Cross-Resistance to Imazapic and Imazapyr in a Weedy Rice (Oryza sativa) Biotype Found in Malaysia

Abstract

Planta Daninha 2018; v36:e018182239 DILIPKUMAR, M. et al. Cross-resistance to imazapic and imazapyr in a weedy rice (Oryza sativa) biotype found in Malaysia 1 151103-PD-2016 (9 páginas) PROVA GRÁFICA ABSTRACT -The Clearfield ® rice production system is an effective management tool for weedy rice and other weeds in the direct-seeded rice culture. However, if farmers cultivating the Clearfield ® rice disregard stewardship recommendations, the industry could face a problem of herbicide-resistant weedy rice which would occur through the selection of outcrosses. This study aimed to confirm imidazolinoneresistant weedy rice in Malaysia. The resistant weedy rice (R-WR) was found to be 67 fold more resistant to OnDuty ® (premix of imazapic and imazapyr) than the susceptible weedy rice (S-WR) based on the GR 50 values (rate that causes 50% inhibition of shoot growth). The Clearfield ® rice cultivar was 32-fold more tolerant to OnDuty ® than the S-WR. Furthermore, the R-WR was 54 and 89 fold more resistant to imazapic and imazapyr applied separately than the S-WR, respectively. The Clearfield ® rice was 140-and 40-fold more tolerant to imazapic and imazapyr, respectively than the S-WR. The R-WR biotype was susceptible to non-selective herbicides glyphosate and glufosinate, as well as the selective graminicide quizalofop. Oxadiazon controlled the R-WR biotype, but pretilachlor was ineffective. The present study documented the first case of weedy rice that was cross-resistant to imazapic and imazapyr in Malaysian Clearfield ® rice field. Keywords:Clearfield ® system, imidazolinone-resistance, direct-seeded rice, ALS-inhibitor herbicide, ACCase-inhibitor herbicide. RESUMO -O sistema de produção de arroz

Ser-653-Asn substitution in the acetohydroxyacid synthase gene confers resistance in weedy rice to imidazolinone herbicides in Malaysia

“…The MR220CL2 variety presented the highest LD 50 value and moderate resistance to IMI herbicides at the whole-plant level ( Table 2 ). MR220CL2 exhibited greater resistance to IMI herbicides in the seed bioassay than in the whole-plant dose-response, which is in agreement with the findings of Dilipkumar et al [ 16 ]. Interestingly, even though this herbicide-resistant rice variety exhibited higher resistance to IMI herbicides than the weedy rice populations, a significant reduction in survival rate and shoot dry weight was recorded with herbicide application at 2 times the recommended rate (308 g a.i.…”

“…Recently, rice growers who have been cultivating IMI-rice for more than eight planting seasons in Selangor, Perak, Pulau Pinang, Kedah, and Perlis states of Malaysia have reported reduced efficacy of IMI herbicides to control weedy rice and other weed species in their fields. More recent findings have confirmed the evolution of IMI resistance in weedy rice populations of Pendang, Kedah, with weedy rice exhibiting 67-fold greater resistance than the susceptible population [ 16 ]. Presently, there is a high risk of the evolution of IMI resistance in Malaysian weedy rice populations.…”

“…In the Malaysian IMI-rice Clearfield Stewardship, it is clearly stated that IMI herbicides must be applied pre- or early post-emergence, particularly between 0 and 5 days after sowing (when rice and weedy rice seedlings are at the 1–2-leaf stage), for effective weedy rice control. Hence, early application of IMI herbicides is crucial, and late application (12 days after sowing) can reduce its efficacy and expedite resistance evolution in weedy rice [ 16 ].…”

“…The use of herbicide-resistant rice cultivars, such as IMI-rice varieties, were advocated by researchers and government in 2010, has been a successful strategy for the selective control of weedy rice in cultivated rice fields. However, over-reliance on the same weedy rice management method by rice growers has resulted in the evolution of herbicide resistance in weedy rice [ 15 , 16 , 20 ]. Another concern is on the occurrence of hybridization between IMI-rice and weedy rice, and the potential crosses among the weedy rice variants [ 21 – 25 ], as they may affect the future of herbicide-resistant rice technology.…”

Ser-653-Asn substitution in the acetohydroxyacid synthase gene confers resistance in weedy rice to imidazolinone herbicides imazapic and imazapyr in Malaysia

“…Recently, rice-growers who have been practicing IMI-herbicides rice package for more than eight planting seasons in Selangor, Perak, Pulau Pinang, Kedah, and Perlis of Malaysia have been complaining about the reduced efficacy of IMI-herbicides to control weedy rice and other weed species in their fields. In more recent findings, it was reported that weedy rice population collected from Pendang, Kedah have been confirmed to have developed resistance to the IMI-herbicides with the resistance level up to 67-fold greater than the susceptible population [15]. The risk of resistance evolution in weedy rice to the IMI-herbicides in Malaysia is now highly alarmed.…”