Drought and Herbivory Differentially Modulate the Leaf Exudation of Organic Acids in Chickpea

Drought and herbivory challenge chickpea growth and yield. Consequently, we designed two glasshouse experiments to investigate the effects of drought and herbivory on chickpea growth and defence and explored the trade-offs between exudation of organic acids and growth. Experiment 1 combined factorially twelve varieties and three water regimes. Experiment 2 combined factorially six cultivars, two water regimes, and two herbivory treatments - plants challenged with Helicoverpa armigera larvae and untreated controls. Drought decreased the amount of leaf exudates by 71% and growth traits by 15 to 48%. Herbivory increased the amount of leaf exudates by 60% and reduced shoot biomass by 32% in well-watered plants, and increased exudates by 49% and reduced shoot biomass by 38% under severe water stress. Leaf damage, and survival and size of Helicoverpa armigera larvae were larger in water-stressed plants, and correlated negatively with the leaf exudates in both water regimes. Our study did not support a trade-off between growth and defence: in experiment 1, there was no trade-off between exudates and growth traits in 25 out of 27 cases resulting from the combination of nine traits and three water regimes; weak trade-offs in 2 out of 27 cases were apparent under water stress; in experiment 2, growth and exudates were unrelated. The complex relationship between drought, herbivory, and plant defence underscores the need for a nuanced understanding of crop management.