Seletividade do florpyrauxifen-benzyl ao arroz

Abstract

Florpyrauxifen-benzyl is a new auxinic herbicide developed for selective weed control in rice. Herbicide selectivity in rice can be affected by environmental conditions and crop practices. This thesis aims to evaluate the effect of environmental conditions and P450 inhibitors on florpyrauxifen-benzyl selectivity in rice. In chapter I, field experiments were carried out at the Embrapa Clima Temperado experimental station RS, Brazil in 2019/20 and repeated in 2020/21 growing season, aiming at evaluating the crop injury and yield response of rice to florpyrauxifen-benzyl doses affected by planting time, and growth stage at herbicide application. In chapter II, two doseresponse experiments were carried out under greenhouse conditions at the Federal University of Pelotas, Pelotas RS, Brazil, evaluating the addition of P450 inhibitors and two rice cultivars' responses to florpyrauxifen-benzyl. Lastly, in chapter III, two growth chamber experiments were carried out to evaluate plant injury, and CYP71A21, OsGSTL3, OsGTy, and OsWALK21.2 gene expression of rice plants sprayed with florpyrauxifen-benzyl in variable temperature conditions at the time of application. Rice plant injury due to florpyrauxifen-benzyl in early and medium planting time was greater than at late planting time. Herbicide applications at V2 with 60 g ai ha-1 of florpyrauxifenbenzyl reached higher injury than at V6 or R0 through the evaluation period with no yield reduction. The average in doses that cause 50% of plant injury (ED50) and growth reduction (GR50) were >6-fold, >4-fold, and 2.7-fold times the label rate (30 g ai ha-1) when applied florpyrauxifen-benzyl alone, with malathion, and with dietholate followed by piperonyl butoxide, respectively. 'Pampeira' cultivar showed lower ED50 and GR50 than IRGA 424 RI. Rice plant injury was greater in treatments where temperature increase from 28/25ºC to 38/36ºC rather than those that decrease from 28/25ºC to 18/15ºC for the 24 hours after application. Temperature changes suggest downregulation of CYP71A21, OsGSTL3, and OsWALK21.2. Results from these experiments suggest florpyrauxifen-benzyl injuries to rice do not cause lasting negative effects. Spraying malathion before florpyrauxifen-benzyl does not reduce the selectivity; however, the addition of two P450 inhibitors (dietholate and piperonyl butoxide) decreases the doses that cause 50% of growth reduction, but it seems to not compromise the crop selectivity. Pampeira cultivar showed less tolerance to florpyrauxifen-benzyl but doses required to GR50 was 2.9 times? the label rate. High temperature before or after florpyrauxifen-benzyl spraying time can increase rice plant injury due, in part, to the reduction of plants herbicide detoxification.