DNA‐based detection and quantification of Ascochyta rabiei in chickpea (Cicer arietinum) using droplet digital PCR

Abstract

Ascochyta blight (AB) disease, caused by the fungal pathogen Ascochyta rabiei, is a major production constraint in many chickpea‐growing regions worldwide, causing substantial reductions in grain yield and seed quality. The management of AB is challenging due to limited genetic resistance and the evolving aggressiveness of A. rabiei. Currently, there is a heavy reliance on visual assessment by expert pathologists for the detection and quantification of disease severity, and limited ability to impartially quantify pathogen growth and inoculum potential in the field. In this study, we address these gaps by developing a single‐copy genetic marker for the sensitive detection and quantification of A. rabiei mycelium and conidiospores. Using a droplet digital PCR (ddPCR) assay, our method provides a sensitive (≤5 × 10−2 pg DNA, 1 gene copy) approach to assess A. rabiei biomass throughout its lifecycle on living and dead plant tissues. The method (i) has specificity to A. rabiei in diseased plant samples; (ii) discriminates among chickpea cultivars with varying AB resistance prior to the onset of visible symptoms; (iii) detects differences in primary A. rabiei conidiospore inoculum load from field‐grown chickpea stubble; and (iv) has potential application to disease management, breeding and epidemiology.