Ascochyta rabiei: A threat to global chickpea production

Abstract

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...

Genome and Transcriptome Analysis of Ascochyta pisi Provides Insights into the Pathogenesis of Ascochyta Blight of Pea

“…To penetrate plant cell walls and use host components for their growth, pathogenic fungi secrete diverse CAZymes during infection. A. rabiei secretes cutinase, xylanase, and pectinase to degrade the host barrier ( 36 ). In agreement with this, a total of 555 putative CAZymes were predicted in A. pisi , and 44% of the total CAZymes were constantly increased with the development of infection, suggesting that CAZymes facilitate fungal infection and host colonization and that the function of CAZymes is highly conserved in pathogenic fungi.…”

Ascochyta Blight in Chickpea: An Update

“…As mentioned above, A. rabiei is responsible for one of the most devastating fungal diseases that affect this crop [ 22 ]. Ascochyta blight was first identified in 1911, in what was then India’s North-West Frontier Province (currently Pakistan) [ 25 ]. Since then, it has spread to most chickpea-growing areas around the world, including 40 countries in western Asia, southern Europe, northern Africa, certain countries in the Americas, and parts of Oceania [ 25 ].…”

“…Ascochyta blight was first identified in 1911, in what was then India’s North-West Frontier Province (currently Pakistan) [ 25 ]. Since then, it has spread to most chickpea-growing areas around the world, including 40 countries in western Asia, southern Europe, northern Africa, certain countries in the Americas, and parts of Oceania [ 25 ]. No cases have been reported in Nepal, Myanmar, Bolivia, Peru, Chile, Colombia, Libya, Malawi, Zambia, Sudan, Uganda, or the Balkans [ 26 ].…”

“…It also has a sexual reproductive stage or teleomorph, known as Didymella rabiei (Kovachevski) v. Arx (also Mycosphaerella rabiei Kovachevski) ( Figure 1 ). The key taxonomic descriptors for this fungus are phylum Ascomycota, class Dothideomycetes, order Pleosporales, family Didymellaceae [ 25 , 29 , 30 ].…”

“…Long periods of cold and humidity are the most propitious for oozing conidia that are spread from pycnidia by the rain [ 31 ]. The persistence of such environmental conditions and the presence of compatible mating types [ 25 ] favor the sexual cycle, which makes it more likely for the disease to turn into an epidemic. The dissemination distance of the different spores is crucial to determine the spread of the disease.…”