Differential Responses of Stevia Genotypes to Drought Stress: Implications for Steviol Glycoside Production

Steviol Glycosides (SG) synthesis in Stevia plants is significantly influenced by genetic, climatic, and soil factors. This study evaluates the variations in SG in two Stevia genotypes, ‘Indian’ and ‘Chinese’, under drought stress conditions. Two irrigation levels were employed: a control group receiving 100% field capacity and a drought stress group receiving only 30% field capacity. The study, conducted in 2022 across three farms in Iran—RF1 in Tehran, RF2 in Fars, and RF3 in Golestan—utilized a randomized complete block design, each featuring unique climatic conditions. Our findings indicate that the interaction between research farm, drought stress, and genotype significantly influenced the content of Rebaudioside-A, -B, -C, Stevioside, SG content, SG yield, and leaf yield. The results showed that the highest Reb-A (20.2 mg/g), Stev (55.6 mg/g), and SG content (89.9 mg/g) was observed in RF1. Drought stress had a different effect on the content of various SG compounds in the two genotypes studied, such that drought stress increased the SG compounds in the ‘Indian’ genotype and decreased the average of these compounds in the ‘Chinese’ genotype. Under drought stress, leaf yield decreased in all three research fields and both Stevia genotypes compared to non-stress conditions. The highest yield in all three regions was observed in the ‘Indian’ genotype under non-drought conditions, with yields of 577.0, 881.0, and 1213.0 kg/ha, respectively. Latitude was positively and significantly correlated with Stevioside and Reb-A among the climatic parameters. Altitude and mean annual temperature showed a significant negative correlation with SG metabolites. Drought stress impact on SG content varied by genotype: it increased levels in the ‘Indian’ genotype but decreased them in the ‘Chinese’ genotype. Latitude was positively correlated with SG compounds, while higher altitude and mean annual temperature were linked to reduced SG content. Therefore, cultivating the ‘Indian’ genotype is advisable in regions with lower altitudes, higher rainfall, and moderate temperatures, particularly under water-scarce conditions.