An accession of velvetleaf (Abutilon theophrasti Medik. # ABUTH) known to be highly tolerant of atrazine [6-chloro-N-ethyl-N-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and a normal susceptible accession were crossed reciprocally. F1 plants were intermediate in response to atrazine, but they were more like the tolerant parent than the susceptible parent. The response of F1 plants was the same for each reciprocal cross, indicating that atrazine tolerance was not cytoplasmically inherited. Response of F2 plants to atrazine was consistent with a ratio of one tolerant: two intermediate: one susceptible. These results and further evaluations of F3 plants indicated that atrazine tolerance was controlled by a single, partially dominant gene.
