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Introduction
Rice (Oryza sativa L.) is the staple cereal in the diet of about 2 billion people in the world (Ziska et al. 2015). Brazil is the largest rice-producing country outside of Asia, and in the 2019 to 2020 season, it produced 11.16 billion kg in an area of 1.6 million ha (CONAB 2020). In the 2019 to 2020 season, the Rio Grande do Sul (RS) and Santa Catarina (SC) states accounted for more than 80% of Brazilian rice production, producing 8.2 billion kg of rice in the flooding system (CONAB 2020). The rice crop in RS and SC is characterized by permanent flood irrigation, allowing these areas to produce very high yields (SOSBAI 2018).
One of the most important factors limiting rice yield is weed infestation, especially weedy rice (WR) (Oryza spp.) (Ziska et al. 2015). WR can reduce rice grain yield by more than 70% (Dai et al. 2014; Singh et al. 2017) if uncontrolled. Weedy rice is very competitive, because it is morphophysiologically similar to rice, as both plants belong to the same genus and species (Fontana et al. 2007; Kraehmer et al. 2016). WR populations infesting rice fields in southern Brazil have high phenotypic and genotypic variability (Kalsing et al. 2019; Roso et al. 2010) just like those in other regions of the world (Shivrain et al. 2010; Wongtamee et al. 2017). However, in most rice fields, WR-predominant populations are taller, have low tillering capacity, and have shorter and thicker grains than commercial rice cultivars (Fleck et al. 2008). WR populations usually have high seed-shattering capability and seed dormancy (Nunes et al. 2015), usually have seeds with a pigmented pericarp, and have a high tolerance to stressors (drought and cold) (Bevilacqua et al. 2015; Dai et al. 2017; Piveta et al. 2021; Zhao et al. 2020). Due to its botanical similarity with cultivated rice, WR is difficult to control chemically and culturally (Fontana et al. 2007).
Thus far, the most effective alternative for the selective control of WR in the rice crops has been the ClearfieldTM rice (CL) system, which includes the use of imidazolinone (IMI) herbicides in IMI-resistant rice cultivars (Fruet et al. 2020), initially marketed in the United States in 2002 (Burgos et al. 2008)...