In vitro expression of variation of glyphosate tolerance in Sorghum halepense

The in vitro response of five different Sorghum halepense biotypes against the non-selective, broad-spectrum herbicide glyphosate was assessed. Seeds from donor plants (collected in various sites all over Greece) were aseptic ally germinated on a hormone-free liquid Murashige and Skoog (MS) medium an d emerging plantlets were inoculated on a solid MS medium supplemented with 13.6 mu M 2.4-dichlorophenoxyacetic acid and 4.6 mu M kinetin for callus i nduction. Exponentially growing calli were initially subcultured twice on i nduction medium and then transferred to a selection medium containing 10(-3 ) M or 10(-4) M (a.i.) glyphosate, The fresh weight of the cultured calli a nd the callus viability (expressed as callus dehydrogenase activity) were r educed as glyphosate concentration increased, Significant differences were observed among different biotypes. Regenerated plantlets were submitted to a conventional evaluation for glyphosate tolerance. The observed in vitro r esponse of S. halepense to glyphosate was directly related to the in vivo h erbicide tolerance observed both on donor and on regenerant plants.