Water Limitation Causes Early-Stage Metabolic Perturbation in the Interaction of Soybean and Asian Soybean Rust

Soybean is a valuable commodity, and its production has been menaced by more frequent drought events and Asian soybean rust, caused by Phakopsora pachyrhizi. This study compared the leaf metabolic profile of soybean plants exposed or not to controlled water limitation and then infected with rust at the beginning of fungal colonization. Disease severity was enhanced in plants grown with water limitation, which also had contrasting metabolic profiles compared with those with regular irrigation. Water limitation associated with disease increased defense-related compounds at both 12 and 24 h after inoculation. Naringenin and daidzein, among other flavonoids, accumulated more in inoculated plants, even more so when soybeans were grown in water limitation. Amino acid concentration was negatively correlated with water limitation, which could compromise plant immunity and explain why plants with a stress combination had higher disease severity. The results help us to understand the complex interaction between drought and disease severity, a condition found in the tropics.