Sensibility to AHAS inhibitors in progenies of wild Helianthus annuus hybridized to a CL sunflower cultivar

PRESOTTO, ALEJANDRO; GIGÓN, RAMÓN; RENZI, JUAN PABLO; POVERENE, MÓNICA; CANTAMUTTO, MIGUEL

Congreso; 18th International Sunflower Conference; 2012

Acetohidroxyacid synthase (AHAS) inhibitors are worldwide used because of their broad weed control spectrum, high selectivity, low application doses and low mammalian toxicity. Resistance to AHAS inhibitors has been incorporated into several crops through conventional breeding, to develop the Clearfield® technology (CL) currently available in corn, rapeseed, rice, wheat, and sunflower. As the invader wild H. annuus hybridizes with sunflower in central Argentina, the occurrence of imidazolinone resistant wild-crop hybrids is possible. This work studied the sensitivity to sulfonylureas and imidazolinones herbicides in the progeny (F1) between an imazapyr (IMI)-resistant sunflower cultivar and wild sunflower populations. Three biotypes (IMI, F1 and WILD) were grown in the glasshouse up to 2-4 leaf stage. Plants were sprayed at 0, 0.5 and 2x of the commercial herbicide dose. The herbicide evaluation included five sulfonylureas and two imidazolinones. Phytotoxicity was estimated by a visual scale and measure of dry aerial biomass. The WILD did not show any herbicide resistance, and mortality was over 93% with all the herbicides and dose combinations. IMI and F1 plants had higher tolerance to imidazolinones than to sulfonylureas. Imazapyr did not affect survival of the F1 progeny, even at 2x dose. In contrast, 0.5x imazethapyr did not affect IMI plant survival, but killed more than 50% F1 plants.These results demonstrated the high susceptibility of wild H. annuus biotypes to AHAS herbicides and that the hybridization of wild H. annuus with an IMI sunflower cultivar increased the tolerance to imazapyr and imazethapyr. Sunflower volunteers and crop-wild hybrids would not be controlled by the recommended doses of imazapyr or imazethapyr, and could become dangerous weeds in IMI sunflower and corn fields. The incorporation of imidazolinone tolerance in crops is a valuable technology for weed management, however it should include crop rotation and to alternate or combine the usage of these herbicides with others which have different modes of action to promote greater efficiency and durability of this technology.This study reported the feasibility of transfer the imidazolinone resistance to wild-crop hybrids and the consequent risk if Clearfield technology were used without the development of integrated weed management strategies.