2007) and C. judaicum (Frenkel et
al. 2007). Under environmental conditions that favour
development of the pathogen, domesticated chickpea
crops are destroyed and yield losses can reach 100%
(Nene 1984;Akem1999; Muehlbauer and Chen
2007). In contrast, Ascochyta blight in natural
ecosystems occurs rarely and usually does not
devastate its wild Cicer hosts (H. Ozkilinc, unpub-
lished; Frenkel et al. 2007). Hence, the destructive
pathogens affecting domesticated chickpea may have
evolved from an ancestral population infecting wild
congeneric and conspecific host species and have
become more aggressive under domestication (Harlan
1976). This may have happened due to differences in
plant density, the genetic structure of the cultigen,
seasonal profiles of wild vs. domesticated chickpea,
environmental and/or ecological characteristics of
agricultural and natural ecosystems (Abbo et al.
2003,2007).
Differences in genetic markers, lack of gene flow
and differences in in vitro temperature responses of
colony hyphal growth have been documented among
D. rabiei sampled from domesticated and wild Cicer
spp. (Frenkel et al. 2010; Ozkilinc et al. 2010). This
was interpreted as evidence for the selective role of
the distinct ecologies of wild vs. domesticated
chickpea systems in shaping the adaptive and aggres-
siveness pattern of D. rabiei (Frenkel et al. 2010;
Ozkilinc et al. 2010). Recently, Frenkel et al. (2007)
showed that D. rabiei isolates sampled from Israeli C.
judaicum are capable of infecting a number of annual
wild and domesticated Cicer species under laboratory
conditions. However, several of the wild annual Cicer
species tested are native to Turkey and do not occur
naturally in Israel. Indeed, Turkey is an important
centre of diversity for Cicer spp. (Berger et al. 2003).
As such it also may be the centre of diversity of its
pathogens (Leppik 1970), suggesting that different
patterns of Cicer spp.-D. rabiei interactions may be
seen in this area. Frenkel et al. (2008) also showed
that on a local scale in Israel, D. rabiei isolates
sampled from sympatric wild C. judaicum and
domesticated chickpea hosts were more aggressive
on their original host. In most cases parasite popula-
tions are expected to have higher mean fitness on
their sympatric hosts than on allopatric hosts (Kaltz
and Shykoff 1998, Gandon and Michalakis 2002;
Laine 2005). For example, Andrivon et al. (2007)
showed that French and Moroccan Phytophthora
infestans populations were better adapted to their
local potato cultivars than to allopatric potato culti-
vars. Therefore, it is advisable to investigate the
aggressiveness traits of D. rabiei isolates on a broader
regional scale, including wild and domesticated hosts
(sympatric and allopatric Cicer spp.) to better under-
stand the pathogen adaptation profile and its specific-
530 Eur J Plant Pathol (2011) 131:529–537
ity across the sympatric wild-domesticated Near
Eastern system.
In this work we studied a limited number of host-
pathogen combinations aimed at gaining empirical
evidences towards answering the following two ques-
tions: 1) what are the aggressiveness patterns of D.
rabiei isolates from different Cicer species hosts on
their sympatric and allopatric / wild and domesticated
hosts; and 2) do isolates sampled from wild Cicer or
from domesticated chickpea exhibit a similar level of
aggressiveness regardless their country of origin? We
tested the aggressiveness of D. rabiei isolates sampled
from both wild (C. judaicum and C. pinnatifidum)and
domesticated chickpea (C. arietinum) in Turkey and
Israel on susceptible C. pinnatifidum/C. judaicum
accessions and on susceptible domesticated chickpea
cultivars grown in Turkey/Israel.
Materials and methods
Fungal isolates
D. rabiei was sampled from infected wild and
domesticated chickpea hosts in Turkey and in Israel
(Frenkel et al. 2010; Ozkilinc et al. 2010). The sample
included two isolates from each of C. pinnatifidum
and C. arietinum in Turkey, and two isolates from
each of C. judaicum and C. arietinum in Israel
(Table 1). Chosen isolates were collected from areas
where wild Cicer and domesticated chickpea grow
side by side. We preferred to use the term “domesti-
cated isolates”for the isolates sampled from domes-
ticated chickpea and “wild isolates”for the isolates
sampled from wild Cicer spp. hosts.
The isolates were maintained as single-spore
colonies in Petri dishes containing potato dextrose
agar medium and were incubated in a growth chamber
at 19±1°C under alternating cycles of 12 h of light/
darkness. Isolates from wild Cicer spp. were trans-
ferred to chickpea meal agar medium to enhance
sporulation (Wilson and Kaiser 1995; Can et al. 2007;
Frenkel et al. 2010). Conidia suspensions of fourteen-
day-old colonies were used for inoculations in the
aggressiveness experiments.
Plant material
Two domesticated chickpea cultivars and two wild
Cicer spp. accessions from Turkey and Israel were
used in this study. Cultivar Cagatay was bred by The
Black Sea Agricultural Research Institute in Samsun,
Turkey, and, is known to be susceptible to D. rabiei
isolates sampled from the southeastern region of
Turkey (H. Ozkilinc, unpublished). Cultivar Spanish
White is highly susceptible to D. rabiei (Frenkel et al.
2008) and has been used in Israel for more than
half a century. C. pinnatifidum accession Cp2 from
Adiyaman,Turkey, (37°42′N and 37°58′E) and C.
judaicum accession Cj64 from Nahal Arava, Israel,
(31°54′Nand34°59′E), chosen from the collection
of Ben-David and Abbo (2005), are also susceptible
to D. rabiei (Frenkel et al. 2008; Ozkilinc 2010). 2–3
seeds were planted in 0.5-l pots and plants were
maintained in a greenhouse at 15–25°C under natural
light. Wild Cicer spp. seeds were scarified to
enhance germination. Domesticated chickpea plants
were grown for three weeks and wild Cicer spp.
plants were grown for four weeks under the same
conditions prior to inoculation.
Country Province Latitude Longitude Host Year Isolate Code
Turkey Kahramanmaras 37°48′37°29′Cicer arietinum 2006 Myp3.2
Adiyaman 37°78′37°61 2006 Ak4.7
Kahramanmaras 37°53′37°35′Cicer pinnatifidum 2005 Cp1.05
Adiyaman 37°66′38°32′2006 Cp2.06
Israel Judean foothills 31′41′34′59′Cicer arietinum 2004 Natif
Judean foothills 31′49′34′55′2005 Bakoa
Northwestern Samaria 32′34′35′04′Cicer judaicum 2005 Yw15
Northwestern Samaria 32′31′35′08′2007 Fahm5
Tab l e 1 Didymella rabiei
isolates sampled from Cicer
spp. in Turkey and Israel
Eur J Plant Pathol (2011) 131:529–537 531
Aggressiveness of D. rabiei isolates from wild
and domesticated hosts
Aggressiveness of the fungal isolates sampled from
domesticated chickpea and from wild Cicer spp. was
tested on all of the host plants. Plants were sprayed
with conidial suspension of the pathogen (3 × 10
5
spores ml
−1
) with an air pressure hand sprayer to run-
off. Water-sprayed plants of each cultivar/accession
were used as controls. Then, the plants were imme-
diately covered with two polyethylene bags to
maintain moisture and placed in a growth chamber
at 19±1°C under the same light conditions described
above. Bags were removed 24 h later and the plants
were kept in the same growth chamber for the
duration of the experiment. Each treatment [i.e.,D.
rabiei isolate (sampled from wild or domesticated
chickpea plants) × domesticated chickpea cultivar or
wild Cicer spp. accession] was repeated three times
(three replicates) and the experiment was conducted
twice.
The plants were examined 4, 5, 6, 7, 8, 9, 12, 16,
and 19 days after inoculation. Two aggressiveness
measures were used: the incubation period and the
relative area under the disease progress curve
(RAUDPC). The appearance of first disease symp-
toms was used as an estimation for the incubation
period (in days). All the aerial plant parts (stems,
leaflets and petioles) of each plant in each pot were
inspected and disease severity (i.e., the proportion of
affected plant area, in %) was determined visually. For
example if the affected plant area is ¼ of the total
plant material, the score is 25%; with nearly dead
plant (virtually no green parts visible) but still with a
green stem, the score is 90%. Because the last disease
assesments were carried out on day 16 for domesti-
cated chickpea cultivars and on day 19 for wild Cicer
spp. accessions, RAUDPC was calculated. The area
under the disease progress curve (AUDPC in % ×
days) was calculated using all disease-assesment
records. Then, RAUDPC was calculated as
“AUDPC/16×100”for domesticated chickpea culti-
vars and “AUDPC/19×100”for wild Cicer spp.
accessions. RAUDPC (in %) represents the intensity
of the disease over time. Data were analyzed by
ANOVA (analysis of variance) using JMP 5.0 soft-
ware for windows (SAS Institute, Cary, NC). To
enable analysis of variance, the disease severity
values were normalized by the arcsine square-root
transformation (Ahrens et al. 1990). The following
ANOVA model was used:
Y¼mþCI þPO þCP þCO þCI PO þCI
CP þCI CO þPO CP þPO CO þCP
CO þCI PO CP þCI PO CO þCI
CP CO þPO CP CO þCI PO CP
CO þpathogen isolate ½CI;POþexperiment;
where Y represents the aggressiveness measure variable
(i.e., incubation period or RAUDPC); μrepresents the
true mean; CI is the ‘country of isolate (isolates from
Turkey or Israel)’effect; PO is the ‘pathogen origin’
effect (isolates from wild Cicer or domesticated
chickpea); CP is the ‘country of host plant’effect, it
relates to the growth country (Turkey or Israel) of the
cultivars/accessions used in the study; CO is the
‘cultivar / accession origin’effect (wild Cicer or
domesticated chickpea host); the following terms are
their respective interaction effects; and pathogen isolate
(CI, PO) is the individual pathogen isolate effect nested
within country of isolate and pathogen origin. Multiple
comparisons of the means were done by the Tukey-
Kramer HSD test (α=0.05). Experiment effect was
insignificant for both incubation period (P= 0.90) and
RAUDPC (P=0.38) (Table 2). Therefore, the data from
both experiments were pooled and the results of both
experiments are shown in the present report.
Results
Typical Ascochyta blight symptoms developed on
petioles and stems of all the tested domesticated
chickpea cultivars and wild Cicer accessions from
both countries. No morphological differences were
observed between symptoms caused by isolates from
the different host/country origins. Disease symptoms
appeared 4–6 days after inoculation on the domesti-
cated chickpea plants and 5–10 days after inoculation
on the wild chickpea plants (Fig. 1). Disease severity
ranged from 48.3 to 92.4% on domesticated chickpea
plants and from 34.6 to 71.2% on wild chickpea
plants (Fig. 1).
The linear ANOVA model used to compare
aggressiveness of D. rabiei isolates from different
origins was highly significant for both incubation
532 Eur J Plant Pathol (2011) 131:529–537
period (P<0.0001) and RAUDPC (P<0.0001). The
model explained 56% and 67% of the variation in
incubation period and RAUDPC, respectively (Table 2).
The individual ‘pathogen isolate’effect nested within
‘country of isolate’and ‘pathogen origin’was not
significant for aggressiveness measures (Table 2), so
average values of the isolates from each country/host
origin (e.g., Turkish wild, Israeli wild, Turkish domes-
ticated and Israeli domesticated isolates) were used in
the analyses. The interaction “country of isolate ×
pathogen origin × country of host plant × cultivar/
accession origin”had a significant effect on both
studied measures and this interaction explained the
aggressiveness patterns of the isolates considering the
pathogen’s and host’sorigin(Table2,Fig.2).
Significant differences in incubation period were
mostly observed for the interaction of D. rabiei
with C. judaicum. Israeli isolates from C. judaicum
had the shortest incubation period (mean= 5.2 days)
on their own host (Fig. 2). Wild Turkish isolates had
long incubation periods (mean=9 days) on C.
judaicum plants. Both Turkish and Israeli isolates
from domesticated chickpea had the longest incuba-
tion period on C. judaicum plants (mean = 11 and
10 days, respectively).
The most severe infection developed when Israeli
domesticated chickpea plants were challenged with
Israeli domesticated isolates (mean RAUDPC = 51%,
Fig. 2). In comparison to Israeli domesticated isolates,
isolates from Turkish domesticated chickpea, C.
pinnatifidum and C. judaicum, were less aggressive
on Israeli domesticated chickpea (mean RAUDPC =
39%, 33%, 30%, Fig. 2). These mean RAUDPC
differences were found to be statistically significant
using a Student’sttest (data not shown).
Interestingly, Turkish domesticated isolates caused
the lowest level of disease (mean RAUDPC = 15%) on
their original host compared with the Israeli domes-
ticated, Israeli and Turkish wild isolates on the
Turkish domesticated chickpea plants (mean
RAUDPC=32, 22 and 19%, respectively).
Turkish and Israeli wild isolates were highly
aggressive on their own hosts (C. pinnatifidum and
C. judaicum, respectively) (mean RAUDPC =28%
and 31%, respectively) (Fig. 2). While Israeli wild
isolates were quite aggressive on C. pinnatifidum
(mean RAUDPC=17%), Turkish wild isolates
exhibited a significantly lower level of aggressiveness
on C. judaicum plants (mean RAUDPC = 8%) (Fig. 2).
Domesticated isolates from both Israel and Turkey
had significantly low levels of aggressiveness on both
C. pinnatifidum (mean RAUDPC=14% and 9%,
respectively) and on C. judaicum (mean RAUDPC =
13%, 10%, respectively) (Fig. 2).
Discussion
All of the tested isolates infected both wild and
domesticated chickpea plants, but were generally
more aggressive on their original hosts, suggesting a
certain degree of host adaptation (Fig. 1). Similarly,
Frenkel et al. (2010) found that isolates of D. rabiei
sampled from sympatric wild and domesticated
chickpeas in Israel were better adapted to their
original hosts. In our study, we found one exception
Table 2 Analysis of variance of aggressiveness measures
(incubation period and RAUDPC) of Didymella rabiei isolates
collected from domesticated and wild chickpea from Turkey
and Israel. Isolates’aggressiveness was evaluated on Turkish
and Israeli domesticated chickpea (C. arietinum) cultivars and
wild Cicer spp. (C. pinnatifidum &C. judaicum) accessions
Source Incubation
period
RAUDPC
ANOVA
Model <0.0001 <0.0001
R
2
0.557 0.670
Pvalues of each effect
Country of isolate (CI) 0.001 <0.0001
Pathogen origin (PO) 0.173 0.043
Country of host plant (CP) <0.0001 <0.0001
Cultivar / accession origin (CO) <0.0001 <0.0001
CI×PO 0.858 0.134
CI×CP 0.533 0.024
CI×CO 0.018 0.539
PO×CP 0.010 0.206
PO×CO <0.0001 <0.0001
CP×CO <0.0001 <0.0001
CI×PO×CP 0.047 <0.0001
CI×PO×CO 0.395 0.012
CI×CP×CO 0.043 <0.0001
PO×CP×CO 0.082 0.629
CI×PO×CP×CO 0.019 0.0007
Pathogen isolate [CI, PO] 0.405 0.104
Experiment 0.903 0.382
Eur J Plant Pathol (2011) 131:529–537 533
to the pattern of higher aggressiveness on the original
host of isolation; on the Turkish cultivar Cagatay,
Israeli domesticated isolates were more aggressive
than Turkish domesticated isolates (Fig. 1). However,
this finding needs to be treated with caution due to the
low number of isolates tested. Interestingly, Ozkilinc
et al. (2010) showed that Israeli domesticated isolates
had higher hyphal growth rates in vitro compared
with Turkish domesticated isolates. Therefore, it is
tempting to assume that the higher growth rate of
Israeli domesticated isolates in vitro is associated with
higher aggressiveness in vivo. A positive correlation
between in vitro radial growth and pathogenicity was
also observed in the Dutch elm disease fungus,
Ophiostoma ulmi (Brasier and Webber 1987). How-
ever, in vitro growth rate does not always correlate
with aggressiveness (Thrall et al. 2005; Pariaud et al.
2009).
The wild isolates were quite aggressive on domes-
ticated chickpea cultivars from both countries while
the domesticated isolates regardless of the country of
origin were less aggressive on the wild hosts. This
observation is consistent with the hypothesis that D.
rabiei infecting wild Cicer spp. gave rise to Asco-
chyta blight on domesticated chickpea at an early
stage of the crop’s evolutionary history (Abbo et al.
2003). The selection acting on D. rabiei populations
on domesticated chickpea, has presumably selected
isolates better adapted to domesticated chickpea and
less adapted to wild chickpea hosts (Abbo et al. 2003,
2007). This hypothesis is supported by the findings of
Frenkel et al. (2008) showing that, on a more resistant
Israeli cultivar Yarden, the Israeli domesticated iso-
lates had higher aggressiveness when compared with
the Israeli wild isolates. Our past work has shown that
isolates from domesticated chickpea are better adap-
ted to higher temperatures (Frenkel et al. 2008,2010;
Ozkilinc et al. 2010). This finding supports the
hypothesis that chickpea summer cropping has been
a traditional practise across the Levant to avoid the
winter conditions favouring Ascochyta blight (Abbo
et al. 2003). As a result, it is possible that the isolates
Time (da
y
after inoculation)
Disease severity (%)
Turkish domesticated
isolates
0
20
40
60
80
100
Israeli domesticated
isolates
0
20
40
60
80
100
Turkish wild isolates
0
20
40
60
80
100
Israeli wild isolates
0
20
40
60
80
100
0 4 8 12 16 20 0 4 8 12 16 20
0 4 8 12 16 20 0 4 8 12 16 20
Fig. 1 Disease progress curves of Didymella rabiei isolates
from different host/country origins (Turkish & Israeli / wild &
domesticated Cicer spp.) on: the Turkish chickpea cultivar
Cagatay (■); Israeli chickpea cultivar Spanish white (□-);
Turkish C. pinnatifidum accession Cp2 (●); Israeli C. judaicum
accession Cj64 (○-). The average disease severity values of the
two isolates randomly sampled from each host/country origin
(Turkish wild, Israeli wild, Turkish domesticated and Israeli
domesticated isolates) represents the average values of 6
replicates. Vertical lines represent the least significant differ-
ences for the examined dates where differences among hosts
were significant at P=0.05, as determined by the Tukey-Kramer
HSD test
534 Eur J Plant Pathol (2011) 131:529–537
from domesticated chickpea have evolved to become
better adapted to hotter temperatures and are therefore
better competitors and colonizers on the cultigen in its
man-managed habitats. Still, both wild and domesti-
cated host plants may serve as a potential source of
inoculum for each other via pathogen migration
during the season, especially (but not exclusively) in
sympatric systems. Very limited gene flow was
observed between D. rabiei infecting wild C. judai-
cum and domesticated chickpea (Ozkilinc et al. 2010).
Gene flow may hinder local/host adaptation, but
effective gene flow depends on both the performance
of the immigrants and the fitness of their offspring
and later-generation descendants (Kawecki and Ebert
2004). Interestingly, a significant decrease in patho-
genic fitness was detected among the progeny of
crosses between Israeli D. rabiei isolates sampled
from wild and domesticated hosts in laboratory con-
ditions (Frenkel et al. 2010), thereby suggesting that the
restricted gene flow between the sympatric wild and
domesticated D. rabiei isolates does not prevent the
slow evolution of host specificity in the domesticated
chickpea-wild Cicer spp. system (Frenkel et al. 2010).
Such a phenomenon was also recorded in other
pathosystems such as the Heterobasidion annosum
species complex in California, where pathogen hybrids
were less adapted to the host species compared with
their parental isolates (Garbelotto et al. 2007).
Tr dom.
isolates
×
Cj
Is dom.
isolates
×
Cj
Incubation Period (days)
Tr wild
isolates
×
Cj
Tr wild
isolates
×
Tr Ca
Tr dom.
isolates
×
Cp
Is wild
isolates
×
Tr Ca
Is wild
isolates
×
Is Ca
a
a
ab
bc bc cc
ccc
ccc
ccc
0
2
4
6
8
10
12
Tr dom.
isolates
×
Tr Ca
Is wild
isolates
×
Cp
Tr wild
isolates
×
Cp
Tr wild
isolates
×
Is Ca
Is wild
isolates
×
Cj
Is dom.
isolates
×
Cp
Tr dom.
isolates
×
Is Ca
Is dom.
isolates
×
Is Ca
Is dom.
isolates
×
Tr Ca
(a)
a
ab
ab ab ab bbc
bcd cde cde de de de de ee
0
10
20
30
40
50
60
RAUDPC (%)
Tr dom.
isolates
×
Is Ca
Is dom.
isolates
×
Is Ca
Is wild
isolates
×
C
j
Is wild
isolates
×
Is Ca
Is dom.
isolates
×
Tr Ca
Tr wild
isolates
×
Is Ca
Tr wild
isolates
×
C
p
Is wild
isolates
×
Tr Ca
Tr wild
isolates
×
Tr Ca
Is wild
isolates
×
C
p
Tr dom.
isolates
×
Tr Ca
Is dom.
isolates
×
C
p
Is dom.
isolates
×
C
j
Tr dom.
isolates
×
C
j
Tr dom.
isolates
×
C
p
Tr wild
isolates
×
C
j
(b)
Fig. 2 a Incubation period and (b) RAUDPC values of each
pathogen-isolate combination (from Turkish (Tr)/Israeli (Is)
domesticated (dom.)/wild host origin) on each host origin
(Turkish/Israeli domesticated and wild Cicer spp.). Columns
were coloured according to the host type in the interaction
[empty/C. judaicum (Cj), black/C. pinnatifidum (Cp), dark
grey/ Turkish C. arietinum (Tr Ca), light grey/Israeli C.
arietinum (Is Ca)]. Values in the same column followed by the
same letter are not statistically different (P=0.05) according to
the Tukey-Kramer HSD test
Eur J Plant Pathol (2011) 131:529–537 535
Interestingly, C. judaicum plants were resistant to
all of the isolates from different origins, but not to
their own isolates. Isolates from C. judaicum had
shorter incubation periods and higher RAUDPC
values compared with the isolates sampled from other
sources on C. judaicum plants. Frenkel et al. (2008)
also showed higher aggressiveness of D. rabiei
isolates from C. judaicum on their own host compared
with the isolates from domesticated hosts. It is
interesting to speculate on the mechanisms driving
higher aggressiveness of C. judaicum isolates on C.
judaicum compared with the isolates from other hosts.
One hypothesis is that C. judaicum has had a long
evolutionary history of geographic (and ecologic)
isolation from other congeneric Cicer species and
possibly also their D. rabiei pathogens. A number of
wild annual and perennial Cicer spp. are known from
the Balkans, Turkey, Syria, Lebanon, Iraq, Iran and in
Central Asia. C. judaicum however, is known only
from Israel and Jordan and no other wild Cicer spp.
are native to these two countries. C. judaicum is
found in drier and hotter environments compared with
the above-mentioned taxa (Berger et al. 2003). Host–
parasite co-evolution processes are tightly coupled
with parasite adaptation to the abiotic environment,
thereby affecting strength, and even direction, of
speciation and local adaptation to temperature (Laine
2008). In the southern Levant, similar effects may
have selected for wild D. rabiei pathogens with
environmental requirements closer to that of domes-
ticated chickpea. A larger sampling from annual and
perennial wild Cicer species and their Ascochyta
pathogens is required for a deeper understanding of
the C. judaicum-D. rabiei interaction. At present, we
have no information on the genetic control of
aggressiveness in the pathogen nor on the genetic
basis of resistance in the wild hosts. Advances in
understanding host-pathogen co-evolutionary interac-
tions requires integrating knowledge of the molecular
basis of host resistance and pathogen virulence
(Burdon and Thrall 2009).
Our results have shown that aggressiveness pat-
terns differ among D. rabiei isolates from wild and
domesticated hosts and suggest that the distinct
ecology of wild vs. domesticated chickpea shapes
the aggressiveness pattern of D. rabiei resulting in
differential adaptive (phenotypic) and genetic struc-
ture across the wild-domesticated pathosystem. This
is in line with the reports of Frenkel et al. (2010) and
Ozkilinc et al. (2010) on different ecologically
adaptive traits and the molecular divergence of D.
rabiei from wild and domesticated hosts. While these
results provide some clues about the Cicer-D. rabiei
pathosystem in wild and domesticated / sympatric and
allopatric formations, a larger number of isolates
should be studied to obtain deeper understanding of
aggressiveness and host/local adaptation patterns of
the pathogen and its wild and domesticated hosts.
Acknowledgements The authors would like to thank Profs.
Avigdor Cahaner and Yonathan Elkind (Institute of Plant
Science, Hebrew University, Rehovot, Israel) for their valuable
statistical advice and Dr. Tobin Peever (Department of Plant
Pathology, Washington State University, Pullman, USA) for his
valuable comments. We would like to thank Mr. Haim Vintal for
technical assistance. The work of Dr. H. Ozkilinc in Drs.
Sherman and Shtienberg laboratories was made possible by a
research scholarship granted to H. Ozkilinc by the Israeli
Ministry of Foreign Affairs.
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