Response to glyphosate and electrophoretic variation of Cynodon dactylon (L) Pers populations

Response to glyphosate and isozyme variation were investigated in eight populations of Cynodon dactylon (L) Pers (var dactylon ) selected from 58 native populations from Italy. Morphological and phenological observations allowed the identification of four populations as temperate biotypes and the remaining four populations as seleucidus biotypes. No populations were resistant to the recommended dose of glyphosate (3600 g AE ha −1 ). At the sublethal doses of 1800, 900 + 900 and 450 + 450 g AE ha −1 , seleucidus accessions were 8.6, 2.7 and 3.4 times more tolerant than temperate accessions, respectively. Electrophoretic patterns of seven enzyme systems evidenced a total of 34 bands and 28 phenotypes across the eight populations. Isozyme variation between populations contributed the major proportion of total diversity of the variable detected isozymes, while the contribution of within‐population variation was negligible. Total phenotypic variation was in agreement with values reported for cosmopolitan and geographically widespread species. The low levels of within‐population diversity match the predominantly asexual reproduction strategy of the populations examined. Classification and ordination techniques revealed that the different genetic structures of seleucidus and temperate populations are associated with distinct responses to sublethal doses of glyphosate. The results confirmed the presence of an association between morphometric and isozyme variability in the populations of C dactylon . The role of monitoring perennial weeds to evaluate the agricultural impact of the introduction of genetically engineered crops with novel traits such as resistance to glyphosate is discussed. © 2000 Society of Chemical Industry