Resistance in smallflower umbrella sedge (Cyperus difformis) to an acetolactate synthase–inhibiting herbicide in rice: first case in India

Abstract

Smallflower umbrella sedge is one of the problematic weeds in direct-seeded rice in India. Bispyribac-sodium (acetolactate synthase-inhibiting herbicide) is a commonly used in rice, but recently growers have reported lack of smallflower umbrella sedge control with this herbicide. An extensive survey was carried out in two rice growing states, Chhattisgarh and Kerala, where 53 putative bispyribac-sodium resistant (BR) biotypes were collected. Studies were conducted to confirm resistance to bispyribac-sodium and to test the efficacy of newly developed synthetic auxin herbicide florpyrauxifen-benzyl on putative BR biotypes. Whole-plant bioassay revealed that bispyribac-sodium is no longer effective. Of 53 putative BR biotypes, 17 biotypes survived recommended label rate of 25 g ai ha−1. Effective bispyribac-sodium rate required to control 50% of the plants in most of the BR biotypes (ED50) ranged from 19 to 96 g ha−1 whereas it was 10 g ha−1 in susceptible biotype. In two highly resistant biotypes, ED50 was beyond the maximum tested rate, 200 g ha−1. This suggests 2 to >20-fold resistance in BR biotypes. Acetolactate synthase (ALS) enzyme activity assay suggests altered target site as mechanism of resistance to bispyribac-sodium. This study confirms the first case of evolved resistance in smallflower umbrella sedge for bispyribac-sodium in India. However, the newly developed synthetic auxin, florpyrauxifen-benzyl effectively controlled all BR biotypes at the field use rate 31.25 g ae ha−1.

Challenges and technological interventions in rice–wheat system for resilient food–water–energy-environment nexus in North-western Indo-Gangetic Plains: A review

“…The sole reliance on these practices have resulted in the rapid evolution of imidazolinone-resistant weedy rice, problem of gene flow and accelerated development of resistance in other weed species (Kumar et al 2008;Avila et al 2021). Further, matter of concern is that first case of herbicide resistance in Cyperus difformis L. against bispyribac-sodium (ALS inhibitor) in India (Choudhary et al 2021) was reported recently having the similar mode of action. Nevertheless, comprehensive studies are needed regarding the comparative saving of irrigation water in direct seeded rice keeping in view the farmers' practice of early seeding during the peak evapotranspirative demand in summers and consequent frequent irrigations.…”

“…The continuous cultivation of rice-wheat system along with faulty spray techniques have resulted in accelerated herbicide resistance in wheat associated weeds such as Phalaris minor and Rumex dentatus (Chhokar et al 2018). Recently in rice also, first case of herbicide resistance in Cyperus difformis L. against bispyribac-sodium was reported in India (Choudhary et al 2021). The effective dose of bispyribac-sodium required to control 50% of plants was found 19-96 g ha −1 as compared to 10 g ha −1 for susceptible.…”

First report on ALS herbicide resistance in barnyardgrass (Echinochloa crus-galli) from rice fields of India

“…However, ALS-resistant barnyardgrass has not yet been confirmed in India. Recently, bispyribac-sodium resistance in another predominant weed, smallflower umbrella sedge ( Cyperus difformis ), has been reported in rice fields in India (Choudhary et al 2021). Hence it is possible that barnyardgrass has developed resistance to the herbicide.…”