CONICET | Buscador de Institutos y Recursos Humanos

This study aimed to establish the physiological bases of glyphosate resistance in the recently evolved glyphosate resistant Sorghum halepense populations originated from cropping systems of Argentina. Several experiments were conducted to evaluate 14C-glyphosate leaf absorption and translocation in two glyphosate-resistant (R) and one susceptible (S) S. halepense populations collected in the field. At the four-leaf stage, one drop (1µL) of radio-labeled glyphosate treatment solution [25 mM glyphosate containing 0.53 kBq [14C]-glyphosate ([14C]-phosphonomethyl)] was applied to the midpoint of the upper surface of the fourth fully expanded leaf. Percentages of 14C-glyphosate leaf absorption and translocation to different plant organs (treated leaf, untreated leaves, stem and roots) were estimated after glyphosate exposure. One of the S. halepense R populations consistently showed reduced glyphosate leaf absorption (20%) compared to the S population (35%). Individuals of both R populations exhibited altered glyphosate translocation patterns. The R plants when compared to S plants showed significantly less glyphosate translocation to roots (8% vs. 30%) and stems (4% vs. 24%). A notably higher proportion of the applied glyphosate remained in the treated leaves of R plants (66%) than in treated leaves of S plants (29%). Our results indicate reduced glyphosate leaf absorption and translocation as the primary mechanisms endowing glyphosate resistance in these S. halepense populations.