First Case of Conyza canadensis from Hungary with Multiple Resistance to Glyphosate and Flazasulfuron
Palma-Bautista, Candelario; Tahmasebi, Behroz Khalil; Fernández Moreno, Pablo Tomás; Rojano Delgado, Antonia M.; Alcántara-de la Cruz, Ricardo; Prado Amián, Rafael de
Conyza canadensis is a species invading large areas throughout the world, mainly due to its
ability to evolve herbicide resistance. In Hungary, extensive areas have been infested by this species
due to the difficulty in controlling it with glyphosate. To determine whether poor control was a
result of misapplication or glyphosate resistance, eight suspected glyphosate-resistant C. canadensis
populations from different Hungarian regions were studied. In whole-plant dose-response assays
with glyphosate, the LD50 and GR50 values (survival and fresh weight reduction at 50% relative
to the untreated control, respectively) indicated that resistance was confirmed in five of the eight
populations (H-5 population being the most resistant). Additionally, the shikimic acid accumulation
tests corroborated the results observed in the dose–response assays. 11 alternative herbicides from six
different modes of action (MOA) were applied at field doses as control alternatives on populations
H-5 and H-6 (both in the same regions). The H-5 population showed an unexpected resistance to
flazasulfuron (ALS-inhibitor). The ALS enzyme activity studies indicated that the I50 for H-5 with
flazasulfuron was 63.3 times higher compared to its correspondent susceptible population (H-6).
Therefore, the H-5 population exhibited multiple-resistance to flazasulfuron and glyphosate, being
the first case reported in Europe for these two MOA.
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