Susceptibility to imazamox in Italian weedy rice populations and Clearfield^® rice varieties

Abstract

Summary The introduction of imidazolinone‐tolerant rice varieties has made selective Oryza sativa (weedy rice) control possible. We hypothesised that Italian weedy rice populations have variable degrees of susceptibility to imazamox prior to imidazolinone‐tolerant variety introduction. To this end, 149 Italian weedy rice populations collected from fields never before cultivated with imidazolinone‐tolerant varieties were tested in a glasshouse‐based, whole‐plant response screening study. Imazamox was applied to all populations post‐emergence at a rate of 70 g a.i. ha−1, resulting in 70–90% shoot biomass reduction in the majority of cases. The results prompted a second study of the seedling dose response of four weedy rice populations from the initial study group. Three imidazolinone‐tolerant and one conventional rice variety were also included. The seedling roots were cut six days after germination and exposed to different concentrations of imazamox. The root regrowth associated with each concentration‐exposure was then measured. Imazamox concentrations to inhibit weedy rice root growth by 50% varied by about two orders of magnitude, or between 0.0018 and 0.12 mm. Even with this result, imidazolinone‐tolerant varieties were at least 31.8 times less susceptible than weedy rice populations, suggesting that Italian weedy rice populations were not tolerant to imazamox before introduction of these varieties.

Evolutionary and social consequences of introgression of nontransgenic herbicide resistance from rice to weedy rice in Brazil

“…However, several biotypes of weedy rice resistant to ALS-inhibiting herbicides were identified in rice paddy fields three growing seasons after the introduction of IMI-rice to Brazil (Menezes et al 2009;Roso et al 2010b). Similar problems were found in the United States (Shivrain et al 2007), Italy (Andres et al 2014) and Greece (Kaloumenos et al 2013). This problem is challenging the use of IMI-rice because heavy infestations of weedy rice are still present in several fields similarly to the situation that occurred before the introduction of IMI-rice technology.…”

“…; Andres et al. ) should be considered to avoid or minimize the problems associated with this technology. The ALS gene mutations Ala122Thr and Ser653Asn that confer high level of resistance should be used for developing local IMI‐rice cultivars.…”

“…Different from the United States where IMIrice is also cultivated in a large area and where a single ALS mutation is used as the predominant source of resistance, in Brazil, three different ALS mutations were used to develop the IMI-rice varieties (Roso et al 2010b). Therefore, the different consequences of these mutations at molecular level and the implications regarding herbicide use and crop management in this region resulted in several particularities in the evolution of herbicide resistance in weedy rice in comparison with similar processes that occurred elsewhere (Kaloumenos et al 2013;Andres et al 2014;Burgos et al 2014).…”

“…IMI-rice cultivars are starting to be used in several rice growing regions of Asia and South and Central America. The consequences related to the gene flow to weedy rice that occurred in the major areas where IMI-rice has been used in southern Brazil, as described in this review, and in the United States (Gealy et al 2003;Sudianto et al 2013;Burgos et al 2014) and Europe (Kaloumenos et al 2013;Andres et al 2014) should be considered to avoid or minimize the problems associated with this technology. The ALS gene mutations Ala122Thr and Ser653Asn that confer high level of resistance should be used for developing local IMI-rice cultivars.…”

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

“…Results from seed bioassay indicate that the continuous exposure of the pre-germinated seeds to the IMI-herbicides has had a significant impact on the seeds growth. The variability of sensitivity to IMI-herbicides among weedy rice populations in petri dish seed bioassay have also been observed in the USA [3,24], Greece [17,25], and Italy [26]. Zhou et al [27] suggested that AHAS inhibition can be achieved at a very low herbicide concentration, similar with the data obtained for those sensitive populations in this experiment (C, S, and MR219), where up to 99% of inhibition was recorded at only 0.25 times recommended concentration.…”