Dogs can detect powdery mildew ( Erysiphe necator) in grapevine (Vitis vinifera) leaves

Powdery mildew ( Erysiphe necator, PM) is a fungus that affects grapes ( Vitis spp.) worldwide. Despite its negative impact on vineyard production and economics, there is no fast and economic way to detect it at scale. The aim of this study was to evaluate dogs' capability to detect grape leaves infected with PM. Three pet dogs were trained to perform a detection task using a three-alternative automated olfactometer. In Experiment 1, dogs were trained to alert to the headspace of a vial containing a PM positive leaf (with visible signs of infection in more than 50% of leaf surface area) and discriminate it between control leaves (e.g., healthy) and leaves inoculated with other fungi. Dogs learned the discrimination task and reached sensitivity and specificity values of 0.96 +/- 0.01 (SE). In Experiment 2, we tested dogs' response rate to the filtered (10 mu m) headspace, a gauze exposed to the headspace of a PM positive leaf for 24 h, and to a control leaf after 1 and 24 h post PM inoculation. Response rate to the filtered headspace and to the inoculated gauze were not statistically different from the response rate to the PM positive leaf (0.96 +/- 0.04 SE). The average response rate to leaves right after inoculation and 24 h post inoculation was 0.58 +/- 0.10 (SE). Although when averaged across dogs this was above chance, it indicates that longer than 24 h post inoculation is needed for proficient detection. Experiment 2 results also suggest dogs were detecting PM specific VOCs that were captured by the gauze and passed through the 10 mu m filter, and not to the presence of airborne spores. In Experiment 3, we tested dogs' ability to discriminate between PM ( Erysiphe necator) and a fungus of the same genus ( Erysiphe lagerstroemiae). Our results show that dogs did not spontaneously discriminate between these two fungi, even though they were tested on different hosts. This suggests that these two fungi are perceptually similar to dogs. Our results show that dogs are proficient in detecting and discriminating leaves with PM. Future studies are needed to evaluate their use as PM biosensors in vineyards.