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Inconsistent control of Echinochloa oryzoides has been reported repeatedly by farmers in the major rice growing area of Turkey. Greenhouse studies confirmed the existence of cross and multiple herbicide tolerance of E. oryzoides accessions including acetolactate synthase (penoxsulam, bispyribac-sodium) and acetyl CoA carboxylase (cyhalofob-butyl) inhibiting herbicides. Comparison of 95% lower confidence intervals of ED 90 derived from log-logistic dose–response curves, and twice the recommended field rates of the herbicides showed some, but not distinct separation of susceptible and tolerant accessions. We used a novel method to separate heterogeneous data without a priori knowledge of grouping into more than one group. On the basis of the distribution of ED 90 it was possible to identify two distinct groups of the 172 accessions tested, 78% were not controlled by ALS inhibitors (penoxsulam, and bispyribac-sodium) at recommended field rates; and 38% were not controlled by the ACCase Inhibitor (cyhalofob-butyl) at twice the field rates. The effective response level of ED 90 resulted in 64 and 14 tolerant accessions to ALS and ACCase, respectively. Fourteen accessions showed multiple resistances to ALS and ACCase Inhibitors. Some of the accessions were strongly tolerant to both herbicide modes of action and had 100% survival even at 6 times the recommended rates. Most of these tolerant accessions were from Marmara region, predominantly in Edirne and Balıkesir, which are the regions without any crop rotation. [ABSTRACT FROM AUTHOR]

Abstract: Developing more competitive rice cultivars could help improve weed management and reduce dependency on herbicides. To achieve this goal, an understanding of key traits related to competitiveness is critical. Experiments were conducted at Gelemen and Bafra districts of Samsun province in Turkey between 2008 and 2009 to measure the competitiveness of rice cultivars against Echinochloa crus-galli, a problematic weed in rice fields. Five rice cultivars (Osmancık, Kızılırmak, Karadeniz, Koral and Neğiş) and five E. crus-galli densities (0, 5, 10, 20, and 30 plants m−2) were used. Koral produced significantly more tillers than the other cultivars irrespective of E. crus-galli densities and reduced E. crus-galli tiller production by about 29.5% at Gelemen and 15.8% at Bafra at the highest weed density. E. crus-galli interference reduced rice height and there was a density dependent relationship. Koral was the most competitive cultivar; it maintained high biomass accumulation in early growth stages and suffered smaller reductions in plant height in the presence of E. crus-galli, compared to the other cultivars. In the absence of weed competition, Koral and Neğiş produced the highest yields at both locations. Stepwise regression analyses of the combined data from both years showed tillering capacity, early growth crop biomass, and plant height were critical traits related to competitiveness. These traits should be considered by plant breeders in their efforts to develop rice cultivars with enhanced competitiveness against weeds. Development of such cultivars could substantially reduce herbicide and labor inputs for rice production. [Copyright &y& Elsevier]