Bioassays for Diagnosis of Resistance to the Herbicides Imidazolinones in Rice Plants

Red rice is the most troublesome weed in rice paddy fields. Herbicide resistant rice cultivars allow red rice control through the herbicides imidazolinones. However, imidazolinone resistant red rice biotypes have occurred in several rice paddy fields. The aim of this study was to develop rapid methods to identify imidazolinone resistant rice plants at different stages of rice plant development. The rice cultivars IRGA 422 CL, SATOR CL and PUITA INTA CL were used as well-known resistant cultivars, and IRGA 417 as a well-known susceptible check. The seed, seedling, and tiller bioassays discriminated resistant and susceptible plants efficiently, being considered fast methods for herbicide resistance diagnosis in rice. The discriminatory concentrations between resistant and susceptible plants to the herbicides imazethapyr + imazapic for the seed, seedling and tiller bioassays were 0.01 mM, 4 mM and 3 mM, respectively. The use of these bioassays allows the identification of resistant individuals even during the rice crop season, and can be used to indicate the need of alternative measures to maintain the sustainability of red rice control in fields cultivated with herbicide resistance cultivars.