Early Detection of Airborne Inoculum of Magnaporthe oryzae in Turfgrass Fields Using a Quantitative LAMP Assay

Gray leaf spot (GLS) is a destructive disease of perennial ryegrass caused by a host specific pathotype of the ascomycete Magnaporthe oryzae. Early diagnosis is crucial for effective disease management and the implementation of Integrated Pest Management practices. However, a rapid protocol for the detection of low levels of airborne inoculum is still missing. We developed a pathogen-specific quantitative loop-mediated isothermal amplification (qLAMP) assay coupled with a spore trap system for rapid detection and quantification of airborne inoculum of the M. oryzae perennial ryegrass pathotype, and tested its suitability for implementation in GLS-infected turfgrass fields. In summer 2015, two perennial ryegrass plots were artificially inoculated with the pathogen, with four continuously running custom impaction spore traps placed in each plot. Sampling units were replaced daily and tested with the developed qLAMP assay, while plots were monitored for symptom development. Results confirmed that the qLAMP assay-trap system was able to detect as few as 10 conidia up to 12 days before symptoms developed in the field. LAMP technology is particularly appropriate for field implementation by nontechnical users, and has the potential to be a powerful decision support tool to guide timing of fungicide applications for GLS management.