Abstract
Florpyrauxifen-benzyl (FPB) is a new class of auxinic herbicide developed for selective weed control in rice. This study aimed to evaluate the effect of environmental conditions, P450 inhibitors, rice cultivar response, and gene expression on FPB selectivity in rice. Field experiments established in a randomized block design showed that rice plant injury due to two FPB rates (30 and 60 g ai ha−1) was affected by planting time and rice stage at herbicide application. The injury was higher at the earliest planting season and more in younger plants (V2) than larger (V6 and R0). However, no yield reduction was detected. Under greenhouse conditions, two dose-response experiments in a randomized block design showed that spraying malathion (1 kg ha−1) before FPB application did not reduce herbicide selectivity. The addition of two P450 inhibitors (dietholate and piperonyl butoxide, 10 g a.i. seed-kg−1 and 4.2 kg ai ha−1, respectively) decreased the doses to cause 50% of plant injury (ED50) and growth reduction (GR50). However, it seems not to compromise crop selectivity. BRS Pampeira cultivar showed lower ED50 and GR50 than IRGA 424 RI. A growth chamber experiment was conducted in a completely randomized design to evaluate the gene expression of rice plants sprayed with FPB (30 and 60 g ai ha−1). Results showed downregulation of OsWAKL21.2, an esterase probably related to bio-activation of FPB-ester. However, no effect was detected on CYP71A21 monooxygenase and OsGSTL transferase, enzymes probably related to FPB degradation. Further research should focus on understanding FBP bio-activation as the selective mechanism.
Highlights
The main biotic factor that decreases the yield and quality of rice are weeds, exhibiting the greatest potential for yield losses globally (34%), which is greater compared to insects (18%) and phytopathogens (15%) [1]
Maximum plant injuries were observed at high doses (60 g ai ha−1), sprayed at V6 for early planting time 7 days after application (DAA) (27.4%), sprayed at V2 for late planting time 14 DAA (34.8%), and sprayed at V2 for medium planting time 21 DAA (34.4%) (Figure 1)
Contrary to Wright et al.’s [36] conclusion, which suggests that there is no dependency of P450 on the degradation of this herbicide in rice, we considered that there could be more interaction of FBP with P450 inhibitors in plants since there have been reported 356 CYP genes encoding P450 enzymes on rice [48]
Summary
The main biotic factor that decreases the yield and quality of rice are weeds (unwanted plants in the field), exhibiting the greatest potential for yield losses globally (34%), which is greater compared to insects (18%) and phytopathogens (15%) [1]. Rice yield loss due to weeds is estimated at around 10% [1]; up to 100% losses have been reported in the absence of control [2]. The most important weeds in rice areas include the weedy rice complex (Oryza sativa L.), the Echinochloa spp. complex (e.g., Echinochloa crus-galli (L.) Beauv., Echinochloa colona (L.) Link., Echinochloa oryzicola Vasinger.), and the Cyperus spp. complex (e.g., Cyperus difformis L., Cyperus esculentus L., Cyperus iria L., Cyperus rotundus L.) among others such as Leptochloa species, Cynodon dactylon (L.) Pers., Eleusine indica (L.) Gaertn., Ischaemum rugosum Salisb., and Paspalum distichum L. The use of synthetic auxin herbicides (SAHs), such as quinclorac and 2,4-D, allowed for the post-emergent selective control of weeds in rice [4,5]. 17 weed-resistant cases to SAHs in rice crop areas have been reported worldwide, limiting the strategies to prevent rice yield losses [6]
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