Investigating the molecular detection of seed-borne Ascochyta rabiei in chickpeas, its transmission to seedlings, and the impact of intercropping on Ascochyta blight spread, severity, and chickpea yield

Abstract

Montana is currently the leading producer of chickpeas in the United States; however, chickpea (Cicer arietinum L.) production faces a significant threat from Ascochyta rabiei, the causal agent of Ascochyta blight (AB). AB is a devastating seed-borne and stubble-borne disease that results in severe yield losses worldwide. The polycyclic nature of the disease complicates management efforts, due to airborne and rain-driven spores, as well as infected seeds, which can serve as primary inoculum sources, facilitating both local and international disease dissemination. Thus, this dissertation studied multiple aspects of A. rabiei dissemination and management, integrating molecular detection methods, host resistance, fungicide treatments, and intercropping strategies to reduce AB's impact on chickpea production. In the first study, a real-time quantitative PCR (qPCR) assay was developed for the detection and quantification of A. rabiei in chickpea seeds and roto rod samples. The assay demonstrated specificity and high sensitivity (as low as 10 femtograms), which offers a valuable complementary tool to seed health tests and early disease detection in seeds. However, a more robust assay is required to accurately quantify the pathogen from roto-rod samples. The second study focused on evaluating the effectiveness of host resistance, fungicide seed treatments, and surface sterilization in controlling A. rabiei transmission from seeds to seedlings. The results showed significant differences across treatments, highlighting the role of genetic resistance and chemical seed treatments in reducing pathogen transmission rates and improving seedling establishment. The third study investigated the impact of chickpea-flax intercropping on A. rabiei dispersal, disease severity, chickpea yield, and canopy microclimatic conditions. Field trials across multiple locations and years showed that intercropping reduced disease spread and severity, likely by modifying canopy microclimate through increased temperature and lower relative humidity and leaf wetness duration (LWD). These modifications seem to be affected by cultivar and year. Genetic resistance further reduced disease incidence, while intercropping required fewer fungicide applications for effective control. However, intercropping significantly penalized chickpea and flax yields. Overall, these studies advance current knowledge on A. rabiei detection, transmission, and management, offering practical recommendations to enhance AB management in chickpeas and ensure sustainable production.