Detection of the dynamic response of cucumber leaves to fusaric acid using thermal imaging.

Fusarium wilt is a major disease that causes severe losses in crop yield. Fusaric acid (FA), a non-specific fungal toxin produced by many Fusarium species, can accelerate the wilting of many crops. Unraveling the role of FA in the wilt process can enrich the understanding of the mechanism of pathogenesis. To investigate the dynamic process of the cucumber's response to FA, we used digital infrared thermography (DIT) to detect leaf temperature during the alternation of light and dark conditions in greenhouse hydroponic experiments. During FA treatment, we found that the leaf temperature of cucumber plants increased when stomata closure was induced by FA. Under the alternation of light and dark, FA-treated plants had a higher leaf temperature in the light and a lower temperature in the dark, when compared to untreated plants. To confirm the uncontrolled water loss was from damaged leaf cells, as a result of FA treatment, and not from the stomata, an experiment was conducted using a split-root system in which spatially separated cucumber roots were each supplied 0 ppm or 100 ppm of FA. In the split-root system, the low temperature areas of the leaves in the dark had a higher FA concentration and more severe membrane injury than the high temperature areas, demonstrating that FA is primary xylem transported. We concluded that membrane injury caused by FA led to non-stomata water loss and, ultimately, to wilting. Combining the response of the leaves under the light and dark conditions with the DIT employed in the present study permitted noninvasive monitoring and direct visualization of wilting development.