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.

/pdf/ascochyta-blight-of-chickpea-cicer-arietinum-l-a-review-of-3jxc32gced.pdf

Ascochyta blight of chickpea (Cicer arietinum L.): a review of biology, pathogenicity, and disease management

Chickpea (Cicer arietinum L.) is an important grain legume crop in Asia, Africa and Central and South America. Ascochyta blight caused by Ascochyta rabiei (Pass.) Lab. is one of the most serious diseases of the crop and severe epidemics have been reported. The available literature on Ascochyta blight is reviewed in order to ascertain the present status of knowledge of the disease and to identify the areas of research which need immediate attention. Distribution, yield losses, symptoms, taxonomy, reproduction, epidemiology and control of the disease are discussed. Further information on sexual reproduction, epidemiology and control is needed.

/pdf/a-review-of-ascochyta-blight-of-chickpea-kf21gy4hwe.pdf

A review of Ascochyta blight of chickpea

Coelomycetous fungi are an artificial taxonomic group which produce conidia inside a cavity i.e. conidiomata. Coelomycetes comprise about, 1000 genera and 7000 species, which can be endophytic, pathogenic or saprobic. Traditional classification of coelomycetes was previously based on morphology, such as the shape of conidiomata and mode of conidiogenesis, while it was treated as a distinct group i.e. Deuteromycotina. Sequence based taxonomic studies has been used to accommodate asexual fungi in a natural classification system, resolve generic boundaries of polyphyletic genera and species complexes, as well as establish asexual-sexual links. Nevertheless, most of genera lack sequence data, thus, morphology based identification is still important when introducing new genera or species. In this paper we illustrate, describe, and provide taxonomic notes for 235 dematiaceous coelomycetous genera, including five new genera viz. Apiculospora, Didymellocamarosporium, Melanocamarosporium, Melnikia and Paulkirkia. Phylogenetic analyses of combined sequence data are provided to show placements of dematiaceous coelomycetes in Dothideomycetes, Leotiomycetes and Sordariomycetes. One-hundred and fifty-two (65 %) of genera have sequence data, thus, their taxonomic placement in a natural classification system, is listed as an outline. However, 83 genera still lack sequence data, hence, they are treated as Ascomycota, genera incertae sedis. In addition, separate analyses are provided where better taxonomic resolution is needed.

Taxonomy and phylogeny of dematiaceous coelomycetes

Bunt and smut diseases of wheat: Concepts and methods of disease management

A review is presented of the nutritional requirements and physiology of actinomycetes, with special emphasis on: (a) selective isolation of unusual forms; (b) colonial morphogenesis and induction of sporulation; (c) biosynthesis of secondary metabolites of value, with particular reference to antibiotics and industrial enzymes. The future potential of actinomycetes as major contributors of useful bioactive metabolites is also indicated.

Physiology and nutritional aspects of actinomycetes: an overview

A. rabiei infected 70% of C. arietinum samples from C. Anatolia, Turkey. The standard blotter method, using 5 seeds/Petri dish and 12 h NUV 12 h darkness cycles at 22 deg C, proved most suitable for detecting the fungus. The inoculum was spore contamination and mycelium occurred in the seed coat alone or in seed coat and embryo. Pycnidia were observed only in the seed coat of seeds having deep lesions. Inter- and intracellular mycelium was localized to lesions. Pycnidia were subepidermal and contained mature spores. Pycnidiospores obtained from the seed surface and pycnidia from 14-month-old seed stored at 3 plus or minus 2 deg showed 33% germination. The light and temp. responses of the fungus on PDA revealed that opt. colony growth occurred at 19 deg . Pycnidial formation was max. under NUV but failed in darkness. Both superficial and deep infections were equally potent in the transmission of the disease. The fungus was highly pathogenic to seed and 40-day-old plants.This paper was presented at the 17th Int. Seed Testing Congress 1974.

Detection and location of seed-borne inoculum of Ascochyta rabiei and its transmission in chickpea (Cicer arietinum).

Myrothecium leucotrichum in cowpea, M. roridum in dahlia and nasturtium, and M. verrucaria in soybean and rice were found to be seed-borne for the first time. These are new records on their respective hosts, and their pathogenicity was confirmed. M. leucotrichum was the most virulent species, whereas M. roridum was moderate and M. verrucaria moderate to weakly virulent. Amongst the hosts tested, nasturtium was highly susceptible while pepper was immune to most isolates of the three species. The effect of culture filtrates decreased in order of virulence. M. leucotrichum also produced a toxin. On seed, sporodochia of M. leucotrichum were surrounded by long white setae, while in the other two species, sporodochia had a peripheral thick, wavy band of white mycelium and setae were absent. M. verrucaria was distinguished from M. roridum by small, white contorted hyphae protruding from the sporodochia.

Seed-borne species of Myrothecium and their pathogenic potential

Procedures for detecting seed-borne inoculum of Sclerospora graminicola in pearl millet (Pennisetum typhoides).

Sclerospora graminicola (Sacc.) Schroet. inoculum may be present in pearl millet seed either as oospores externally or in the form of dormant mycelium internally. Oospore inoculum was detected by using the washing method, and mycelial infection by the modified embryo count procedure. Fifty-nine seed samples out of ninety-three obtained from different sources were found contaminated with oospores whose viability was checked by the tetrazolium test. Percentage of viable spores ranged from 5.5 to 20.2. Forty-three samples showed mycelial infection of 0.1–7.5 Per cent in various parts of the seed. Seeds from healthy-looking plants are not necessarily pathogen-free. Transmission was obtained from a two-year-old seed sample contaminated with oospores and from mycelium. The significance of the results with particular reference to survival of inocula, development of epidemics and quarantine implications in international movement of germplasm are discussed.

Sclerospora graminicola in pearl millet seeds and its transmission

Alternaria sesami, A. sesamicola, A. tenuis, and A. longissima were detected in Korean seed samples of Sesamum indicum L. A. sesamicola was the predominant species, seed infection in some samples ranging between 30 and 68%. A. sesami and A. longissima were recorded only in low percentages of 1–3. Detailed descriptions are given on the habit characters of the four species and on the morphology of conidia, supported by photographs and diagrammatic sketches. Based on the original descriptions and the isolates studied it is concluded that A. sesami and A. sesamicola are two distinct species. A. longissima generally regarded as a saprophyte, was for the first time found to be a pathogen producing zonate leaf spot, foliage blight, stem necrosis, and spots on capsules of Sesamum indicum. A. sesami and A. sesamicola caused severe symptoms; seed germination and seedling stand was adversely affected.

Paul Neergaard

Papers

Detection and location of seed-borne inoculum of Ascochyta rabiei and its transmission in chickpea (Cicer arietinum).

Seed-borne species of Myrothecium and their pathogenic potential

Procedures for detecting seed-borne inoculum of Sclerospora graminicola in pearl millet (Pennisetum typhoides).

Sclerospora graminicola in pearl millet seeds and its transmission

Taxonomy and pathogenicity of four seed-borne species of Alternaria from sesame