Response of rice (Oryza sativa) genotypes to weed management in rainfed ecosystems of eastern India

An experiment was conducted during the rainy seasons of 2013 and 2014 at Patna, Bihar, to study perfor- mance of 9 rice (Oryza sativa L.) genotypes (Sahbhagi Dhan, Sushk Samrat, CR Dhan 40, Abhishek, IR 84899-B-183-CRA-19-1, IR 83387-B-B-40-1, IR 82870-11, IR 83387-B-B-27-4 and IR 83376-B-B-24-2) under 2 weed-management levels [pendimethalin 1.0 kg/ha followed by (fb) bispyribac-sodium 30 g/ha at 20 days after sowing (DAS) and 2 hand-weedings at 45 and 65 DASlow weed pressure; and pendimethalin 1.0 kg/ha alone medium weed pressure] in the rainfed ecosystem of eastern India. The field was infested mainly with barnyard grass [Echinochloa colona L. (Link)], horse purselane (Trianthema portulacastrum L.), native gooseberry (Physalis minia), purple nutsedge (Cyperus rotundus L.) and lesser fimbristylis [Fimbristylis miliacea L. (Vahl.)]. Significant genotypic differences in competitiveness against weeds were observed. Weed-competitive index was the highest (1.5) for IR 84899-B-183-CRA-19-1 and the lowest (0.43) for IR 83376-B-B-24-2. Grain-yield reduction among the cultivars due to weed competition varied from 6.6% in IR 82870-11 to 30.4% in Sahbhagi Dhan during 2013 and 6.5% in IR 82870-11 to 52.3% in Shusk Samrat during 2014. Across the weed pressure, rice genotype IR 84899-B-183-CRA-19-1 (2.75 and 2.28 t/ha) had higher grain yield during both the years. The advanced breeding line IR 84899-B-183-CRA-19-1 and the released variety CR Dhan 40 had superior weed-suppressing ability, while IR 83387-B-B-27-4 had the higher weed tolerance. Pre-emergence application of pendimethalin fb post- emergence application of bispyribac-sodium and hand-weeding significantly reduced the weed infestation and re- sulted in higher yield and profits in dry direct-seeded rainfed upland rice.