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Maximum quantum yield of photosystem II (Fv/Fm) after application of paraquat at 105 (triangle up), 420 (circle), 840 (triangle down) and 3360 g a.i. ha-1 (square) to paraquat-resistant (PRHC, solid, red lines) and -susceptible (S, dashed, black lines) Lolium perenne L. spp. multiflorum. Data points are means (N = 8) and bars represent standard errors.
