新疆鹰嘴豆壳二孢疫病病菌Ascochyta rabiei交配型、致病力及其对3种杀菌剂的敏感性测定

新疆是我国鹰嘴豆主要生产地,然而随着鹰嘴豆种植面积的扩大,集约化种植模式的发展以及广泛从国内外引种,鹰嘴豆壳二孢疫病(Ascochyta blight)开始发生。由于该病害在新疆发生历史较短,相关的研究还甚少。本研究对新疆鹰嘴豆壳二孢疫病病菌Ascochyta rabiei的交配型、致病力及对3种杀菌剂敏感性进行测定,结果表明,A.rabiei的交配型MAT1-1和MAT1-2在新疆木垒地区的分离频率明显偏离1∶1,以MAT1-2为优势种群,但其致病力与MAT1-1无显著差异,而MAT1-1对30%醚菌酯EC的敏感性显著低于MAT1-2。     

Characterization of chickpea differentials for pathogenicity assay of ascochyta blight and identification of chickpea accessions resistant to Didymella rabiei

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.     

Development of the teleomorph of Ascochyta rabiei on culture media

Ascochyta blight caused by Didymella rabiei (anamorph: Ascochyta rabiei) is an important foliar disease of chickpea in many countries. The fungus is heterothallic and requires the pairing of two compatible mating types for the teleomorph to develop. In nature, the teleomorph only develops on chickpea debris that overwinters on the soil surface in the presence of both mating types. When natural and synthetic agar media were seeded with conidial suspensions of compatible isolates of D. rabiei from Spain and the United States and incubated under favourable conditions for teleomorph development, the teleomorph only developed on 2?% water agar amended with powdered chickpea stems or hot water extracts of chickpea stems, but not on 14 other natural or synthetic media. Ascospore isolates of D. rabiei from pseudothecia that developed on agar media were indistinguishable in cultural and morphological characteristics from isolates of the fungus from chickpea. Production of pseudothecia and ascospores on the best culture medium was always lower than on stem pieces of chickpea straw used as a control treatment. Ascospores discharged from pseudothecia that developed on powdered chickpea stem media onto chickpea seedlings were pathogenic, inducing symptoms identical to those caused by ascospores from chickpea stem pieces or conidia from a chickpea isolate of the fungus. This is the first report of the teleomorph of D. rabiei developing on culture media.     

Mating type, pathotype and RAPDs analysis inDidymella rabiei, the agent of ascochyta blight of chickpea

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.     

Different ecological affinities and aggressiveness patterns among Didymella rabiei isolates from sympatric domesticated chickpea and wild Cicer judaicum

Domesticated chickpea (Cicer arietinum) and its wild relative C. judaicum grow in sympatric distribution in Israel and both are susceptible to Ascochyta blight caused by Didymella rabiei. C. arietinum was grown for millennia in drier and hotter Levantine spring conditions while C. judaicum grows in the wetter and milder winters. Accordingly, it is possible that D. rabiei isolates originated from C. arietinum are adjusted to the less favorable spring conditions. Here, 60 isolates from both origins were tested in vitro for their hyphal growth at 15 and 25 degrees C. Isolates from C. arietinum had a significantly larger colony area at 25 degrees C than at 15 degrees C (P < 0.001) while no such differences were detected between isolates from C. judaicum. D. rabiei isolates from wild and domesticated origins were used to inoculate nine C. judaicum accessions and two domesticated chickpea cultivars and their aggressiveness patterns were determined using five measures. On domesticated chickpea, isolates from domesticated origin were significantly more aggressive in four out of the five aggressiveness measures than isolates from wild origin. On C. judaicum, isolates from wild origin were generally more aggressive than isolates from domesticated origin. The results suggest that the habitat segregation between wild and domesticated Cicer influences the pathogens ecological affinities and their aggressiveness patterns.     

Adaptation to host (chickpea) genotype by isolates of Didymella rabiei following repeated cycles of infection

Journal of Plant Diseases and Protection - Ascochyta blight of chickpea (Cicer arietinum), caused by Didymella rabiei, is an important disease of chickpea world- wide. Under favourable conditions,...     

Baseline sensitivity and the population shifts of Didymella rabiei in chickpea to the QoI fungicide pyraclostrobin in Alberta,Canada

Journal of Plant Diseases and Protection - Ascochyta blight, caused by Didymella rabiei, is one of the most important factors limiting chickpea production worldwide. In western Canada repeated...     

Population structure and mating system of Ascochyta rabiei in Tunisia: evidence for the recent introduction of mating type 2

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, G _ST = 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 ( H _T = 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.     

Epiphytotics of chickpea Ascochyta blight in Turkey as influenced by climatic factors

Journal of Plant Diseases and Protection - Chickpea Ascochyta blight caused by Didymella rabiei is one of the most important fungal diseases affecting yield and seed quality negatively in Turkey....     

Structure and pathogenic variability in Ascochyta rabiei populations on chickpea in the Canadian prairies

A population study of Ascochyta rabiei from the Canadian prairies was conducted to assess pathogenicity among isolates with the objectives to investigate the existence of a race or pathotype structure and to evaluate whether there had been a shift to higher aggressiveness between 1998 and 2002. Ninety-nine isolates collected in 1998, 2001 and 2002 were inoculated onto seven differential chickpea genotypes. Significant isolate × differential interactions occurred, but accounted for a small proportion of the total variability. It was found that very few interaction effects between all combinations of differentials and isolates were significant and frequency distributions of disease severity of isolates tested on the differentials revealed continuous distributions. These results suggest that no genotype-specific relationship existed between A. rabiei and its host and that Canadian populations of the pathogen cannot be objectively classified into races or pathotypes. Isolates from 2001 and 2002 caused significantly more disease than isolates from 1998, suggesting that disease epidemics encountered since 1999 were in part caused by a shift in the population to higher aggressiveness.     

Alternative hosts and plant tissues for the survival,sporulation and spread of the Ascochyta blight pathogen of chickpea

Various crop and weed species were infected naturally by Didymella rabiei (anamorph: Ascochyta rabiei) in blight-affected chickpea fields in the Palouse region of eastern Washington and northern Idaho, USA. The fungus was isolated from asymptomatic plants of 16 species commonly found in commercial crops in this region. Isolates of the pathogen from crop and weed species were pathogenic to chickpea and indistinguishable in cultural and morphological characteristics from isolates of D. rabiei from chickpea. Both mating types of D. rabiei were isolated from eight naturally infected plant species. Chickpeas were infected by D. rabiei when plants emerged through infested debris of seven crop and weed species. The teleomorph developed on overwintered tissues of seven plant species infected naturally by D. rabiei in a blight screening nursery and on debris of wheat, white sweet clover and pea inoculated with ascospores of D. rabiei or conidia of two compatible isolates of the pathogen. Didymella rabiei naturally infected 31 accessions of 12 Cicer spp. and the teleomorph developed on the overwintered debris of all accessions, including those of three highly resistant perennial species. The fungus developed on the stem and leaf pieces of ten plant species common to southern Spain inoculated with conidia of two compatible isolates of D. rabiei, and formed pseudothecia with asci and viable ascospores on six of ten species and pycnidia with conidia on all plant species.     

Synthesis of the solanapyrone phytotoxins by Ascochyta rabiei in response to metal cations and development of a defined medium for toxin production

The phytotoxic solanapyrones A, B and C, were produced by Ascochyta rabiei when grown on Czapek Dox nutrients supplemented with an aqueous extract of chickpea seed but not when grown on Czapek Dox nutrients alone. Addition of amino acids, vitamins and inorganic ions to Czapek Dox nutrients allowed the production of the solanapyrones in good yields. By systematic elimination of components of this medium, the constituents essential for toxin production were identified as the divalent metal cations Zn²⁺, Ca²⁺, Mn²⁺ and Cu²⁺. When these ions were added to Czapek Dox nutrients in the same concentrations as those found in chickpea extract, concentrations of the phytotoxins similar to those found in Czapek Dox nutrients supplemented with chickpea extract were detected. Removal of cations from the chickpea supplement by a cation exchange resin did not affect the growth of the fungus compared with growth on the medium containing the complete supplement, but no toxin was produced. A defined medium and cultural conditions suitable for solanapyrone production by A. rabiei are described.     

Biometric Analyses of the Inheritance of Resistance to Didymella rabiei in Chickpea

ABSTRACT Historically, the response of chickpea (Cicer arietinum L.) to Didymella rabiei (causal agent of Ascochyta blight) has been mainly related to as complete resistance and it was commonly assayed with qualitative (nonparametric) scales. Two reciprocal populations, derived from intra-specific crosses between a moderately resistant late flowering Israeli cultivar and a highly susceptible early flowering Indian accession, were tested at F(3) and F(4) generations in 1998 and 1999, respectively. A quantitative (parametric) assessment (percent disease severity) was used to evaluate the chickpea field response to Ascochyta blight. The transformed relative area under the disease progress curve (tRAUDPC) was calculated for each experimental unit for further analyses. Heritability estimates of the tRAUDPC were relatively high (0.67 to 0.85) in both generations for both reciprocal populations. The frequency distributions of tRAUDPC of the populations were continuous and significantly departed from normality (Shapiro-Wilk W test; P of W < 0.0001), being all platykurtic and skewed toward either the resistant or the susceptible parental lines. The presence of major genes was examined by testing the relationship between the F(3) and F(4) family means and the within-family variances (Fain's test). Analyses of these relationships suggested that segregation of a single (or few) quantitative trait locus with major effect and possibly other minor loci was the predominant mode of inheritance. The correlation estimates between the resistance and days to flower (r = -0.19 to -0.44) were negative and significantly (P = 0.054 to 0.001) different from zero, which represents a breeding constraint in the development of early flowering cultivars with Ascochyta blight resistance.     

Sympatric ascochyta complex of wild Cicer judaicum and domesticated chickpea

The aim of this study was to isolate, identify and characterize ascochyta blight pathogens from Cicer judaicum , a wild annual Cicer species which grows in Israel and other Mediterranean countries in sympatric distribution with legume crops, and determine their virulence and aggressiveness to other wild and domesticated legumes. Native C. judaicum plants exhibited symptoms resembling ascochyta diseases of grain legume crops. Two distinct pathogens were isolated and identified as Phoma pinodella and Didymella rabiei using morphological and molecular tools; their infectivity was verified using Koch's postulates. The virulence of these pathogens was examined on 13 legume species, of which P. pinodella was virulent to Pisum sativum , P. fulvum , C. judaicum , C. arietinum , C. reticulatum , C. pinnatifidum and C. bijugum . Didymella rabiei infected all these Cicer species, but not the other legume species tested. Aggressiveness of the pathogens was tested on wild and domesticated chickpea and pea. Didymella rabiei isolated from C. judaicum had significantly higher ( P  < 0·001) aggressiveness than P. pinodella from C. judaicum on both wild and domesticated chickpea. Disease severity on the former species ranged from 62·5% to 70% and on the latter from 41% to 56%. Phoma pinodella isolates from C. judaicum were more aggressive on C. arietinum and P. sativum than on C. judaicum and P. fulvum . Results of the current study suggest that C. judaicum may serve as an alternative host to ascochyta pathogens that endanger chickpea and possibly other crops and wild species growing in close proximity.     

Aggressiveness of eight <Emphasis Type="Italic">Didymella rabiei</Emphasis> isolates from domesticated and wild chickpea native to Turkey and Israel,a case study

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 aggressiveness 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 aggressiveness pattern of D. rabiei on different hosts could have been shaped by adaptation to the distinct ecological niches of wild vs. domesticated chickpea.     

Host Specificity of Ascochyta spp. Infecting Legumes of the Viciae and Cicerae Tribes and Pathogenicity of an Interspecific Hybrid

ABSTRACT Ascochyta spp. (teleomorphs: Didymella spp.) infect a number of legumes, including many economically important species, and the diseases they cause represent serious limitations of legume production worldwide. Ascochyta rabiei, A. fabae, A. pisi, A. lentis, and A. viciae-villosae are pathogens of chickpea (Cicer arietinum), faba bean (Vicia faba), pea (Pisum sativum), lentil (Lens culinaris), and hairy vetch (V. villosa), respectively. Inoculations in the greenhouse and in growth chambers demonstrated that A. fabae, A. lentis, A. pisi, A. rabiei, and A. viciae-villosae were host specific. Isolates caused no visible disease symptoms on "nonhost" plants (plants other than the hosts they were originally isolated from) but were recovered consistently from inoculated, surface-disinfested, nonhost tissues. Interspecific crosses of A. pisi x A. fabae and A. viciae-villosae x A. lentis produced pseudothecia with viable ascospores, and the hybrid status of the ascospore progeny was verified by the segregation of mating type and amplified fragment length polymorphism (AFLP) markers. Interspecific progeny were morphologically normal in culture but exhibited more phenotypic variation compared with progeny from intraspecific crosses. Mating type and the majority of AFLP markers segregated in Mendelian 1:1 ratios in both intraspecific and interspecific crosses. A total of 11 and 7% of AFLP markers showed segregation distortion among progeny from interspecific crosses and intraspecific crosses, respectively; however, this difference was not significant (P = 0.90). Only 30 of 114 progeny isolates from the A. fabae x A. pisi cross inoculated in the greenhouse caused lesions on pea and only 4 caused disease on faba bean. In all, 15 of 110 progeny isolates were pathogenic to pea and none were pathogenic to faba bean under growth chamber conditions. Although no obvious postzygotic, intrinsic isolating barriers were identified in any of the interspecific crosses, it appears that host specialization may act as both a prezygotic, ecological isolating barrier and a postzygotic, extrinsic, ecological isolating barrier in these fungi. Host specificity, coupled with low pathogenic fitness of hybrids, may be an important speciation mechanism contributing to the maintenance of hostspecific, phylogenetic lineages of these fungi.     

Phenotypic variation within a clonal lineage of Phytophthora infestans infecting both tomato and potato in Nicaragua

Late blight caused by Phytophthora infestans (Mont.) de Bary is a constraint to both potato and tomato crops in Nicaragua. The hypothesis that the Nicaraguan population of P. infestans is genotypically and phenotypically diverse and potentially subdivided based on host association was tested. A collection of isolates was analyzed using genotypic markers (microsatellites and mitochondrial DNA haplotype) and phenotypic markers (mating type, virulence, and fungicide sensitivity). The genotypic analysis revealed no polymorphism in 121 of 132 isolates of P. infestans tested. Only the Ia haplotype and the A2 mating type were detected. Most of the tested isolates were resistant to metalaxyl. The virulence testing showed variation among isolates of P. infestans. No evidence was found of population differentiation among potato and tomato isolates of P. infestans based on the genotypic and phenotypic analysis. We conclude that the Nicaraguan population of P. infestans consists of a single clonal lineage (NI-1) which belongs to the A2 mating type and the Ia mitochondrial DNA haplotype. Moreover, based on the markers used, this population of P. infestans does not resemble the population in countries from which potato seed is imported to Nicaragua or the population in neighboring countries. The data presented here indicate that the NI-1 clonal lineage is the primary pathogen on both potato and tomato, and its success on both host species is unique in a South American context.     

Seedborne infection ofAscochyta rabiei in chickpea and its transmission to aerial plant parts

Ascochyta blight of chickpea (Cicer arietinum L.), caused byAscochyta rabiei (Pass.) Labrousse, was found to be both externally as well as internally seedborne in nature, with the external infection being predominant. The pathogen was located primarily on or in the seed coat and in very few cases penetrated into the cotyledons and rarely, to the embryo. Seedling infection resulted from both externally as well as internally seedborne inoculum. The mode of fungal transmission from seed to the foliar plant parts was strictly non-systemic in nature.     

Rational Management of Didymella rabiei in Chickpea by Integration of Genotype Resistance and Postinfection Application of Fungicides

ABSTRACT Various aspects of the integration of genotype resistance and chemical control of Ascochyta blight (caused by Didymella rabiei) in chickpea were examined in field experiments from 1993 to 1999 and in greenhouse experiments. Four commercially available chickpea cultivars representing a range of resistance to D. rabiei were used. The efficacy of chemical control in a highly susceptible cultivar was significantly (P < 0.01) related to the conduciveness of the environment to the pathogen. Adequate disease suppression (>80% control) was achieved when weather supported mild epidemics, but insufficient control (<20%) was achieved when weather supported severe epidemics. The contribution of genotype resistance to disease suppression in a moderately susceptible cultivar varied from <10% when weather supported severe epidemics to approximately 60% when weather supported mild epidemics. Spraying a moderately resistant cultivar resulted in 95% control when weather supported mild epidemics, but only 65% control was achieved when weather supported severe epidemics. The existing level of resistance in a moderately resistant cultivar resulted in 70% control when weather supported severe epidemics; fungicides improved control efficacy significantly to >95%. Under mild epidemics, moderate resistance alone provided >95% control. The level of genotype resistance available in a highly resistant cultivar was sufficient to suppress the disease under all weather conditions, even without application of fungicides. The possibility of relying on postinfection rather than prophylactic application of fungicides was tested in the greenhouse and in four field experiments. Activity of the systemic fungicide tebuconazole was detected when the fungicide was applied up to 3 days postinfection, and application of tebuconazole or difenoconazole in the field as a postinfection treatment (i.e., after rain or overhead irrigation) suppressed the disease as effectively as preventive applications and required fewer sprays. In two experiments, the interaction between genotype resistance and chemical control at various amounts of irrigation applied via overhead sprinklers (as a simulation of rain) was tested. The results show that both the level of genotype resistance and the quantity of water should be taken into account in deciding whether to apply a postinfection spray.     

Ultrastructural Studies of conidiogenesis ofAscochyta rabiei, the causal Organism of chickpea blight

Studies employing transmission (TEM) and scanning (SEM) electron microscopy revealed that conidiogenous cells of the chickpea blight fungus,Ascochyta rabiei (Pass.) Labr., resembled phialides in most of their features. The phialides were generally of a simple type, but occasionally they proliferated in a percurrent fashion. There is enough evidence to suggest that the fungus is better placed in genusPhoma. SEM has been employed for the first time to study internal details of fructifications of a closed type in coelomycete fungi.