Glyphosate hormesis mitigates the effect of water deficit in safflower (Carthamus tinctorius L.)

BACKGROUND: The current climate change scenario may affect water availability in the soil, impacting the agricultural sector. Planting of safflower (Carthamus tinctorius L.) has increased because of its potential for cultivation under drought conditions during the off-season in Brazil and its high potential for use in biofuel production. There are several reports about the potential of low doses of glyphosate to promote plant growth and development (hormesis). Despite the concept of glyphosate hormesis being well established, little is known about any mitigating effect on plants under water deficit conditions. The hypothesis raised is that low doses of glyphosate promote water stress tolerance during the growth and reproductive phases of C. tinctorius exposed to different water regimes. RESULTS: In regimes with and without water deficiency, growth of plants treated with low doses of glyphosate increased, reaching a maximum stimulus amplitude of similar to 131% of control. However, plants under water deficit required lower doses to achieve maximum growth and development. They maintained photosynthetic rates at the level of well-watered plants because they had reduced stomatal conductance and transpiration. Gains in plant height and leaf area were the same as for controls. CONCLUSIONS: Low doses of glyphosate can act as mitigators of water deficit in C. tinctorius, allowing plants to maintain their metabolism, reaching levels close to those of plants without water stress, as observed for plant height and leaf area. Our findings indicate that there are even greater implications for understanding glyphosate hormesis in plants under drought conditions, given the current climate change scenario. (C) 2020 Society of Chemical Industry