Changes in leaf blade morphology and anatomy caused by clomazone and saflufenacil in Setaria viridis, a model C4 plant

Clomazone and saflufenacil are herbicides extensively used worldwide to weed control. We studied the effects of these two herbicides on morphoanatomical parameters of Setaria viridis. Plants were sprayed with four concentrations of each herbicide (clomazone: 500, 1000, 1500 and 2000 g of active ingredient (ai) ha−1 and saflufenacil: 49, 98, 147 and 196 g ai ha−1) besides control (without spraying) 20 days after transplantation. The experimental design was completely randomized with five replicates per treatment. Pigment content, visible injuries, morphological and ultrastructural changes were evaluated. No signs of tolerance to either of the tested herbicides were observed. Clomazone caused a decrease in photosynthetic pigment content over time, mostly in young leaves, leading to an “albino” like appearance. There was a reduction in the number of grana in the chloroplasts of mesophyll cells (MC) in necrotic areas. Saflufenacil reduced chlorophyll content, impairing energy absorption in the antenna complex. Injuries to foliar tissues, such as necrosis and depigmentation, were visible as early as 24 h after herbicide application. Bundle sheath chloroplasts (BSC) and MC were completely deformed. The data support the use of S. viridis as a model plant for studies on herbicide effects in C4 monocots.