Dissertations / Theses on the topic 'Ascochyta blight'

Bibliography: leaves 111-120. This study investigated various aspects of genetic resistance in fava beans to Ascochta blight (A. fabae) with the objective to facilitate an efficient breeding strategy for long-term control. Pathogenic variability of A. fabae was found to be high, as was genetic variation between resistant fava bean accessions. A number of alternative resistance genes to that of Ascot cultivar were identified.

Bibliography: leaves 182-217. This study was conducted to determine the etiology of a blight disease of chickpea in south-eastern Australia and the factors affecting disease development. The disease had previously been identified as phoma blight. Pathogenicity testing revealed two isolates subsequently identified as Asochyta rabiei, the first conclusive identification in the southern hemisphere. Greenhouse screening of chickpea varieties identified types resistant to ascochyta blight. The effects of plant age and environmental conditions on disease development were investigated under controlled conditions in growth rooms. Seedlings were more susceptible than older plants. The optimum conditions for ascochyta blight were 20° C and a 48-96 h period of leaf wetness. Through field trials it was found that disease intensity increased over time, especially in cv. Desavic. The means of penetration of the chickpea host was established in histological studies. This study provided advance warning of this disease for the expanding chickpea industry, and has allowed the implementation of appropriate disease management strategies. It is recommended that cv. Desavic should not be grown where ascochyta blight is likely to be a problem.

Ascochyta blight, caused by Ascochyta rabiei (Pass.) Labrousse, is one of the most destructive diseases of chickpea (Cicer arietinum L.) worldwide. Despite the existence of highly resistant uncultivated genotypes, attempts to develop cultivars with a high level of durable resistance have been unsuccessful. This study investigated the chickpea defence response to A. rabiei using a functional genomics approach, which has the capacity to improve the overall understanding of the coordinated defence response at a molecular level. An existing cDNA library was used to generate a resource of Expressed Sequence Tags (ESTs) that, after clustering, comprised 516 unigenes. The unigenes were functionally annotated resulting in the identification of 20 specific defence-related unigenes, as well as numerous transcripts with possible involvement in the coordination of defence responses. To explore the expression patterns of the defence-related unigenes in an A. rabiei resistant and susceptible genotype, the unigenes were employed as probes in microarrays. Resulting expression data was analysed to identify differentially expressed unigenes over a time-course after infection. Comparison of the expression profiles from the resistant and susceptible genotype identified three putative genes that were exclusively up-regulated in the resistant genotype, thus may be involved in an effective defence response. Considering that a defence response can involve hundreds of genes, the entire set of chickpea unigenes were used to construct large-scale microarrays. To supplement the chickpea probes, 156 putative defence-related grasspea (Lathyrus sativus L.) ESTs and 41 lentil (Lens culinaris Med.) Resistance Gene Analogs (RGAs) were also included. Expression profiles for three chickpeas and one wild relative were generated over a time course. 97 differentially expressed ESTs were identified using a robust experimental system that included confirmation by quantitative RT-PCR. The results indicated that genes involved in the active defence response were similar to those governed by R-gene mediated resistance, including the production of reactive oxygen species and the hypersensitive response, down-regulation of 'housekeeping' gene expression, and expression of pathogenesis-related proteins. The comparison between resistant and susceptible genotypes identified certain gene expression 'signatures' that may be predictiv e of resistance. To further characterise the regulation of potential defence-related genes, the microarray was used to study expression profiles of the three chickpea genotypes (excluding the wild relative) after treatment with the defence signalling compounds, ethylene (E), salicylic acid (SA), and jasmonate (JA). 425 ESTs were differentially expressed, and comparison between genotypes revealed the presence of a wider range of inducible defence responses in resistant genotypes. Linking the results with the previous microarray results indicated the presence of other pathogen-specific signalling mechanisms in addition to E, SA and JA. The lower arsenal of defence-related gene expression observed in the susceptible genotype may be a result of 'breaks' in the pathways of defence-related gene activation. To draw together the findings of all experiments, a model was constructed for a hypothetical mechanism of chickpea resistance to A. rabiei. The model was synthesised based on the evidence gathered in this study and previously documented defence mechanisms in chickpea, and identified signal transduction as a key to resistance.

Ascochyta blight is the most common disease of economic importance in peas (Pisum sativum L.) in North Dakota. Selection based on molecular markers would greatly facilitate identification of resistant varieties. A mapping population comprised of 394 F7-derived recombinant inbred line (RILs) and derived from the cross `Lifter'/'Radley' was developed to study resistance to Ascochyta blight. A genetic map was developed based on 179 loci including SSR, RAPD, and CAPS markers, distributed on seven linkage groups. Phenotyping for reaction to Ascochyta blight was carried out under greenhouse and field conditions. Five replicate plants were scored using a 0 to 5 scale, where 0 = no disease and 5 = plant death. Forty-three lines showed a high level of resistance and QTL analysis identified ten DNA markers associated with Ascochyta blight resistance genes. This genetic map will provide additional insight to localize disease resistance genes/QTLs and aid development of resistant varieties.

Ascochyta rabiei is the causal agent of blight of chickpea, an important food legume crop for human populations in Developing Countries. All reliably identified isolates of the fungus produce toxins in culture, known as the solanapyrones, of which solanapyrone A is the most frequently found and also the most toxic. The principal aim of the project was to determine the role of this toxin in the disease syndrome by producing toxin-minus mutants and testing them for virulence. Four transformation techniques were attempted: Restriction Enzyme Mediated Integration (REMI), electroporation, particle bombardment and Agrobacterium tumefaciens-mediated transformation. With the last, employing a T-DNA containing a hygromycin resistance gene, 908 transformants were obtained from germinated pycnidiospores on a selective medium containing hygromycin. Genuine transformants were tested for the production of solanapyrone A using an assay in microtitre plates. Loss of toxin production by transformants was confirmed by reversed phase High Performance Liquid Chromatography. Sixteen transformants produced significantly less solanapyrone A than the wild-type strain. Transformants were also screened for integration events by PCR, using primers specific to the hygromycin resistance gene and homologous hybridisation to a probe consisting of this gene. Among the four transformants tested, three have integrated two copies of T-DNA and one had a single insertion. In order to optimise the production of solanapyrone A so as to provide a source of the compound for screening chickpea genotypes, three types of cultures of A. rabiei were tested: still culture, shake culture and fermenter culture. The toxin was purified from culture filtrates by solvent partitioning followed by flash chromatography. The effect of two safeners on the sensitivity of chickpea shoots to solanapyrone A was tested using bioassays. Dichlormid (300 or 800 g per shoot) and fenclorim (18 g per shoot) decreased the sensitivity of chickpea shoots to solanapyrone A 1.6 and 2.5-fold, respectively.

[Truncated abstract] The genetics of ascochyta blight resistance was studied in five 5 x 5 half-diallel cross sets involving seven genotypes of chickpea (ICC 3996, Almaz, Lasseter, Kaniva, 24B-Isoline, IG 9337 and Kimberley Large), three accessions of Cicer reticulatum (ILWC 118, ILWC 139 and ILWC 184) and one accession of C. echinospermum (ILWC 181) under field conditions. Both F1 and F2 generations were used in the diallel analysis. Almaz, ICC 3996 and ILWC 118 were the most resistant genotypes. Estimates of genetic parameters, following Hayman's method, showed significant additive and dominant gene actions. The analysis also revealed the involvement of both major and minor genes. Susceptibility was dominant over resistance to ascochyta blight. The recessive alleles were concentrated in the two resistant chickpea parents ICC 3996 and Almaz, and one C. reticulatum genotype ILWC 118. High narrow-sense heritability (ranging from 82 to 86% for F1 generations, and 43 to 63% for F2 generations) indicates that additive gene effects were more important than non-additive gene effects in the inheritance of the trait and greater genetic gain by breeding resistant chickpea cultivars using carefully selected parental genotypes. Current simple leaf varieties are often susceptible to ascochyta blight disease whereas varieties of other leaf types range from resistant to susceptible. The inheritance of ascochyta blight resistance and different leaf types and their correlation were investigated in intraspecific progeny derived from crosses among two resistant genotypes with normal leaf type (ICC 3996 and Almaz), one susceptible simple leaf type (Kimberley Large) and one susceptible multipinnate leaf type (24 B-Isoline). ... An interspecific F2 mapping population derived from a cross between chickpea accession ICC 3996 (resistant to ascochyta blight, early flowering, and semi-erect plant growth habit) and C. reticulatum accession ILWC 184 (susceptible to ascochyta blight, ii late flowering, and prostrate plant growth habit) was used for constructing a genetic linkage map. F2 plants were cloned through stem cuttings taken at pre-flowering stage, treated with plant growth regulator powder (0.5 mg/g indole butyric acid (IBA) and 0.5 mg/g naphthalene acetic acid (NAA)) and grown in a sand + potting mix substrate. Clones were screened for ascochyta blight resistance in controlled environment conditions using a 19 scale. Three quantitative trait loci (QTLs) were found for ascochyta blight resistance in this population. Two linked QTLs, located on linkage group (LG) 4, explained 21.1% and 4.9% of the phenotypic variation. The other QTL, located on LG3, explained 22.7% of the phenotypic variation for ascochyta blight resistance. These QTLs explained almost 49% of the variation for ascochyta blight resistance. LG3 had two major QTLs for days to flowering (explaining 90.2% of phenotypic variation) and a major single QTL for plant growth habit (explaining 95.2% of phenotypic variation). There was a negative correlation between ascochyta blight resistance and days to flowering, and a positive correlation between days to flowering and plant growth habit. The flanking markers for ascochyta blight resistance or other morphological characters can be used in marker-assisted selections to facilitate breeding programs.

Chickpea is one of the most important leguminous crops grown in regions of southern Europe, Asia, the Middle East, and the United States. Ascochyta blight, caused by Ascochyta rabiei, is the most important foliar disease of chickpea. In favorable conditions, this disease can destroy the entire chickpea field within a few days. In this project the secreted proteins of Ascochyta rabiei have been characterized through one and two-dimensional polyacrylamide gel electrophoresis. This is the first proteomic study of the A. rabiei secretome, and a standardized technique to study the secreted proteome has been developed. A common set of proteins secreted by this pathogen and two isolates that exhibit the maximum and minimum number of secreted proteins when grown in modified Fries and Czapek Dox media have been identified. Population genetic studies of Ascochyta rabiei populations in North Dakota have been conducted using microsatellites and AFLP markers. Population genetic studies have shown that the ascochyta population in North Dakota has not changed genetically in the years 2005, 2006 and 2007, but the North Dakota population is different from the baseline population from the Pacific Northwest. The ascochyta population in North Dakota is a randomly mating population, as shown by the mating type ratio.

Research objective and experimental tasks. The study was designed to explore the incidence and severity of root and foot rots and ascochyta blight in field pea crops and to identify the measures and practices for the prevention and control of the diseases caused by the pathogens of Ascochyta complex. Experimental tasks: - To identify the susceptibility of various field pea varieties to root and foot rots and ascochyta blight under different agro-ecological conditions. - To establish the effect of meteorological factors on the severity of root and foot rots and ascochyta blight in field pea crops. - To determine the frequency of detection of pathogens of Ascochyta complex on various pea varieties. - To estimate the feasibility of control of the diseases caused by the pathogens of Ascochyta complex using seed treatment and fungicide application. - To assess the impact of seed treatment and fungicide application on field pea productivity and yield components. - To study the possible side-effect of the chemical seed treatment on the microflora of pea rhizosphere and soil.
Tyrimų tikslas ir uždaviniai. Tyrimais siekta ištirti šaknų, pašaknio puvinių ir askochitozės išplitimą bei žalingumą sėjamojo žirnio pasėliuose, nustatyti Ascochyta komplekso patogenų sukeliamų ligų prevencijos ir kontrolės priemones. Tyrimų uždaviniai: - Nustatyti įvairių sėjamojo žirnio veislių jautrumą šaknų, pašaknio puviniams ir askochitozei skirtingomis agroekologinėmis sąlygomis. - Nustatyti meteorologinių faktorių įtaką šaknų, pašaknio puvinių ir askochitozės intensyvumui žirniuose. - Nustatyti Ascochyta komplekso patogenų aptikimo dažnį ant įvairių veislių žirnių. - Įvertinti Ascochyta komplekso patogenų sukeliamų ligų kontrolės galimybę naudojant beicus ir fungicidus. - Įvertinti beicų ir fungicidų įtaką žirnių derlingumui ir derliaus komponentams. - Ištirti galimą cheminių beicų šalutinį poveikį žirnių rizosferos bei dirvožemio mikroflorai.

The inheritance of resistance to ascochyta blight in lentil (Lens culinaris Medik.) caused by Ascochyta fabae Speg. f. sp. lentis Gossen et al (Syn. A. lentis Vassil.) was studied using as parents the Canadian cultivars Eston (susceptible) and Laird (moderately resistant) and two resistant lines from ICARDA, ILL-5588 and ILL-5684. The F2, F2-derived Fa families and F2-derived F4 families of each cross were evaluated for ascochyta resistance under field conditions in an ascochyta nursery during 1987, 1988 and 1989, respectively. The parents and segregating populations were rated for ascochyta reaction on the basis of foliage symptoms, using a 1 to 9 disease rating scale, with plants rated 1 to 5 considered resistant and plants rated 7 to 9 considered susceptible. In addition percent seed-borne ascochyta infection was evaluated, using the seed plating technique. The cuItivar Eston was susceptible. Laird lentil was resistant to foliar infection by ascochyta, but its resistance breaks down in the late podding stage and under the wet conditions of the ascochyta nursery percent seed-borne ascochyta infection was even higher than in the susceptible cultivar Eston. The lines ILL-5588 and ILL-5684 were highly resistant with resistance persisting after maturity and the seed coats do not become infected and discolor materially even with prolonged exposure to wet weather at harvest. A chi-square test for goodness-of-fit of the F2 and F2- derived F3 families indicated that resistance to foliar infection by ascochyta in Laird lentil was conditioned by a single recessive gene, ral1• Results also indicated that the resistance to foliage and seed infection by ascochyta of ILL- 5588 and ILL-5684 was due to two - dominant genes,' Ral2 and Ral3. ILL-5588, but not ILL-5684, also carried the ral1 gene for resistance to foliar infection by ascochyta and is the better source of resistance to ascochyta. The high correlation between percent seed-borne ascochyta infection in Fz-derived F3 families and in F2-derived F4 families plus the medium to high heritability estimates (0.52 to 0.8l) indicate that it will be easy to select for ascochyta resistance in these crosses. An effective method of selecting for ascochyta resistance in lentil was developed. An ascochyta nursery is developed by spreading infected lentil straw between the lentil rows prior to flowering. This nursery is then sprinkled intermittently once or twice each day until about two weeks after maturity. The crop is permitted to dry naturally and selections made for ascochyta resistant F2 plants or replicated progeny rows in later generations. Ascochyta resistance is based on a low level of discolored seed (0 to 5%), reconfirmed by plating the seed to determine percent seed-borne ascochyta infection in replicated progeny rows. Only a few selections have a high level of clean bright seed and require seed planting. This technique is quick, easy, effective and efficient. Resulting selections are resistant to both foliar infection and seed infection by ascochyta.

Lentil (Lens culinaris) is a major grain legume (pulse) crop in Canada. Ascochyta blight, caused by Ascochyta lentis Kaiser et aI. (1997) (syn. Ascochyta fabae Speg. f sp. lentis Gossen et aI., 1986) is an important disease of lentil in Canada and worldwide. This disease can be serious, especially in wet growing seasons, and losses can be as high as 70% due to reduction in yield and quality. The main objective of this study was to determine the mode of inheritance of resistance to seedborne ascochyta blight in lentil. Seven lentil cultivars/lines, four resistant (ILL 5588, Indianhead, PI 339283 and PI 374118 (tentative)) and three susceptible (Eston, Laird and ZT4), were crossed in all possible combinations, excluding reciprocals. Fl plants were grown in the greenhouse and spaced F2 plants were grown in an irrigated ascochyta nursery. F2 plants were harvested individually and seeds were plated on agar media to determine percentage seedborne ascochyta infection. F2 plants with [greater than or equal too] 12% seedborne ascochyta infection were considered resistant and those with > 12% seedborne ascochyta infection were considered susceptible. F3 rows were grown in an irrigated ascochyta nursery in the field and harvested in bulk. One hundred seeds from each of the F3 rows were plated on agar media and percentage seedborne ascochyta infection was determined. F3 families with [greater than or equal to] 12% seedborne ascochyta infection were considered resistant and those with > 12% seedborne ascochyta infection were considered susceptible. Chi-squared test of goodness-of-fit to various one and two gene ratios showed that the resistance in Indianhead lentil was governed by a single recessive gene. Resistance in ILL 5588 lentil was governed by a single dominant gene. The resistance in PI 339283 was governed by at least one dominant gene. Lentil line PI 374118 showed a high level of seedborne ascochyta infection and was regarded as susceptible. The recessive gene governing resistance in Indianhead lentil was epistatic to the dominant genes for resistance in ILL 5588 and PI 339283 lentil. Indianhead lentil showed high foliage infection by ascochyta, suggesting that resistance to seedborne ascochyta infection and resistance to foliage infection are controlled by two different genetic systems.

The aim of this study was to gain insight into the nature of resistance genes and mechanisms of resistance present in different ascochyta blight (AB) resistant genotypes of lentil to efficiently select non-allelic AB resistance genes mediating different mechanisms of resistance for gene pyramiding. Recombinant inbred lines (RILs) from all possible crosses among AB resistant Lens culinaris genotypes CDC Robin, 964a-46, ILL 7537 and ILL 1704 were subjected to allelism tests. Efforts were also made to understand the genetics of resistance in the L. ervoides accession L-01-827A. LR-18, a RIL population from the cross CDC Robin × 964a-46 was subjected to quantitative trait loci (QTL) mapping using a comprehensive genetic linkage map previously developed from polymorphic SNPs, SSRs and phenotypic markers. Results of allelism tests suggested that genes conditioning resistance to ascochyta blight in all lentil genotypes were non-allelic. Two complementary recessive resistance genes in L-01-827A were detected. QTL analysis indicated that CDC Robin and 964a-46 were different at two AB resistance QTLs. Histological tests suggested that cell death inhibition in CDC Robin, and reduced colonization of epidermal cells in 964a-46 might be the mechanisms of resistance in these genotypes. Comparing the expression of key genes in the salicylic acid (SA) and jasmonic acid (JA) signaling pathways of CDC Robin and 964a-46 suggested that the SA pathway was strongly triggered in 964a-46. However, the JA pathway was triggered in both, but at a lower expression level in 964a-46 than in CDC Robin. RNA-seq analysis revealed a number of candidate defense genes differentially expressed among genotypes with hypothetical actions in different layers of the plant defense machinery. The expression levels of the six candidate defense genes measured by quantitative real-time PCR analysis was correlated with those of RNA-seq. In conclusion, 964a-46 and CDC Robin mediated resistance to ascochyta blight through different resistant mechanisms, making them ideal candidates for resistance gene pyramiding. Gene pyramiding can be accelerated using closely linked markers to CDC Robin and 964a-46 resistance genes identified through QTL analysis.

Field pea is an important annual crop due to its contribution to soil fertility and other rotational benefits. However, weeds and ascochyta blight limit pea yield, particularly in organic systems. Leafed and semi-leafless pea types differ in lodging resistance, and may affect weeds and disease through differences in canopy light penetration and air flow. Mixtures of the two leaf types may improve weed and disease suppression and yield compared with monocultures of the same cultivars. To test this hypothesis, replicated field experiments were conducted under organic and conventional management in Saskatoon and Vonda, SK, in 2011 and 2012. Mixtures of a leafed and semi-leafless cultivar, CDC Sonata and CDC Dakota, were sown in ratios of 0:100, 25:75, 50:50, 75:25, and 100:0 leafed to semi-leafless pea, at target seeding rates of 88 and 132 plants m-2. Conventionally managed plots were inoculated with ascochyta blight-infested pea straw and received overhead irrigation to encourage disease. Mixtures of 50% or more semi-leafless pea adopted the greater lodging resistance and weed suppression of the semi-leafless cultivar. Mixtures comprised of 25% leafed and 75% semi-leafless pea increased both seed and biomass yield compared with either cultivar grown alone. Yield enhancement was attributed to the leafed cultivar, whose seed yield was 76% higher in mixture than expected based on monoculture yield. Ascochyta blight epidemics were of moderate severity, and leafed and semi-leafless monocultures reached 36 and 43% necrosis in 2011, and 33 and 38% necrosis in 2012, respectively. The disease reaction of mixtures fell between the two component cultivars. At disease onset in 2012, lower light interception and shorter moisture durations coincided with the lower ascochyta blight severity of leafed monocultures. In 2011 and the later phase of the 2012 epidemic, disease severity was negatively associated with vine length, and positively associated with number of nodes and tissue senescence. Despite the advantages of leafed and semi-leafless pea mixtures, the limited selection of leafed cultivars impedes adoption of this technique by growers. For pea breeders, developing mixtures of pea lines isogenic for leaf type may increase yield compared with single cultivars.

Chickpea (Cicer arietinum L.) was recently introduced to the Canadian prairies, a region which has a short growing season in which crop maturation often occurs under cool and wet conditions. To improve the yield of chickpea, crop duration must closely match the available growing season. The objectives of this study were to: i) examine the days to flowering of diverse chickpea accessions grown in either long or short-days; ii) examine the days to flowering of selected chickpea accessions grown in a range of thermal regimes combined with either long or short days and to examine the interaction between photoperiod and day and night temperatures on crop duration; iii) determine the timing and duration of the photoperiod-sensitive phase in selected chickpea accessions, and vi) determine the genetic basis of the association between flowering time and reaction to ascochyta blight in chickpea. A wide variation was observed in chickpea accessions for their response to flowering under long (16/8 hours day /night) and short days (10/14 hours day/night). Earlier flowering was observed under long photoperiod regimes compared with the short photoperiod regimes. Variability was detected among chickpea accessions for their flowering responses when different temperatures were combined with different photoperiods. Earlier flowering was observed under long days (16/8 hours day/night) coupled with high to moderate temperature regimes (24/16 ºC and 20/12 ºC, day and night respectively) compared to short-days (10/14 hours day and night) and moderate to low temperature regimes (20/12 ºC and 16/8 ºC day and night, respectively). Those chickpea accessions such as ICC 6821 and ICCV 96029 which originated from the lower latitudes of Ethiopia and India, respectively, flowered earlier compared to accessions such as CDC Corinne and CDC Frontier which originated from the higher latitudes and cooler temperate environments of western Canada. Photoperiod sensitivity phases were detected in chickpea accessions adapted to the cold environments of western Canada, whereas no photoperiod sensitivity phase was identified in the extra-early flowering cultivar ICCV 96029. The duration of the photoperiod sensitive phase in the chickpea accessions was longer under short days compared to long days. Field and growth chamber evaluation of a chickpea RIL population (CP-RIL-1) revealed the presence of variability among the lines and the two parents for their days to flowering and level of resistance to ascochyta blight. Broad sense heritability across different site-years for days to flower 0.45 to 0.78, plant height 0.48 to 0.78, ascochyta blight resistance 0.14 to 0.68, days to maturity 0.26, photoperiod sensitivity 0.83 and nodes number of first flowering 0.37 to 0.75 were estimated. Days to flower and photoperiod sensitivity were significantly r = -0.21 to -0.58 (P ≤ 0.05 to 0.001) and -0.28 to -0.41 (P ≤ 0.01 to 0.001), respectively and negatively correlated with ascochyta blight resistance in the CP-RIL-1 population. A genetic linkage map consisting of eight linkage groups was developed using 349 SNP markers. Seven QTLs were identified for days to flowering under growth chamber and field conditions on chromosomes 3, 5, 6 and 8 each and 3 QTLs on chromosome 4. The total phenotypic variation explained by QTLs for days to flowering ranged from 7 to 44%. Two QTLs for days to maturity were identified on chromosomes 3 and 8. Three QTLs, one each on chromosomes 3, 4 and 5 were identified for photoperiod sensitivity. The total phenotypic variation explained by each QTL for photoperiod sensitivity ranged from 7 to 41%. A total of three QTL for node of first flowering, one on chromosomes 3 and 8 each, and two on chromosome 4 were identified. The two QTL on chromosome 4 explained total phenotypic variations of 11 and 32%, respectively. Ten QTLs distributed across all chromosomes, except chromosomes 2 and 5, were identified for ascochyta blight resistance. The phenotypic variability explained by each QTL for ascochyta blight resistance ranged from 7 to 17%. The molecular markers associated with these QTLs have potential for use in chickpea breeding.