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Chickpea Ascochyta Blight: Disease Status and Pathogen Mating Type Distribution in Syria
Abstract
Chickpea fields were surveyed in nine major chickpea-growing provinces of Syria in 2008 and 2009 to determine the prevalence and severity of Ascochyta blight, and the distribution of Didymella rabiei mating types (MATs) in the country. A total of 133 Ascochyta rabiei isolates were assayed for mating type, including isolates from older collections that date back to 1982. Multiplex MAT-specific PCR with three primers was used for MAT analysis. Out of the 133 tested isolates, 64% were MAT1-1 and 36% were MAT1-2. Both MATs were found in six provinces but MAT1-1 alone was found in three provinces. Chi-squared analysis was used to test for a 1 : 1 ratio of MAT frequencies in all samples. The MAT ratios in the six provinces were not significantly different from 1 : 1, suggesting that there is random mating of the pathogen population under natural conditions. The presence of the two MATs is expected to play a role in the evolution of novel virulence genes that could threaten currently resistant chickpea varieties. Overall analysis of the 133 isolates showed a significant deviation from the 1 : 1 ratio with almost twice as many MAT1-1 isolates than MAT1-2 isolates, which indicates a competitive advantage associated with MAT1-1 in Syria. However, the overall picture of an unequal frequency in MATs indicates that there may be limited sexual recombination occurring in the Syrian population.
... The two mating types required for sexual reproduction have been referred to as MAT1–1 and MAT1–2 (Trapero-Casas & Kaiser 1992; Wilson & Kaiser 1995; Turgeon & Yoder 2000; Omar et al. 2011). In Syria, out of the 133 tested isolates, 64% belonged to MAT1–1 and 36% to MAT1–2. ...
... In Syria, out of the 133 tested isolates, 64% belonged to MAT1–1 and 36% to MAT1–2. Both MATs were found in six provinces but MAT-1–1 alone was found in three provinces (Omar et al. 2011). There is a dearth of information on this fungus, as similar studies have not been done on D. rabiei in Iran. ...
... In Syria, out of the 133 tested isolates, 64% were MAT1–1 and 36% were MAT1–2. Both MATs were found in six provinces, but MAT1–1 alone was found in three provinces (Omar et al. 2011). A single mating type of A. rabiei has been reported from several areas of the world including California, India and Australia (Kaiser 1997; Khan 1999; Taylor & Ford 2007). ...
Ascochyta blight, caused by Ascochyta rabiei is the most destructive disease of aerial parts of chickpea (Cicer arietinum L.) worldwide. Forty isolates of A. rabiei representing eight geographical regions, were collected from the west and south western Iran, and analysed for mating type distribution and fertility. A multiplex PCR assay using specific primers designed to amplify partial regions of the MAT1–1 and MAT1–2 idiomorphs was used to facilitate population analysis. Didymella rabiei populations were dominated by MAT1–1 mating type. The fertility status of isolates was determined using controlled crosses in vitro, pairing each isolate with compatible standard testers (USDA-AR-20 and USDA-AR21). Out of the 40 tested isolates, 38 isolates (95%) were MAT1–1 and two isolates (5%) were MAT1–2. Both mating types were present in Gachsaran and Jalian Populations, where Chi-square tests showed the proportions of each mating type were significantly different from 1:1 ratio. The predominance of one mating type in populations indicates that sexual reproduction is rare or may not occur with significant frequency in D. rabiei populations associated with chickpea in Iran. Microscopic studies of naturally infected tissues and inoculated with standard testers, which had been kept for two years under natural conditions, revealed the development of pseudothecia.
... Sexual reproduction is controlled by a single regulatory locus referred as mating-type locus and alternate sequences at the mating-type locus are completely dissimilar and code for different regulatory genes. The presence of opposite mating types (MAT1e1 and MAT1e2) and the teleomorph have been reported from most chickpea-growing regions in the world (Armstrong et al., 2001; Barve et al., 2003; Peever et al., 2004; Rhaiem et al., 2008; Vail and Banniza, 2009; Atik et al., 2011). The genetic structures of D. rabiei populations have been estimated using differential chickpea genotypes (Udupa et al., 1998; Vail and Banniza, 2008) and molecular markers (Peever et al., 2004; Varshney et al., 2009). ...
... Wild chickpea species (Cicer judaicum, Cicer bijugum and Cicer pinnatifidum) were also surveyed in their natural habitat, and wild accessions planted at Tartous research station for rejuvenation by the Genetic Resources Service of ICARDA were also surveyed. No wild chickpea plants were infected in their native habitat in both seasons, and only C. pinnatifidum was infected at Gammaseh Research Station in Tartous in the 2008e2009 season (Atik et al., 2011). Thus, all wild chickpea samples were collected from this species. ...
... Mycelium of each isolate was ground to a fine powder using a bead beater. DNA was extracted using a modified mini-preparation protocol using the cetyltrimethylammonium bromide (CTAB) method (Chongo et al., 2004; Vail and Banniza, 2009; Atik et al., 2011). The quantity and quality were assessed by running 1 ml of the DNA on 1% agarose gel, stained by ethidium bromide and photographed under UV illumination . ...
... Sexual reproduction is controlled by a single regulatory locus referred as mating-type locus and alternate sequences at the mating-type locus are completely dissimilar and code for different regulatory genes. The presence of opposite mating types (MAT1e1 and MAT1e2) and the teleomorph have been reported from most chickpea-growing regions in the world (Armstrong et al., 2001; Barve et al., 2003; Peever et al., 2004; Rhaiem et al., 2008; Vail and Banniza, 2009; Atik et al., 2011). The genetic structures of D. rabiei populations have been estimated using differential chickpea genotypes (Udupa et al., 1998; Vail and Banniza, 2008) and molecular markers (Peever et al., 2004; Varshney et al., 2009). ...
... Wild chickpea species (Cicer judaicum, Cicer bijugum and Cicer pinnatifidum) were also surveyed in their natural habitat, and wild accessions planted at Tartous research station for rejuvenation by the Genetic Resources Service of ICARDA were also surveyed. No wild chickpea plants were infected in their native habitat in both seasons, and only C. pinnatifidum was infected at Gammaseh Research Station in Tartous in the 2008e2009 season (Atik et al., 2011). Thus, all wild chickpea samples were collected from this species. ...
... Mycelium of each isolate was ground to a fine powder using a bead beater. DNA was extracted using a modified mini-preparation protocol using the cetyltrimethylammonium bromide (CTAB) method (Chongo et al., 2004; Vail and Banniza, 2009; Atik et al., 2011). The quantity and quality were assessed by running 1 ml of the DNA on 1% agarose gel, stained by ethidium bromide and photographed under UV illumination . ...
a b s t r a c t Simple sequence repeats and mating type markers were used to estimate the genetic diversity of 133 Didymella rabiei isolates collected from nine provinces of Syria. Moreover, phenotyping was done on 56 isolates randomly selected from the different genetic groups using five chickpea genotypes. The genetic diversity of D. rabiei population was high with inter-population variability accounting for 83% of the total variation, whereas the genetic diversity among populations was very low (17%). Principal component analysis grouped the isolates from Aleppo, Idlib, Hama, Homs and Hassakeh provinces together, while Daraa and Tartous were in different groups. Isolates from Lattakia and Suweida provinces formed very distinct clusters compared to the others. The 56 isolates were grouped into four pathotypes, namely, pathotype-1 (12 isolates), pathotype-2 (13 isolates), pathotype-3 (5 isolates) and pathotype-4 (26 iso-lates) with varying degrees of virulence on the chickpea genotypes. Our findings showed a clear genetic shift toward more virulence over time and space in the populations of D. rabiei in Syria. These results stress the need for chickpea breeding materials to be tested for resistance to the more virulent patho-types. Also, concerted action should be taken to ensure the shipment of healthy seeds of international chickpea nurseries to avoid D. rabiei genotypes or pathotypes flow from Syria to other countries.
... mM, DNA Taq polymerase-1 U, 2 µM of each primer. Cycling conditions consisted of an initial denaturation at 95 • C for 5 min followed by 35 cycles of 95 • C for 30 s, 60 • C for 30 s, 72 • C for 5 min, and a final extension at 72 • C for 5 min [23]. The PCR products were separated electrophoretically in 1.5% agarose gels, stained with ethidium bromide-400 µg/ml. ...
... During the sexual phase, new combinations of alleles are produced that may increase genetic diversity in pathogens and cause changes in their interaction with host plant [14]. High genetic diversity has been detected within populations from countries where both mating types exist [10,23,37]. In contrast, a very low genetic diversity was observed in Australia, where only one mating has been detected and the population is reproducing solely clonally [13][14][15][16][17][18][19]. ...
Ascochyta blight (Didymella rabiei) is an economically important disease of chickpea in Morocco and other parts of the world. Knowledge about pathogen diversity and their aggressiveness in the Moroccan D. rabiei population can help breeders to develop appropriate breeding strategies for the management of Ascochyta blight. The genetic diversity of 41 D. rabiei isolates collected from four major chickpea growing regions of Morocco and 40 isolates from Syria was estimated using nine polymorphic microsatellite markers. Multiplex MAT-specific PCR with three primers was used for mating types frequency analysis in the Moroccan populations. The aggressiveness of D. rabiei isolates was assessed using four chickpea differential genotypes and seven Moroccan Kabuli chickpea cultivars. The Moroccan D. rabiei population showed high genetic diversity (Ht=0.60) similar to many populations worldwide. The diversity was distributed within regions with no geographic preferences inside Morocco but with differentiation from the Syrian population. The high genetic diversity may be due to high gene flow among regions and/or to the presence of both mating types (MAT 1-1 and MAT 1-2), that can enhance the risk of sexual reproduction of D. rabiei. This genetic diversity could be responsible for the variation of Moroccan isolates in their aggressiveness on chickpea genotypes. Three pathotypes were identified, where the highly aggressive pathotype caused high disease severity on most of the released chickpea cultivars. This is the first report of pathogen diversity, mating types, and aggressiveness of D. rabiei population in Morocco. The information will be useful to breed chickpea cultivars resistant to pathotypes with high levels of aggressiveness to minimize the resistance breakdown of popular chickpea varieties.
... Breeding cultivars with durable resistance to AB is a challenging task because of the continuous evolution of the pathogen and the appearance of new virulent pathotypes (Atik et al. 2011;Imtiaz et al. 2011). This makes resistance short-lived and consequently limits the effectiveness of resistant cultivars. ...
... Reddy and Singh (1984) reported 11 Kabuli and 6 Desi genotypes resistant to AB. However, among (Atik et al. 2011;Imtiaz et al. 2011). Malhotra et al. (2003) reported the development of more than 3,000 lines with moderate AB resistance. ...
Chickpea is a grain legume with valuable nutritional characteristics. It is a basic aliment in Asian countries such as India and Pakistan as well as a traditional ingredient in Mediterranean diets. Biotic stresses such as ascochyta blight (AB) and fusarium wilt (Foc), together with other diseases, such as botrytis gray mold (BGM) and rust, are major constraints on stable chickpea production. Marker-assisted selection (MAS) is a tool that is significantly augmenting the efficacy and efficiency of chickpea breeding programs. This chapter reviews the current status and future potential of genomic tools for chickpea breeding aimed at countering biotic stresses. It also provides an overview of causal agents, host resistance inheritance, gene or quantitative trait locus (QTL) mapping, and genetic resources. An overview of the progress in introgression of resistance genes to cultivated chickpea as well as integrated disease management (IDM) is also provided.
... This is explained by the low temperature required for sexual stage formation which exists in the north of Iraq during the winter season (low temperature and relatively high humidity). Through the sexual recombination, new combinations of alleles occurre that may enhance genetic variation within the pathogen populations and lead to changes in their interaction with the host plant (Atik et al., 2011;McDonald & Linde, 2002). Adaptation of isolates to their host plant occurres more rapidly in sexually reproducing pathogens in the presence of both mating types, (Bar et al., 2021;McDonald & Linde, 2002). ...
Chickpea is considered as one of the most
important sources of proteins in many developing
countries including Iraq. Didymella rabiei, causing
ascochyta blight disease on chickpea, is a destructive
pathogen on chickpea in the north of the Iraq (Kurdistan
region). Detailed knowledge about the genetic
diversity and pathogenicity of the pathogens is necessary
to adopt appropriate disease control and management
strategies. For the purposes of this study, a combination
of phenotypic and genotypic characterizations
including simple sequence repeat (SSR) fingerprinting,
mating-types distribution and pathogenicity analyses
were used to assess a total of 145 D. rabiei isolates
collected from chickpea fields in the Sulaymaniyah
provincial region of northern Iraq in 2020. Our results
revealed a relatively high level of genetic diversity
(H = 0.66) within populations, with low differentiation
among populations. These findings together with mating
types which were found in a 50:50 ratio, suggest
the role of sexual reproduction in the fungus, primarily
as primary inoculums of D. rabiei which are likely
ascospores (sexual spores). On the contrary, the existence
of gene exchanges through either the movement
of infected seeds or plant debris is most probably the
main mechanism in reduction of differentiation among
populations. Hence, the use of certified chickpea seeds
and removing plant debris are recommended for effective
management of the disease
... Didymella rabiei (Kovachevski) von Arx [anamorf: Ascochyta rabiei (Passerini) Labrousse] affects all the above-ground parts of chickpea, but causes significant losses in seed yield and quality by causing breakage in the stem and capsule infections (Akem, 1999;Pande et al., 2005). If the environmental conditions are suitable, disease development increases and can cause yield losses up to 100% (Navas-Cortes et al., 1998;Vail and Banniza, 2009;Atik et al., 2011). ...
With the rapid increase in the world population, food accessibility and food safety problems are increasing day by day. There are some fungal disease factors that limit production and yield in chickpea cultivation, which has a high protein content, is easy to digest, and has wide adaptability. In order to determine this fungal flora especially seen during storage, a total of thirty-four different chickpea seed samples, eight of which were taken from the chickpeas stored in open stack form in the Merkez, Kâhta and Besni districts of Adıyaman province, in 2021 and twenty-six from the products of 2022, were examined. Identifications were made with morphological and microscopic techniques together with fungal isolations using Blotter and PDA method from these seeds. At the end of the study, the fungal flora content of Aspergillus spp. (42%), Rhizopus stolonifer (29%), Penicillium sp. (13%), Alternaria spp. (7%), Curvularia spp. (5%) and Trichoderma spp. (4%) was detected. In isolations made by PDA method, Aspergillus spp. (39%), Rhizopus stolonifer (35%), Penicillium sp. (12%), Trichoderma spp. (9%), Alternaria spp. (3%), Curvularia spp. (2%) was detected. These results obtained from Adıyaman province are guiding for additional studies to be carried out for the control of chickpea microflora.
... The presence of both mating types has been confirmed in Algeria, Argentina, Bulgaria, Canada, Egypt, Greece, Iran, Israel, Italy, Libya, Morocco, Pakistan, Portugal, Spain, Syria, Tunisia, Turkey, and the USA (Pacific Northwest), but their mating-type distribution frequency differs (Bencheqroun et al., 2022;Crociara et al., 2020;Kaiser & Küsmenoglu, 1997;Manjunatha et al., 2018). In some countries, the A. rabiei populations have a 1:1 ratio for the two mating types (Nourollahi et al., 2011;Peever et al., 2004), while others do not have an equal mating type ratio (Ali et al., 2012;Atik et al., 2011;Getaneh et al., 2021;Rhaiem et al., 2007Rhaiem et al., , 2008. ...
The necrotrophic fungus Ascochyta rabiei causes Ascochyta blight (AB) disease in chickpea. A. rabiei infects all aerial parts of the plant, which results in severe yield loss. At present, AB disease occurs in most chickpea-growing countries. Globally increased incidences of A. rabiei infection and the emergence of new aggressive isolates directed the interest of researchers toward understanding the evolution of pathogenic determinants in this fungus. In this review, we summarize the molecular and genetic studies of the pathogen along with approaches that are helping in combating the disease. Possible areas of future research are also suggested.
Taxonomy:
kingdom Mycota, phylum Ascomycota, class Dothideomycetes, subclass Coelomycetes, order Pleosporales, family Didymellaceae, genus Ascochyta, species rabiei.
Primary host:
A. rabiei survives primarily on Cicer species.
Disease symptoms:
A. rabiei infects aboveground parts of the plant including leaves, petioles, stems, pods, and seeds. The disease symptoms first appear as watersoaked lesions on the leaves and stems, which turn brown or dark brown. Early symptoms include small circular necrotic lesions visible on the leaves and oval brown lesions on the stem. At later stages of infection, the lesions may girdle the stem and the region above the girdle falls off. The disease severity increases at the reproductive stage and rounded lesions with concentric rings, due to asexual structures called pycnidia, appear on leaves, stems, and pods. The infected pod becomes blighted and often results in shrivelled and infected seeds.
Disease management strategies:
Crop failures may be avoided by judicious practices of integrated disease management based on the use of resistant or tolerant cultivars and growing chickpea in areas where conditions are least favourable for AB disease development. Use of healthy seeds free of A. rabiei, seed treatments with fungicides, and proper destruction of diseased stubbles can also reduce the fungal inoculum load. Crop rotation with nonhost crops is critical for controlling the disease. Planting moderately resistant cultivars and prudent application of fungicides is also a way to combat AB disease. However, the scarcity of AB-resistant accessions and the continuous evolution of the pathogen challenges the disease management process.
Useful websites:
https://www.ndsu.edu/pubweb/pulse-info/resourcespdf/Ascochyta%20blight%20of%20chickpea.pdf https://saskpulse.com/files/newsletters/180531_ascochyta_in_chickpeas-compressed.pdf http://www.pulseaus.com.au/growing-pulses/bmp/chickpea/ascochyta-blight http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/plant-diseases/grains-pulses-and-cereals/ascochyta-blight-of-chickpea http://www.croppro.com.au/crop_disease_manual/ch05s02.php https://www.northernpulse.com/uploads/resources/722/handout-chickpeaascochyta-nov13-2011.pdf http://oar.icrisat.org/184/1/24_2010_IB_no_82_Host_Plant https://www.crop.bayer.com.au/find-crop-solutions/by-pest/diseases/ascochyta-blight.
... The blight disease is of very grave concern in north western region of India and can cause complete yield losses in chickpea under severe epidemic (Nene and Reddy 1987). The presence of sexual and asexual stages of A. rabiei generates high degree of pathogenicity and genetic diversity in most blight epidemic regions (Atik et al. 2011;Rhaiem et al. 2008;Manjunatha et al. 2018). ...
The Ascochyta Blight (AB) caused by Ascochyta rabiei is recognized as a major foliar disease of chickpea worldwide. The rapid detection of AB is a prerequisite for the effective and timely management of disease at an early stage to prevent the AB epidemics in chickpea. The Indian isolates of A. rabiei were characterized pathogenically and sequencing of Internal Transcribed Spacer (ITS) region. The phylogenetic analysis of ITS sequences indicated 99.97% similarity index and isolates formed two major clusters through neighbour joining analysis. The RAPD monomorphic bands were cloned and sequenced. The best set of SCAR marker pairs designated as SCAR1F/SCAR1R were validated using PCR with sensitivity of 0.30 ng of genomic DNA. The RAPD derived SCAR marker demonstrated high sensitivity and were species specific in the detection of A. rabiei. The SCAR marker could be used for quick and timely detection of the A. rabiei fungus in seed materials of quarantine importance for phytosanitary certification of chickpea.
... D. rabiei affects all above ground parts of chickpea, where stem breakage and pod infection cause high losses in yield and quality of seeds (Akem 1999;Pande et al. 2005). Yield losses of up to 100% may be experienced under congenial environmental conditions for crop growth and disease development (Navas-Cortes et al. 1998;Vail and Banniza 2009;Atik et al. 2011). ...
Chickpea Ascochyta blight caused by Didymella rabiei is one of the most important fungal diseases affecting yield and seed quality negatively in Turkey. Breeding efforts against this devastating disease fail as the resistance/tolerance is broken in a short period of their commercial cultivation. This study was aimed to determine the status of Ascochyta blight epiphytotics and the effect of climatic factors on the disease incidence and severity in Turkey. Chickpea fields were surveyed for disease prevalence and severity in forty-five major chickpea-growing provinces in 9 climatic regions in the cropping season 2014, 2015, and 2016 in Turkey. The data on major weather parameters, i.e., rainfall (mm), air temperature (oC) and relative humidity (%), were procured from Ministry of Agriculture and Forestry, Turkey, and correlations among disease severity, altitude, weed density, nodule numbers, and climatic conditions were calculated. Principal component analysis was studied to determine the complex effects of all the variables on Ascochyta disease severity. It was observed that there was significant difference in percent incidence and severity of Ascochyta blight among the 45 provinces representing nine agro-climatic regions during the period under study. The highest disease incidence and severity (%) were recorded in Bosporus, Black Sea, Aegean and Mediterranean regions, while it was the lowest in Eastern Anatolia and Southeastern Anatolia. Negative correlation was recorded between disease severity and altitude and temperature, and that relative humidity (%) and rainfall (mm) showed statistically positive correlation with the disease severity. The disease severity was not effected by nodule numbers and weed density ratios.
... The Mating type of D. rabiei isolates exhibited 1:1 (Mat 1.1/Mat1.2) distribution in Turkey (X 2 = 0.87; P= 0.35; Table 6), however, there were differences among regions wherein both mating types existed in close proximity. These results suggested random sexual propagation of D. rabiei in Turkey as reported from nearby chickpea producing countries such as Syria, Lebanon, and Iran (Reddy and Sing, 1990;Atik et al., 2011). This result also may explain the diverse aggressiveness patterns of D. rabiei from chickpea producing areas of Turkey. ...
Chickpea (Cicer arietinum L.) is a traditional crop species in Turkey that is cultivated in almost every province providing prominent economic income. Turkey has an important resource for both Cicer spp diversity and their phytopathogens like ascohyta blight caused by Didymella rabiei (Kovachevski) von Arx wherein resistance/tolerance is broken every 4-5 years in cultivated chickpea cultivars. In order to breed resistant/tolerant varieties in chickpea against D. rabiei, detailed and up to date analyses on population characterization is needed. This study was undertaken to define current aggressiveness patterns, pathotype and mating type distribution of D. rabiei population in chickpea growing areas of Turkey. The D. rabiei isolates were assigned to 5 virulence groups in which existence of pathotype IV, a new and aggressive group, was defined for the first time from farmers' fields and research institutes exhibiting continuous arm race between plant and pathogen. The isolates in each pathotype group depicted statistically important difference (P≤ 0.05) in virulence levels on chickpea genotypes. The mating type distribution of 971 D. rabiei isolates was 1:1 for Mat 1.1 and Mat 1.2 isolates (X 2 = 0.87, P= 0.35) exhibiting random sexual reproduction. Overall, the data obtained revealed the unstable aggressiveness nature of D. rabiei population in Turkey, which, in turn, explains frequent resistance overcome in registered chickpea genotypes leading to epidemics.
... Chickpea yield losses caused by A. rabiei in favorable cool and humid climates in in Iran may reach up to 100% (Shokouhifar et al., 2003;Vail and Banniza, 2008;Younessi et al., 2004). A. rabiei have sexual and asexual fruiting bodies, therefore high degree of genetic diversity and pathogenicity has been reported in most epidemic regions for A. rabiei (Atik et al., 2011;Rhaiem et al., 2008;Sharma and Ghosh, 2016). Highly virulence diversity of A. rabiei with six physiological races in Syria and Lebanon (Reddy and Kabbabeh, 1985), 11 pathotypes in USA (Jan and Weise, 1991) and 14 pathotypes group in Canada (Chongo et al., 2004) has been reported. ...
Ascochyta blight caused by Ascochyta rabiei (Pass.) Lab. (Telomorph: Didymella rabiei) (Kov.) is one of the most important fungal diseases in chickpea worldwide. Knowledge about pathogen aggressiveness and identification resistance sources to different pathotypes is very useful for proper decisions in breeding programs. In this study, virulence of 32 A. rabiei isolates from different part of Iran were analyzed on seven chick-pea differentials and grouped into six races based on 0-9 rating scale and susceptibility/resistant pattern of chickpea differentials. The least and most frequent races were race V and race I, respectively. Race V and VI showed highly virulence on most of differential, while race I showed least aggressiveness. Resistance pattern of 165 chickpea genotypes also were tested against six different A. rabiei races. ANOVA analysis showed high significant difference for isolate, chickpea genotypes and their interactions. Overall chickpea × isolate (race) interactions, 259 resistance responses (disease severity ≤ 4) were identified. Resistance spectra of chickpea genotypes showed more resistance rate to race I (49.70%) and race III (35.15%), while there were no resistance genotypes to race VI. Cluster analysis based on disease severity rate, grouped chickpea genotypes into four distinct clusters. Interactions between isolates or races used in this study, showed the lack of a genotype with complete resistance. Our finding for virulence pattern of A. rabiei and newly identified resistance sources could be considerably important for integration of as-cochyta blight resistance genes into chickpea breeding programs and proper decision in future for germplasm conservation and diseases management.
... Rhaiem et al. (2007) analysed the idiomorph frequencies in 123 isolates of Ascochyta rabiei in Tunisia and found 99 isolates with idiomorph MAT1-1 (80%) and 24 with idiomorph MAT1-2 (20%), giving a 4:1 ratio. In Syria, Atik et al. (2011) analysed 133 isolates of A. rabiei and found 64% MAT1-1 and 36% MAT1-2 (ratio 2:1). Therefore, the distribution of frequencies of mating-type idiomorphs are probably not identical between different populations of the fungus, nor permanent; changes in P. fijiensis ratios in the field probably depend on regional environmental factors and selective pressure related to Musa cultural practices. ...
Pseudocercospora (previously known as Mycosphaerella) fijiensis causes black Sigatoka disease in banana (Musa spp.) and it is considered the most devastating pathogen of this crop worldwide. To improve the knowledge about its evolutionary patterns, we determine the genetic variability of populations from two regions: The Center Pacific (Colima and Michoacan) and the South of Mexico (Chiapas, Tabasco, and Oaxaca) using 10 Simple Sequence Repeat (SSR) loci and the MAT‐specific PCR assay. Both mating types were present in all regions under study, and their frequencies were 63% MAT1‐1 and 37% MAT1‐2. The SSR markers showed an average of three alleles per locus, resulting 34 alleles in total. The genetic diversity (HT) is 0.3308, but at local level (HS) ranges from 0.0976 (Colima) to 0.2228 (Oaxaca). However, the genotypic diversity is usually high (H’>2.4, S>0.89). The cluster analysis grouped isolates in five clusters with high statistical support (au>80%), suggesting a geographic organization of the genetic variability of P. fijiensis; AMOVA, the minimum spanning tree and the population structure analysis supported this result, and all data indicates that the major genetic differences are between the different populations under analysis. Thus, the high level of genetic variability in P. fijiensis is attributed partly to a high rate of sexual reproduction, and also to a strong evolutive capacity coupled with isolation due to the limited of genetic flow between distant populations, both possibilities could be playing a relevant role in population differentiation of the pathogen.
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... Sexual reproduction is controlled by a single regulatory locus referred to as a mating-type locus and alternate sequences at the mating-type locus are completely dissimilar and code for different regulatory genes. The presence of opposite mating types (MAT1-1 and MAT1-2) and the teleomorph have been reported from some chickpea-growing regions in the world [24][25][26][27][28][29]. The morphological characteristics of A. rabiei and Phoma medicaginis var. ...
Ascochyta blight (AB) caused by Ascochyta rabiei (Pass.) Labr. is an important and widespread disease of chickpea (Cicer arietinum L.) worldwide. The disease is particularly severe under cool and humid weather conditions. Breeding for host resistance is an efficient means to combat this disease. In this paper, attempts have been made to summarize the progress made in identifying resistance sources, genetics and breeding for resistance, and genetic variation among the pathogen population. The search for resistance to AB in chickpea germplasm, breeding lines and land races using various screening methods has been updated. Importance of the genotype × environment (GE) interaction in elucidating the aggressiveness among isolates from different locations and the identification of pathotypes and stable sources of resistance have also been discussed. Current and modern breeding programs for AB resistance based on crossing resistant/multiple resistant and high-yielding cultivars, stability of the breeding lines through multi-location testing and molecular marker-assisted selection method have been discussed. Gene pyramiding and the use of resistant genes present in wild relatives can be useful methods in the future. Identification of additional sources of resistance genes, good characterization of the host–pathogen system, and identification of molecular markers linked to resistance genes are suggested as the key areas for future study.
... Ascochyta blight caused by Ascochyta rabiei (Teleomorph: Didymella rabiei) is one of the major problems facing chickpea production worldwide and causes a huge loss of yield and quality -up to 100% in severely infected fields (Acikgoz et al., 1994). Seed treatment and foliar application of fungicides are often used for controlling this disease, but, unfortunately, they are still unsuccessful and uneconomical (Nene and Reddy, 1987;Atik et al., 2011). The use of resistant cultivars is considered the best option for long-term Ascochyta blight management. ...
A global collection of 43 chickpea (Cicer arietinum L.) genotypes, resistant and susceptible to Ascochyta blight caused by Ascochyta rabiei was evaluated for the disease under controlled conditions. In this study three known pathotypes (P-I, P-II, and P-III) were used to evaluate the reactions of this collection. The chickpea genotypes were also characterized using 14 microsatellite markers flanking the genomic regions associated with Ascochyta blight resistance quantitative trait loci (QTLs). Phenotyping results indicated that 27 genotypes were resistant to P-I, 14 to P-II, and five to P-III, revealing the possible erosion of resistance through the evolution of virulent pathogen pathotypes. The genetic diversity analysis revealed 67 alleles at 14 microsatellite loci with an average of 4.8 alleles per locus among the genotypes tested. Genetic similarity estimates differentiated four subclusters (A, B, C, and D) of the genotypes. However, none of sub-clusters were separated into resistant genotypes for a specific pathotype. The genetic diversity ranged from 0.48 to 0.80 which indicated that there is considerable variation in QTL regions associated with Ascochyta blight resistance among the collections of chickpea genotypes studied, as assessed using the hyper-variable microsatellite markers.
... However, there is a small probability that MAT1-1 does occur in Australia, albeit at very low frequencies. This is because chickpea seed sourced from overseas locations such as Canada and Syria could be infected with both mating types (Armstrong et al. 2001;Atik et al. 2011). Also the teleomorph was reported from chickpea stubble in Western Australia in 2003 (Galloway and MacLeod 2003). ...
The study examined the genetic structure and potential for adaption to host genotype of Ascochyta rabiei, a major necrotrophic fungal pathogen of chickpea. For this, A. rabiei populations derived from six major chickpea growing regions in Australia were characterized using 20 polymorphic microsatellite markers. The overall gene (H = 0.094) and genotypic (D = 0.80) diversities among the entire population were low, indicating the establishment of a recent founder population. Since, no significant genetic differentiation was detected among growing regions, subsequent anthropogenic dispersal was proposed, mainly through seed movement. The highest genotypic diversity and allelic richness was detected at Kingsford, South Australia, thought to be one of the sites of industry establishment in the 1970s and hence the centre of introduction. Despite assessing 206 isolates collected in 2010 from host genotypes with differential disease responses, no significant co-occurrence of fungal haplotype with host genotype was detected. Rather a single haplotype that accounted for 70 % of the total isolates assessed was detected on all host genotypes assessed and from all regions. Therefore, we propose that up until 2010, host reaction was not a major influence on the Australian A. rabiei population structure. Additionally, the detection of a single mating type only, MAT1-2 indicated asexual reproduction, further influencing low haplotype diversity and resulting in a population comprising of multiple clones with relatively few haplotypes compared to populations in other continents.
... Breeding for Ascochyta blight resistant cultivars has been attempted since the forties (Luthra et al. 1935), but progress has been limited, mainly due to lack of sufficient information on the genetics of resistance to the disease and the evolving nature of the pathogen (Atik et al. 2011, Imtiaz et al. 2011. The information on the resistance to the disease generated in the study of Malik et al. (2005), and subsequently other studies (Danehloueipour et al. 2007, Bhardwaj et al. 2010) indicated that there is sufficient genetic variation in chickpea which can be exploited to pyramid different sources of resistances. ...
Inheritance of resistance to race 4 of Ascochyta rabiei was studied in fifteen chickpea accessions known internationally for Ascochyta blight (AB) resistance. Resistance in ILC 200, ILC 5921, ILC 6043 and ILC 6090 was governed by a single recessive gene. Resistance in ILC 202 and ILC 2956 was conferred by two recessive complementary genes. In the case of ILC 5586, resistance was controlled by two dominant complementary genes and in the case of ILC 2506, two recessive genes with epistasis interaction were responsible for resistance. Resistance in ILC 3279, ILC 3856 and ILC 4421 was controlled either by three recessive genes or two recessives duplicated genes and in ILC 72, ILC 182 and ILC 187 resistance was polygenic in nature. The study provided insights into the genetics of Ascochyta blight resistance, and these could be used in crossing programmes to develop durable resistance. While the virulence spectrum of the pathogen in a region plays a crucial role in the deployment of resistance, ILC72, ILC182, ILC200, ILC442 and ILC6090 could provide acceptable level of resistance if incorporated into commercial cultivars.
... Breeding for Ascochyta blight resistant cultivars has been attempted since the last century (Luthra et al. 1935), but progress has been limited, mainly due to a lack of sufficient information on the genetics and molecular basis of resistance to the disease Atik et al. 2011). Ascochyta blight resistance is a complex character usually considered a quantitative trait. ...
Physical and genetic maps of chickpea a
QTL related to Ascochyta blight resistance and
located in LG2 (QTLAR3) have been constructed.
Single-copy markers based on candidate genes located
in the Ca2 pseudomolecule were for the first time
obtained and found to be useful for refining the QTL
position. The location of the QTLAR3 peak was linked
to an ethylene insensitive 3-like gene (Ein3). The Ein3
gene explained the highest percentage of the total
phenotypic variation for resistance to blight (44.3 %)
with a confidence interval of 16.3 cM. This genomic
region was predicted to be at the Ca2 physical position
32–33 Mb, comprising 42 genes. Candidate genes
located in this region include Ein3, Avr9/Cf9 and
Argonaute 4, directly involved in disease resistance
mechanisms. However, there are other genes outside
the confidence interval that may play a role in the
blight resistance pathway. The information reported in
this paper will facilitate the development of functional
markers to be used in the screening of germplasm
collections or breeding materials, improving the
efficiency and effectiveness of conventional breeding
methods.
... The overall distribution showed significant deviation from 1:1 ratio. However, Chi-square tests of the subsamples from six provinces showed they were not significantly different from 1:1 distribution (Atik et al., 2011). MAT1-2 has been reported as dominant in Turkey and (MAT1-1) in Tunisia (Taylor and Ford, 2007;Rhaiem et al., 2007). ...
... The primary sources of inoculum for Ascochyta infections on the moderately resistant chickpea cultivar (Ghab-4) could be from the plots where chickpea straw was left from the previous seasons. The oversummering chickpea straw in ZT could also be a breeding ground for D. rabiei since the two mating types (MAT1-1 and MAT1-2) exist in Syria (Omar et al., 2011). From the sexual reproduction, ascospores will be released in early spring and initiate disease foci in neighboring fields. ...
Field investigations were carried out during rabi (October–March), 2020–21 and 2021–22 in major chickpea-growing areas of Banda, Mahoba, Hamirpur and Chitrakoot districts of Bundelkhand region of Uttar Pradesh, India to find out a suitable management strategy for ascochyta blight disease in standing crop conditions. A survey study was carried out during January–February, 2022 to find out the occurrence of ascochyta blight. The overall severity of ascochyta blight observed in four surveyed districts ranged between 15.82–17.50%. The pathogen exhibited floccose and white to pale olive colored colony with irregular white periphery on potato dextrose agar media after 14 days of incubation. Maximum growth (46.2 mm) of mycelia was recorded on oatmeal agar media followed by the growth of 43.2 and 40.4 mm obtained in malt extract agar media and potato dextrose agar media, respectively. In standing crop conditions, two sprays of combination of Tebuconazole 50%+Trifloxystrobin 25% WG @ 0.1% gave the maximum reduction in disease incidence (47.05%) and disease severity (63.86%) along with the highest enhancement in grain yield (54.81%), number of pods plant-1 (55.56%) and 100 grain weight (62.28%). Results revealed that ascochyta blight of chickpea was prevalent in Bundelkhand region of Uttar Pradesh. Oatmeal agar medium can be used for cultivation of Ascochyta rabiei. In field, ascochyta blight can be managed by two sprays of combination of Tebuconazole 50% + Trifloxystrobin 25% WG @ 500 g ha-1 at symptoms initiation and after 15 days of first spray.
The Ascochyta Blight (AB) caused by Ascochyta rabiei is recognized as a major foliar disease of chickpea worldwide. The rapid detection of AB is a prerequisite for the effective and timely management of disease at an early stage to prevent the AB epidemics in chickpea. The Indian isolates of A. rabiei were characterized pathogenically and sequencing of Internal Transcribed Spacer (ITS) region. The phylogenetic analysis of ITS sequences indicated 99.97% similarity index and isolates formed two major clusters through neighbour joining analysis. The RAPD monomorphic bands were cloned and sequenced. The best set of SCAR marker pairs designated as SCAR1F/SCAR1R were validated using PCR with sensitivity of 0.30 ng of genomic DNA. The RAPD derived SCAR marker demonstrated high sensitivity and were species specific in the detection of A. rabiei. The SCAR marker could be used for quick and timely detection of the A. rabiei fungus in seed materials of quarantine importance for phytosanitary certification of chickpea.
The pathotypes of Ascochyta rabiei, which caused Ascochyta blight, showed a high pathogenic variation. Forty-four chickpeas, including 26 cultivars commonly cultivated in Turkey and 18 global genotypes, were characterized for resistance status to Ascochyta blight, following inoculation with four pathotypes of A. rabiei. The pathogenicity experiments were conducted using the whole-plant inoculation method and completely randomized designs with three replicates. The pathogenicity tests revealed that 32, 17, 3, and 1 chickpea showed resistance reactions to pathotypes I, II, III, and IV, respectively. These chickpeas were genotyped with STMS (GAA47, TA146, and TA194), SCAR (SCK13603, SCAE19336, and SCY17590), and an allele specific (CaETR) MAS markers closely linked to QTLs located on linkage group 2 and 4 for Ascochyta blight resistance. QTLAR1 predicted blight resistance to pathotype I, with a rate of 65.9%. Strong correlations at P < 0.01 were found between resistance reactions of chickpeas to pathotype II and QTLAR2, which possible to predict the resistance in 79.55-81.82% of studied chickpeas. A significant association was found between QTLAR3 and resistance to pathotypes III and IV, which the most aggressive groups among A. rabiei isolates. Three chickpea genotypes (ICC 3996, ICC 12004, and ICC 4475) showed a high level of resistance to pathotypes I, II, and III. ICC 3996 was the only genotype for resistance to pathotype IV. This study is the most comprehensive phenotypic study to determine the resistance status of chickpeas against pathotype IV, and the first study showing a significant association between a MAS marker linked to QTLAR3 and blight resistance to pathotype III and IV. Breeders should include the isolates in pathotypes III and IV groups into pathogenicity tests due to the increase in their prevalence. The markers linked to QTLs determining the resistance to these pathotypes should be emphasized, and the efficiency of the use of these markers in breeding programs should be increased.
Chickpea ( Cicer arietinum L.) is one of the most important pulse crops in Ethiopia. Earlier reports and field observations have shown that Ascochyta blight caused by Ascochyta rabiei is one of the most devastating diseases of this crop in Ethiopia. Survey was conducted during August 2015 to February 2016 to determine the status of the blight disease in major chickpea the growing area of Ethiopia. A total of 251 on-station and on-farm fields were surveyed. Ascochyta blight was observed in 30 of the 251 fields and incidence ranged from 0 to 45.6 % with mean of El nino conditions.
Ascochyta blight, caused by Ascochyta rabiei (Pass.) Labr., is the most important foliar disease of chickpea (Cicer arietinum L.) in many countries. Many studies have been carried out on basis of population biology and host-plant resistance of A. rabiei, but the effect of endogenous plant hormone levels on resistance to ascochyta blight of chickpea has been studied rarely. Therefore, the study was designed to compare endogenous plant hormone levels in ascochyta blight susceptible and resistant chickpea genotypes under ascochyta blight infected conditions. ILC 263, (susceptible to ascochyta blight), FLIP 95-60C and FLIP 98-224C (resistant to ascochyta blight) were used to determine the level of plant hormones; indole-3-acetic acid (IAA), zeatin, gibberellic acid 3 (GA3), and abscisic acid (ABA). Concentrations of IAA, zeatin, GA3 and ABA were markedly increased in pods of resistant genotypes, FLIP 95-60C and FLIP 98-224C. It was suggested that high zeatin and GA 3 concentrations in pods could be detected as biochemical markers to determine resistance to ascochyta blight of chickpea genotypes since the genotypic effect was statistically significant only for zeatin and GA 3. Considering the statistically significant genotypic effects only for zeatin and GA3, these hormones may be used as biochemical markers to determine resistance to ascochyta blight of chickpea genotypes.
Ascochyta blight caused by the fungus Ascochyta rabiei
(AR) depresses chickpea production in Pakistan
and worldwide. Thirty two AR isolates representing six
geographical regions of Pakistan were compared with a
US-AR population for mating type frequency and genetic
variation. Mating type results showed that the Pakistani
AR (PAR) population had an apparent skewed (3
Mat1-2: 1 Mat1-1) distribution, although Chi-square
tests showed non-significant deviation from equal distribution
due to small sample sizes. The US population
showed a 1:1 distribution of the two mating types. The
uneven distribution of mating types indicates that sexual
reproduction among the PAR is rare due to either unavailability
of both mating types or lack of conducive
environment, but statistical analysis showed that panmixia
is there reflecting past recombinational events.
Genetic variation at six microsatellite loci was assessed
and each isolate was assigned to a microsatellite haplotype.
Population structure of the isolates was inferred
using Bayesian analyses implemented in the structure
software which differentiated isolates into three distinct
clusters, two clusters of PAR and one of the US isolates.
However, few isolates from the US shared the same genetic
background with one cluster of the PAR isolates,
providing a link of inter-continental migration of the
pathogen. Additionally, the two clusters of PAR-isolates
are not strictly associated with geographic locations in
Pakistan, suggesting frequent gene flow of AR among
different locations. Future studies should extend the
sampling of representative populations to overcome the
limitations of the small sample size for more accurate assessment
of population structure.
Ascochyta blight (Didymella rabiei) is an economically important disease on chickpea in Syria and other parts of the world. Studies were conducted under plastic-house and field conditions to determine the effects of mixed infection of D. rabiei pathotypes on disease development on different chickpea genotypes. The plastic-house results showed that under mixed-genotype infections, disease severity caused by two-genotype mixtures (1+2, 1+3, 1+4, 2+3, 3+4) was not significantly different from the average level of disease caused by the most virulent pathotype in each mixture. Co-infection by Pathotypes-1+2, resulted in higher disease severity comparing with Pathotype-2 alone. Co-infection by the four Pathotypes mixture, resulted in lower disease severity comparing with Pathotype-4 alone. ILC-194 was the most susceptible genotype, followed by Ghab-1, while ICC-12004 was the most resistant genotype. In field experiments, all disease parameters and percent yield reduction were higher when chickpea genotypes were infected with a mixture of Pathotype-1 and 2 compared with individual inoculations with the two pathotypes. Chickpea variety mixture did not reduce parameters of disease epidemics. To develop disease epidemics under field conditions, it is better to mix Pathotype-1 and 2 compared with individual inoculations. Further studies are required to learn how pathotype mixtures affect disease epidemics in chickpea-Ascochyta pathosystem.
Keywords: Chickpea, Ascochyta blight, Didymella rabiei, Competition, Mixed-pathotypes.
Assessment of variability of Ascochyta rabiei (teleomorph: Didymella rabiei) was based on virulence tests of 40 isolates and on random amplified polymorphic DNA (RAPD) analysis of 39 isolates from Canada. In addition, isolates of A. rabiei from other countries were assessed in the virulence (18 isolates) and RAPD (20 isolates) analyses. Seven isolates of A. lentis (teleomorph: Didymella lentis) and two of A. pinodes (teleomorph: Mycosphaerella pinodes) also were included in the RAPD analysis. Significant line-isolate interactions in the virulence tests indicated that certain isolates were virulent only on certain lines. Canadian isolates were grouped into 14 pathotypes using eight chickpea differentials. These groupings also encompassed 17 of the 18 isolates from other countries. RAPD analysis of all 68 isolates using 8 primers produced 112 fragments, of which 96% were polymorphic. Similarities among A. rabiei isolates from Canada ranged from 20 to 100%. In the RAPD dendrogram, all five A. rabiei isolates from Australia, three of six from Syria, three of five from the United States, and one of two from India clustered within the major groups of Canadian isolates. There was a weak association between RAPD and pathotype groups. A. rabiei was 45% similar to A. lentis and only 14% similar to A. pinodes. The levels of DNA variability and virulence among isolates show that the population of A. rabiei in Canada is highly diverse.
SUMMARY Genetic diversity among 64 isolates of Ascochyta ra- biei obtained from diseased chickpea plants in 18 differ- ent provinces of Turkey was characterized by mi- crosatellite-primed PCR using di-, tri- and tetra-nu- cleotide repeats. Of sixteen primers tested, ten ampli- fied 61 bands, of which 56 were polymorphic. UPGMA (Unweighted Pair Group Method with Arithmetic Aver- age) analysis, performed with the resulting data of SSR (Simple Sequence Repeats) fingerprints clustered Turk- ish isolates of A. rabiei into seven groups. However, these groups did not correspond to their geographic origin. Group 2, the largest group consisting of 35 iso- lates from 16 different provinces, clustered together with one Syrian isolate belonging to pathotype 3 while isolates belonging to pathotypes 1 and 2 did not cluster with any isolate originating from Turkey. The highest genetic diversity within geographical populations was found in the South Eastern Anatolia region (Shannon index: 0.156). Also, rDNA ITS (Internal transcribed spacer) regions of isolates representative of each group were sequenced. The ITS1-5.8S-ITS2 sequences were highly conserved among all groups of A. rabiei. This is the first report on detection of genetic diversity in A. ra- biei populations in Turkey. The SSR fingerprints (three or four repeats) generated using A. rabiei DNA indicat- ed that such microsatellites are useful for population studies in this fungus.
Ascochyta blight ( AB), caused by Ascochyta rabiei is a major disease of chickpea ( Cicer arietinum L.), especially in areas where cool, cloudy, and humid weather persists during the crop season. Several epidemics of AB causing complete yield loss have been reported. The fungus mainly survives between seasons through infected seed and in infected crop debris. Despite extensive pathological and molecular studies, the nature and extent of pathogenic variability in A. rabiei have not been clearly established. Accumulation of phenols, phytoalexins ( medicarpin and maackiain), and hydrolytic enzymes has been associated with host-plant resistance (HPR). Seed treatment and foliar application of fungicides are commonly recommended for AB management, but further information on biology and survival of A. rabiei is needed to devise more effective management strategies. Recent studies on inheritance of AB resistance indicate that several quantitative trait loci (QTLs) control resistance. In this paper we review the biology of A. rabiei, HPR, and management options, with an emphasis on future research priorities.
Chickpea (Cicer arietinum L.) acreage has increased rapidly in western Canada since 1995, and Ascochyta rabiei (Pass.) Labr. is the most important pathogen of this new crop. Wind-borne ascospores produced by the teleomorph play an important role in disease spread and pathogen survival in many regions. The teleomorph stage, however, has not been reported in Canada. Mating-type assessments of 42 isolates from 34 fields in Saskatchewan were conducted using tester isolates. The two mating types occurred at similar frequencies across the region. Over-wintered chickpea residue was collected in April of 1999 and 2000. The teleomorph was detected on the residue by microscopic dissection and by two methods of ascospore discharge, one using a novel and inexpensive apparatus. Mature ascospores were found at six of seven sites in 1999. No ascospores were found in material from 13 sites in 2000. However, asci were found later in the season in a separate study conducted at one site. The occurrence of the teleomorph stage in the region may increase field-to-field spread of ascochyta blight of chickpea and contribute to increased genetic variability of the pathogen in western Canada.
The poor definition of variation in the ascochyta blight fungus (Ascochyta rabiei) has historically hindered breeding for resistance to the chickpea (Cicer arietinum L.) blight disease in West Asia and North Africa. We have employed 14 RAPD markers and an oligonucleotide probe complementary
to the microsatellite sequence (GATA)4 to construct a genotype-specific DNA fragment profile from periodically sampled Syrian field isolates of this fungus. By
using conventional pathogenicity tests and genome analysis with RAPD and microsatellite markers, we demonstrated that the
DNA markers distinguish variability within and among the major pathotypes of A. rabiei and resolved each pathotypes into several genotypes. The genetic diversity estimate based on DNA marker analysis within pathotypes
was highest for the least-aggressive pathotype (pathotype I), followed by the aggressive (pathotype II) and the most-aggressive
pathotype (pathotype III). The pair-wise genetic distance estimated for all the isolates varied from 0.00 to 0.39, indicating
a range from a clonal to a diverse relationship. On the basis of genome analysis, and information on the spatial and temporal
distribution of the pathogen, a general picture of A. rabiei evolution in Syria is proposed.
The incidence and severity of Ascochyta blight in potted chickpea trap plants exposed for 1-wk periods near infested chickpea debris in Crdoba, Spain, or in chickpea trap crops at least 100 m from infested chickpea debris in several locations in southern Spain were correlated with pseudothecial maturity and ascospore production ofDidymella rabiei from nearby chickpea debris. The period of ascospore availability varied from January to May and depended on rain and maturity of pseudothecia. The airborne concentration of ascospores ofD. rabiei was also monitored in 1988. Ascospores were trapped mostly from the beginning of January to late February; this period coincided with that of maturity of pseudothecia on the chickpea debris. Most ascospores were trapped on rainy days during daylight and 70% were trapped between 12.00 and 18.00 h. Autumn-winter sowings of chickpea were exposed longer to ascospore inoculum than the more traditional spring sowings because the autumn-winter sowings were exposed to the entire period of ascospore production on infested chickpea debris lying on the soil surface.
Eleven pathotype groups (A-K), including five not previously reported, ofDidymella rabiei (anamorphAscochyta rabiei), representing isolates of the pathogen from Ascochyta blight-affected chickpeas mainly from India, Pakistan, Spain and the
USA, were characterized using 44 single-spore isolates tested against seven differential chickpea lines. Of 48 isolates tested
for mating type, 58% belonged to MAT 1-1 and 42% to MAT 1-2. Thirty-nineD. rabiei isolates, as well as two isolates ofAscochyta pisi and six isolates of unrelated fungi, were analyzed using Randomly Amplified Polymorphic DNAs (RAPDs) employing five primers
(P2 at 40°C, and OPA3, OPC1, OPC11 and OPC20 at 35°C). Computer cluster analysis (UPGMA / NTSYS-PC) detected a relatively
low level of polymorphism among all theD. rabiei isolates, although atca 7% dissimilarity,ca 10 RAPD groups [I-X] were demarcated, as well as subclustering within the larger groups. By the same criteria, the maximum
dissimilarity for the whole population ofD. rabiei isolates wasca 13%. No correlation was found between different RAPD groups, pathotype, or mating type ofD. rabiei, although some evidence of clustering based on geographic origin was detected. The use of RAPDs enabled us to identify specific
DNA fragments that may have a potential use as genetic markers in sexual crosses, but none which could be used as virulence
markers.
Five Mycosphaerella graminicola populations from four geographic regions (Australia, Israel, Switzerland, and the USA) were assayed for neutral RFLP markers and mating type idiomorphs. On average, 25-30 genetically distinct isolates were selected from each population and their pathogenicity was measured on two wheat cultivars in a common garden experiment conducted in a greenhouse. A significant difference in pathogenicity was found between MAT1-1 and MAT1-2 isolates. On average, MAT1-1 isolates had 14-22% greater pathogenicity than MAT1-2 isolates. The pattern of higher pathogenicity in MAT1-1 isolates was consistent across four geographical populations and on two wheat cultivars. A uniform and continuous variation in pathogenicity was found among isolates within each mating type, but no genetic differentiation in selectively neutral RFLP loci was found between mating types, consistent with the hypothesis that differences in pathogenicity were not due to the effects of specific pathogenicity genes or non-random genetic backgrounds.
Ascochyta blights of chickpea, faba bean, and lentil are caused by Ascochyta rabiei, A. fabae, and A. fabae f. sp. lentis, respectively, all of which are important seedborne pathogens. Infected seed is important in the long-distance spread and survival of these pathogens. In the last 20-25 years, there has been a steady increase in the exchange of germplasm of cool season food legumes between countries. Seed transmission has been responsible for the introduction of the ascochyta blight pathogens of chickpea, faba bean, and lentil into, and for dissemination within, many countries worldwide. The teleomorphic (sexual) states of the blight pathogens of chickpea, faba bean, and lentil belong to the genus Didymella. These fungi are heterothallic, requiring the pairing of two compatible mating types for successful sexual reproduction. Movement of infected seed of these three crops not only leads to the introduction of virulent pathotypes, but may lead to the distribution of compatible mating types, thus allowing the development of the teleomorph in nature. Storage of chickpea, faba bean, and lentil seed at temperatures of 4° to -18°C in germplasm repositories not only prolongs the longevity of the seed but also of the associated seedborne ascochyta pathogens.
Ascochyta blight [Ascochyta rabiei (Pass.) Lab.] is the most destructive disease of chickpea (Cicer arietinum L.), but it can be managed effectively by the use of resistant cultivars. Therefore, a breeding programme was initiated during 1977-78 at ICARDA, Syria, to breed blight-resistant, high-yielding chickpeas with other desirable agronomic traits. Crosses were made in main season at Tel Hadya, Syria, and the F1s were grown in the off season at Terbol, Lebanon. The F2, F4 and F5 generations were grown in a blight nursery in the main season where blight epidemic was artificially created. The plants and progenies were scored for blight resistance and other traits. The F3 and F6 generations were grown in the off season under normal day length to eliminate late-maturing plants. The pedigree method of breeding was followed initially, but was later replaced by the F4-derived family method. The yield assessment began with F7 lines, first at ICARDA sites and later internationally. A total of 1584 ascochyta blight-resistant chickpea lines were developed with a range of maturity, plant height, and seed size not previously available to growers in the blight-endemic areas in the Mediterranean region. These included 92 lines resistant to six races of the ascochyta pathogen, and 15 large-seeded and 28 early maturity lines. New cultivars produced 33% more seed yield than the original resistant sources. The yield of chickpea declined by 340 kg ha(-1), with an increase in blight severity by one class on a 1-9 scale, reaching zero yield with the 8 and 9 classes. Development of blight-resistant lines made the introduction of winter sowing possible in the Mediterranean region with the prospect of doubling chickpea production. Twenty three cultivars have been released so far in 11 countries.
In July 2005, small (2 to 5 mm), elongated, dark brown spots on the stems of Cicer pinnatifidum Jaub. & Spach. were observed on plants grown in the rocky hills of the Kahramanmaras Province. To understand this phenomenon, field trips to Kahramanmaras, Adiyaman, and Sanliurfa provinces were conducted in the summer of 2006. C. pinnatifidum plants exhibiting symptoms similar to Ascochyta rabiei (Pass.) Lab. were collected during May and June. The plants had flowers and pods with seeds at the time of collection. Ascochyta blight symptoms on stems were not extensive. None of the plants had leaf symptoms, but one plant had lesions on its pods. Twelve plants exhibiting Ascochyta blight symptoms were taken to the laboratory, and necrotic parts were used for isolation of the fungi on potato dextrose agar (PDA). After 3 to 5 days of culturing on PDA, characteristic beige-to-dark brown colony development of A. rabiei from explants was observed and five isolates from different locations were recovered. The fungal colony growth was slow and limited conidia formed on PDA. The isolates were also cultured on chickpea meal agar (CMA) and Czapek Dox Agar (CDA) media. Abundant conidia formation occurred only on CMA, 10 to 12 days after culturing. Conidia were one-celled similar to that of A. rabiei of chickpea and single-spore isolations were done. C. pinnatifidum and chickpea cv. Gokce (C. arietinum L.) were inoculated with spore suspensions of 5 × 10 ⁵ spores per ml (2). Ten- to twelve-day-old seedlings were used for inoculation in the experiments. Brown-black lesions at the crown region on C. pinnatifidum seedlings were observed 9 to 10 days after inoculation, and characteristic Ascochyta blight symptoms on stems developed on chickpea cv. Gokce. The fungus was reisolated from the infected seedlings. For molecular characterization, mating type of the isolates was determined by PCR using A. rabiei specific Tail1, Com1, and Sp21 primers (1). A single band of Mat 1.2 specific 500- bp product was amplified by PCR from five of the A. rabiei isolates of C. pinnatifidum. This confirmed that the isolates from C. pinnatifidum are A. rabiei.
References: (1) M. P. Barve et al. Fungal Genet. Biol. 39:151, 2003. (2) M. S. A. Khan et al. Plant Pathol. 48:230, 1999.
Ascochyta blight (Didymella rabiei (Kovach) v. Arx) is an important disease of chickpea (Cicer arietinum L.) in most of the chickpea-growing countries of South Asia, the Middle East, the Mediterranean region and North Africa. It is especially important in countries that have adopted the winter-sown chickpea technology, where winter conditions that favour the growth of the crop are also ideal for the development of disease epidemics. Research has been carried out on the disease and the pathogen since it was first described on chickpea in 1911. These studies have centred on the pathogen, its biology, survival, spread and control. There are indications that the teleomorph of the pathogen may be playing a role in its variability and long distance spread. There are conflicting reports on the role ofinfected seed and debris in the survival and spread of the pathogen. Studies on strategies for control have focused largely on host resistance, but durable sources of resistance have not so far been identified. Emphasis is being shifted to integrated management of the disease. Despite the volume of research on ascochyta blight, some gaps still exist in our knowledge of the disease, especially in the areas of its spread, regional distribution and importance, epidemiology, mechanisms of pathogenic variability and genetics of host plant resistance.
Molecular variability of populations of Ascochyta rabiei from Saskatchewan collected in 1998 and 2002, and mating-type frequency of isolates from 1998, 2001 and 2002 were assessed. To evaluate the genetic diversity of different A. rabiei populations, 30 isolates from 1998 and 30 isolates from 2002 were compared by random amplified polymorphic DNA fingerprinting. Cluster analysis and analysis of molecular variance suggested differentiation of the 1998 and 2002 populations, yet equal amplicon diversity between populations with the majority of the variation occurring within each population was observed. Analysis of mating-type frequencies on 30 isolates each from 1998, 2001 and 2002 populations did not significantly depart from a 1 : 1 ratio suggesting random mating of each population. However, when 121 isolates from 2002 were analysed for mating type, a significant departure from a 1 : 1 ratio was found suggesting smaller sampling sizes for mating-type frequenciesmay not reveal true differences. In further support of the hypothesis of a randomly mating population in 1998, the Index of Association was not significantly different from zero. However, this measure suggested departure from panamixa in the 2002 population consistent with the skewed mating-type ratio. It was concluded that there was some evidence for genetic shift in populations of A. rabiei between 1998 and 2002, which is consistent with a shift in aggressiveness observed between these populations.
The population structure of Ascochyta rabiei (teleomorph: Didymella rabiei) in Tunisia was estimated among five populations sampled from the main chickpea growing regions using simple sequence repeat markers (SSR) and a mating type (MAT) marker. Mating type 2 isolates (MAT1-2) had reduced genetic and genotypic diversity relative to mating type 1 isolates (MAT1-1). This result, coupled with previous observations of lower overall frequency and restricted geographical distribution of MAT1-2 in Tunisia, and recent (2001) observation of the sexual stage, support the hypothesis of a recent introduction of MAT1-2. Despite the presence of both mating types in Nabeul, Kef and Jendouba, the hypothesis of random mating was rejected in these locations with multilocus gametic disequilibrium tests. Highly significant genetic differentiation (θ = 0·32, GST = 0·28, P < 0·001) was detected among populations and genetic distance and cluster analyses based on pooled allele frequencies revealed that populations from Nabeul and Kef were distinct from those in Beja, Bizerte and Jendouba. More than 70% of total gene diversity (HT = 0·55) detected was attributable to variation within populations compared to 28% among populations. This result, coupled with the occurrence of private alleles in each population, suggests that gene flow is currently limited among populations, even those separated by short geographic distances. The presence of two main genetic clusters was confirmed using Bayesian model-based population structure analyses of multilocus genotypes (MLGs) without regard to geographic origin of samples. The presence of MAT1-2 isolates in both clusters suggests at least two independent introductions of MAT1-2 into Tunisia that are likely to be the result of importation and planting of infected chickpea seeds.
SUMMARY A genome linkage map was developed for Ascochyta rabiei (Pass.) Labrousse, (teleomorph) Didymella rabiei (Kovachevski), an important pathogen causing ascochyta blight in chickpea (Cicer arietinum L.). The map was constructed using 96 progeny generated from a single pseudothecium produced from a cross between a USA MAT-2 isolate and an Australian MAT-1 isolate. The map comprised 126 molecular markers of which 69 were random amplified polymorphic DNA (RAPD) markers, 46 were amplified fragment length polymorphic (AFLP) markers, 10 were sequence-tagged microsatellite site (STMS) markers, and one was a sequence characterized amplified region (SCAR) marker. Eighteen large and 10 small linkage groups (LG) were characterized and the mating-type locus was mapped on to LGd. The map spanned 1271 cM with an average spacing between markers of 15.1 cM. The SCAR marker, specific for mating type 2, was designed to amplify a region of the MAT locus and was used to identify the mating type of A. rabiei isolates. One AFLP marker, derived from the MAT-1 parent, was closely linked to the mating-type locus (9.6 cM). The linkage map provides a framework for the future identification of the locations of other important traits such as virulence/avirulence and fungicide resistance. Findings from this study suggest that the MAT-2 isolates of D. rabiei should be renamed to MAT-1 isolates because the alpha-box, specific for MAT-1 from other ascomycetes, was amplified from A. rabiei MAT-2 isolates.
Forty-eight chickpea germplasm lines, including 22 differentials used in previous studies, were characterized for disease phenotypes following inoculation with six isolates of Didymella (anamorph Ascochyta) rabiei, representing a wide spectrum of pathogenic variation. Representative isolates were also directly compared with six previously identified races on eight chickpea genotypes. Many of the chickpea differentials reacted similarly to inoculation with each isolate of D. rabiei, and several previously identified races caused similar levels of disease on the differentials. This indicates that the number of differentials can be reduced significantly without sacrificing accuracy in describing pathogenic variation of D. rabiei on chickpea. Pathogenic variation among samples of US isolates allowed classification of the isolates into two pathotypes. The distribution of disease phenotypes of the 48 germplasm lines was bimodal after inoculation with pathotype I isolates, whereas the distribution of disease phenotypes was continuous after inoculation with pathotype II isolates. Such distinct distribution patterns suggest that chickpea plants employ different resistance mechanisms to each pathotype and that the two pathotypes may have different genetic mechanisms controlling pathogenicity. The advantages of using the two-pathotype system in assaying pathogenicity of the pathogen and in studying resistance mechanisms of the host are discussed. Three chickpea accessions, PI 559361, PI 559363 and W6 22589, showed a high level of resistance to both pathotypes, and can be employed as resistance sources in chickpea breeding programmes for resistance to ascochyta blight.
The progress made in the molecular characterization of the mating types in several filamentous ascomycetes has allowed us to better understand their role in sexual development and has brought to light interesting biological problems. The mating types of Neurospora crassa, Podospora anserina, and Cochliobolus heterostrophus consist of unrelated and unique sequences containing one or several genes with multiple functions, related to sexuality or not, such as vegetative incompatibility in N. crassa. The presence of putative DNA binding domains in the proteins encoded by the mating-type (mat) genes suggests that they may be transcriptional factors. The mat genes play a role in cell-cell recognition at fertilization, probably by activating the genes responsible for the hormonal signal whose occurrence was previously demonstrated by physiological experiments. They also control recognition between nuclei at a later stage, when reproductive nuclei of each mating type which have divided in the common cytoplasm pair within the ascogenous hyphae. How self is distinguished from nonself at the nuclear level is not known. The finding that homothallic species, able to mate in the absence of a partner, contain both mating types in the same haploid genome has raised more issues than it has resolved. The instability of the mating type, in particular in Sclerotinia trifolorium and Botrytinia fuckeliana, is also unexplained. This diversity of mating systems, still more apparent if the yeasts and the basidiomycetes are taken into account, clearly shows that no single species can serve as a universal mating-type model.
Degenerate primers designed to correspond to conserved regions of the high mobility group (HMG) protein encoded by the MAT1-2 gene of Cochliobolus heterostrophus, Cochliobolus sativus, and Alternaria alternata were used to amplify the portion of the sequence corresponding to the HMG box motif from Ascochyta rabiei (teleomorph: Didymella rabiei). A combination of TAIL and inverse PCR extended the MAT1-2 sequence in both directions, then primers designed to MAT1-2 flanking DNA were used to amplify the entire MAT1-1 idiomorph. MAT1-1 and MAT1-2 idiomorphs were 2294 and 2693 bp in length, respectively, and each contained a single putative open reading frame (ORF) and intron similar to MAT loci of other loculoascomycete fungi. MAT genes were expressed at high levels in rich medium. MAT-specific PCR primers were designed for use in a multiplex PCR assay and MAT-specific PCR amplicons correlated perfectly to mating phenotype of 35 ascospore progeny from a cross of MAT1-1 by MAT1-2 isolates and to the mating phenotype of field-collected isolates from diverse geographic locations. MAT-specific PCR was used to rapidly determine the mating type of isolates of A. rabiei sampled from chickpea fields in the US Pacific Northwest. Mating type ratios were not significantly different from 1:1 among isolates sampled from two commercial chickpea fields consistent with the hypothesis that these A. rabiei populations were randomly mating. The mating type ratio among isolates sampled from an experimental chickpea field where asexual reproduction was enforced differed significantly from 1:1. A phylogeny estimated among legume-associated Ascochyta spp. and related loculoascocmycete fungi using sequence data from the nuclear ribosomal internal transcribed spacer (ITS) demonstrated the monophyly of Ascochyta/Didymella spp. associated with legumes but was insufficiently variable to differentiate isolates associated with different legume hosts. In contrast, sequences of the HMG region of MAT1-2 were substantially more variable, revealing seven well-supported clades that correlated to host of isolation. A. rabiei on chickpea is phylogenetically distant from other legume-associated Ascochyta spp. and the specific status of A. rabiei, A. lentis, A. pisi, and A. fabae was confirmed by the HMG phylogeny
The historical and contemporary population genetic structure of the chickpea Ascochyta blight pathogen, Ascochyta rabiei (teleomorph: Didymella rabiei), was determined in the US Pacific Northwest (PNW) using 17 putative AFLP loci, four genetically characterized, sequence-tagged microsatellite loci (STMS) and the mating type locus (MAT). A single multilocus genotype of A. rabiei (MAT1-1) was detected in 1983, which represented the first recorded appearance of Ascochyta blight of chickpea in the PNW. During the following year many additional alleles, including the other mating type allele (MAT1-2), were detected. By 1987, all alleles currently found in the PNW had been introduced. Highly significant genetic differentiation was detected among contemporary subpopulations from different hosts and geographical locations indicating restricted gene flow and/or genetic drift occurring within and among subpopulations and possible selection by host cultivar. Two distinct populations were inferred with high posterior probability which correlated to host of origin and date of sample using Bayesian model-based population structure analyses of multilocus genotypes. Allele frequencies, genotype distributions and population assignment probabilities were significantly different between the historical and contemporary samples of isolates and between isolates sampled from a resistance screening nursery and those sampled from commercial chickpea fields. A random mating model could not be rejected in any subpopulation, indicating the importance of the sexual stage of the fungus both as a source of primary inoculum for Ascochyta blight epidemics and potentially adaptive genotypic diversity.
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