Drought tolerance is a complex trait in plants that involves different biochemical mechanisms. During two years of study (2019–2020), the responses of 64 arugula genotypes to drought stress were evaluated in a randomized complete block design with three replications under field conditions. Several metabolic traits were evaluated, i.e. relative water content, photosynthetic pigments (chlorophyll and carotenoids), proline, malondialdehyde, enzymatic antioxidants (catalase, ascorbate peroxidase, and peroxidase), total phenolic and flavonoid contents and seed yield. On average, the drought stress significantly increased the proline content (24%), catalase (42%), peroxidase (60%) and malondialdehyde activities (116%) over the two years of study. As a result of the drought stress, the seed yield (18%), relative water content (19.5%) and amount of photosynthetic pigments (chlorophyll and carotenoids) dropped significantly. However, the total phenolic and flavonoid contents showed no significant changes. Under drought stress, the highest seed yields were seen in the G50, G57, G54, G55 and G60 genotypes, while the lowest value was observed in the G16 genotype (94 g plant−1). According to the findings, when compared to the drought-sensitive genotypes, the drought-tolerant arugula genotypes were marked with higher levels of proline accumulation and antioxidant enzyme activity. Correlation analysis indicated the positive effects of peroxidase, catalase and proline on seed yield under drought conditions. These traits can be considered for the selection of drought-tolerant genotypes in breeding programs.

Supplemental materialTable S1. Soil physicochemical characteristics of a field experiment over two years of study. Table S2. Monthly mean minimum and maximum air temperatures, total rainfall and evaporation during the growing seasons (2019 and 2020). Years 2019 2020 Tmin (°C) T max (°C) Loam -clay soil Soil texture 3.02 Electrical conductivity of soil (ds/m) 7.9 pH 0.074 Nitrogen (%) 18.6 Absorbable phosphorus (mg/kg soil) 146 Absorbable potassium (mg/kg soil) 9.4 Iron (mg/kg soil) 3.8 Zinc (mg/kg soil)