Paraquat tolerant Lolium perenne L.: effects of paraquat on germinating seedlings

A cultivar of Lolium perenne L. (Causeway) selected for tolerance to foliar-applied paraquat was shown also to be tolerant at seed germination and establishment. When seeds were germinated in paraquat solutions (1, 3, 9, 27 ppm), Causeway was more than ten times as tolerant as a normal cultivar of L. perenne. When germination and survival were studied in a soil which had been sprayed with paraquat (0.0, 0.3, 0.9, 2.7 kg/ha) before sowing, Causeway was nearly three times as tolerant as a normal cultivar. Holcus lanatus L. was about equal to normal L. perenne, but Poa trivialis L. was less tolerant. Phytotoxicity was greater in a 10.5% organic than a 4.8% organic soil. It is concluded that the mechanism of paraquat tolerance operates in the non-photosynthetic tissues of germinating seedlings as well as in the photosynthetic tissues of older plants, although the degree of tolerance varies according to the mode and stage of application of the herbicide. There might be advantages in using a paraquat tolerant cultivar of L. perenne when direct drilling grass after sward destruction by paraquat.