Molecular Diversity of Chickpea Ascochyta Blight Pathogen in Pakistan

Abstract

Ascochyta blight (AB), caused by the necrotrophic fungus Ascochyta rabiei (teleomorph Didymella rabiei), remains the most devastating disease of chickpea (Cicer arietinum L.) in Pakistan, where the crop occupies approximately 2.2 million hectares and serves as a vital source of dietary protein. This comprehensive review synthesizes historical epidemiology, morphological characteristics, pathogenic variability, and molecular diversity of A. rabiei populations in Pakistan. The pathogen exhibits high genetic and pathogenic diversity, driven by factors such as potential historical sexual recombination, high gene flow across regions (particularly in the Thal and Pothwar areas), and strong selection pressure from host resistance genes. Studies using molecular markers including RAPD, SSR, ISSR, and Universal Rice Primers (URP) have revealed extensive polymorphism, distinct genetic clusters, and evidence of long-distance migration, with skewed mating type ratios (predominance of MAT1-2) suggesting limited current sexual reproduction despite signatures of past panmixia. Pathotype classification identifies dominant groups (I–III), with highly aggressive isolates (comparable to international Pathotype IV) emerging in northern regions. Environmental factors (temperature 15–25°C, high humidity, wind dispersal) and agricultural practices (monoculture, seed-borne transmission) exacerbate epidemics, causing yield losses of 10–100%. Advances in QTL mapping, SNP-based GWAS, and host-pathogen interaction studies highlight key genomic regions (on chromosomes Ca2 and Ca4) for durable resistance breeding. Integrated management strategies combining marker-assisted selection, biocontrol agents (Trichoderma), cultural practices, and forecasting models are essential. Continuous molecular surveillance is recommended to anticipate pathogen evolution and safeguard chickpea production in Pakistan.