Absorption, translocation and allocation of glyphosate in resistant and susceptible Chilean biotypes of Lolium multiflorum

Glyphosate [N‐(phosphonomethyl) glycine] is currently the most important non‐selective, wide‐spectrum herbicide used worldwide. Introduced in 1974, glyphosate was initially a non‐crop herbicide and plantation crop herbicide, although it is now widely used in no‐till crop production and, more recently, for weed control in herbicide‐resistant transgenic crops, such as maize, soybean and cotton ( Baylis 2000 ; Caseley & Copping 2000 ). Despite its widespread and long‐term use, no case of evolved resistance to glyphosate was documented until 1996 ( Pratley et al . 1996 ). Since then, a few other cases have been reported. To date, evolved resistance to glyphosate has been identified and documented in Lollium rigidum in Australia ( Powles et al . 1998 ; Pratley et al . 1999 ), Eleusine indica in Malaysia ( Lee & Ngim 2000 ), and L. rigidum in South Africa and California (USA), and Conyzia canadensis in Delawere (USA) ( Van Gessel 2001 ). Also, accessions of L. rigidum from South Africa and California have been reported to resist glyphosate ( Heap 2001 ). In Chile, the first case of glyphosate‐resistance in Lolium multiflorum was reported in 1999 and documented in 2003 ( Pérez & Kogan 2003 ). This case was the result of an intensive selection pressure caused by the continuous applications of glyphosate in fruit orchards over 8–10 years. The present study is a first approach to elucidating the mechanism involved in the resistance of one biotype of L. multiflorum selected in Chilean orchards.