Monitoring and Management of Imidazolinone-Resistant Red Rice (Oryza sativa L., var. sylvatica) in Clearfield® Italian Paddy Rice

The introduction in Italy of Clearfield((R)) rice cultivars carrying imidazolinone-resistant traits provides an efficient option to control red rice, a conspecific weed of cultivated rice. However, despite the promulgation of specific guidelines for Clearfield((R)) technology management, imazamox red rice survivors have been reported by farmers. Forty-two fields were monitored in 2010 and 2011 throughout the Piedmont and Lombardy regions and field cases were recorded of herbicides use and agronomic practices. Whole-plant sensitivity to imazamox was assessed and the resistance mechanism was determined by molecular analysis. Twenty-six red rice populations out of 42 were imazamox-resistant and plants of all the resistant populations possess a Ser to Asn substitution at locus 653 of the ALS gene determining the target-site resistance. Farmers frequently grow Clearfield((R)) varieties for more than two consecutive years so increasing the selection pressure exerted by imazamox and favoring the evolution of resistant red rice. To maintain the sustainability of this new technology, a proper management based on crop rotation, utilization of certified seeds and strict control of red rice escapes has to be implemented. More generally, all stakeholders must increase their awareness that the selection pressure exerted by ALS inhibitors in rice cropping system should be reduced.