Abstract
This paper reports the first C. radiata population with resistance to glyphosate and multiple resistance to the acetolactate synthase (ALS) inhibitor, imazamox. Two populations, one putative resistant (R) and one susceptible (S), were used in the studies. Dose–response experiments were performed to evaluate the resistance factor (RF). Shikimic acid accumulation, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) and ALS enzyme activities were studied together with chemical integrated weed management (adjuvants and alternative herbicides). The resistance to glyphosate and imazamox was confirmed based on the dry weight reduction, visual evaluation and survival. The results of dose–response curve assays showed for the R population intermedium RF for glyphosate (5.1 and 9.7 for amount of herbicide needed to reduce the dry weight by 50% GR50 and lethal dose of 50% LD50, respectively) and high RF for imazamox (34.9 and 37.4, respectively). The low shikimic acid accumulation in R population confirmed the glyphosate resistance. The glyphosate concentration which inhibited the EPSPS enzyme in 50% (I50) was approximately 20 times higher for R population than the S population, while the imazamox I50 in ALS enzyme for the R plants was 89 times greater than the S plants. In the chemical integrated weed management, the foliar retention and effectivity assays showed that the use of adjuvants improves the retention of glyphosate and imazamox, and the reduction in dry weight of weeds. The alternative herbicides study showed that the acetyl-CoA carboxylase (ACCase) inhibitors, paraquat and glufosinate, had better results for control in this species. However, poor control was observed with bispyribac-sodium, metsulfuron-methyl and quinclorac, indicating possible cross-resistance for ALS-inhibitors and also multiple resistance for auxinic herbicides (quinclorac). Nevertheless dose–response experiments are required to confirm this assumption.
Highlights
Cultivated rice is among the most important cereal crops in the world, and plays an essential role in global food security and reduction in poverty [1,2]
For the R population, both herbicides showed dry weight reduction compared to untreated plants higher than 60%, visual evaluation less than 70% and a survival of 100% (Table 2), confirming resistance to glyphosate and imazamox in this species
Chloris radiata is a species that has become a problem in recent years, attributable to possible failures in chemical control
Summary
Cultivated rice is among the most important cereal crops in the world, and plays an essential role in global food security and reduction in poverty [1,2]. For more than half of the world’s population, rice is a staple food, contributing 21% of their daily calorie intake [3]. Rice production has been described as the world’s single most important economic activity [4]. In 2018, world rice production was highly localised. Of the total paddy rice harvested area (167.1 million hectares), India was the primary producer with 27.6%, followed by China (18.2%). In America, Brazil ranks first as the highest producer (30.4%), followed by the United States (19.3%), Colombia (10.4%) and
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