An Improved Detached-Leaf Assay for Phenotyping Net Blotch of Barley Caused by Pyrenophora teres

Net blotch, caused by Pyrenophora teres, is a major barley (Hordeum vulgare) leaf disease worldwide. P. teres occurs as two forms-P. teres f. teres, and P. teres f. maculata-inducing net and spot-like symptoms, respectively. An intact-seedling assay, where entire seedlings are inoculated by spraying with a conidial suspension, is frequently used for phenotyping net blotch. However, this presents a biosecurity risk in the glasshouse when nonlocal isolates are being screened. Alternatively, a detached-leaf assay (DLA-droplet method) can be used in which leaf segments laid out in a covered tray are inoculated with droplets of a conidial suspension, confining the inoculum. However, using this method, net and spot form symptoms cannot be distinguished from each other. We have developed an improved DLA (DLA-spray method) in which detached whole leaves are sprayed with the inoculum to produce distinct lesions. We compare the results for the three phenotyping methods above using four isolates from both net and spot forms of the disease to inoculate a standard set of eight barley genotypes. Results indicate that the DLA-spray method is a functional, informative and rapid test that readily differentiates the two forms of the pathogen in a biosecure environment.