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Abstract
Abstract: The objective of this work was to evaluate the distribution of imidazolinone-resistant (IMI-R) red rice (Oryza sativa) populations, the frequency of alleles conferring resistance to IMI, and the adoption of agronomic practices applied to red rice control, across growing seasons and production regions of the state of Rio Grande do Sul (RS), Brazil. In the experiment, 1,008 red rice populations were screened for resistance to IMI, 760 IMI-R red rice plants were genotyped for the acetolactate synthase (ALS) alleles conferring resistance to IMI, and 40 'Clearfield' rice growers were surveyed. IMI-R red rice populations were widespread throughout RS since the 2006/2007 growing season, with a higher initial frequency in the Depressão Central and Fronteira Sul production regions. The occurrence of IMI-R red rice ranged from 1.6 to 3.5 years after 'Clearfield' rice release. Gly654Glu was the most frequent ALS mutation in IMI-R red rice populations, which shows a gene flow from the most used 'Clearfield' rice cultivars to the red rice plants. Crop rotation systems and certified seed were used by only 30% of the surveyed growers of 'Clearfield' rice, with lower percentages in the production regions where IMI-R red rice appeared faster.
Highlights
Red rice is one of the most damaging weeds of rice cultivations in several regions of the world (DurandMorat et al, 2018)
Red rice control, combined with better fertilizer practices and sowing time, have increased the average grain yield of CL rice by 2 Mg ha-1 in Southern Brazil (Roso et al, 2010). These benefits have encouraged the use of this technology continuously and, as a consequence, imidazolinone-resistant (IMI-R) red rice was identified in commercial rice fields just a few seasons after CL rice was released in the USA (Zhang et al, 2006; Ellstrand, 2018), Brazil (Menezes et al, 2009), Italy (Busconi et al, 2012), and other regions of Europe and Latin America (Ziska et al, 2015)
The percentage of IMI-R red rice varied between production regions, and it was higher in the Depressão Central and Fronteira Sul, in comparison to the other production regions
Summary
Red rice is one of the most damaging weeds of rice cultivations in several regions of the world (DurandMorat et al, 2018). Red rice control, combined with better fertilizer practices and sowing time, have increased the average grain yield of CL rice by 2 Mg ha-1 in Southern Brazil (Roso et al, 2010). These benefits have encouraged the use of this technology continuously and, as a consequence, imidazolinone-resistant (IMI-R) red rice was identified in commercial rice fields just a few seasons after CL rice was released in the USA (Zhang et al, 2006; Ellstrand, 2018), Brazil (Menezes et al, 2009), Italy (Busconi et al, 2012), and other regions of Europe and Latin America (Ziska et al, 2015). In addition to the herbicide selection pressure, the gene flow from CL rice to red rice escapees has contributed to the IMI-R red rice evolution (Goulart et al, 2012; Bzour et al, 2018)
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