Combined effects of drought and simulated pathogen attack on root exudation rates of tomatoes.

Background and aims: Food production is threatened by direct climate change effects including drought. Indirect effects, including changes in plant-pathogen dynamics and increased susceptibility to pathogens, further exacerbate the risks. Root exudation, which plays a crucial role in plant defence against drought and pathogens, is influenced by both water stress and pathogens. However, the interactive effects of these abiotic and biotic factors are rarely studied. Methods: We conducted a controlled environment experiment to investigate the effects of moderate drought and simulated pathogen attack (using pipecolic acid, an inducer of systemic acquired resistance) on the rates of root exudation of total organic carbon (TOC) and total nitrogen (TN) of four tomato cultivars grown in potting soil. Results: Drought increased the exudation of TOC and TN per unit of root area, while pipecolic acid did not have any significant effect. Furthermore, there was no interaction observed between the abiotic and biotic factors. However, due to the reduction in plant and root biomass caused by drought, the total exudation per plant remained similar between control and water-limited plants. Additionally, pipecolic acid reduced the carbon-to-nitrogen ratio of exudates and increased the total exudation of TN. Conclusion: The increased exudation observed in drought-stressed plants may serve as a strategy to maintain root and rhizosphere activity despite reduced root growth. Notably, the impact of drought differed among the tested cultivars, highlighting their diverse levels of drought tolerance. This emphasises the importance of preserving a wide range of crop cultivars to ensure food security under increasing drought. [ABSTRACT FROM AUTHOR]