Acetolactate Synthase–Inhibitor Resistance in Yellow Nutsedge (Cyperus esculentus): II—Physiognomy and Photoperiodic Response Parsa Tehranchian, Jason K. Norsworthy, Muthukumar V. Bagavathiannan, and Dilpreet S. Riar* Yellow nutsedge is one of the most problematic weedy sedges in rice–soybean systems of the Mississippi Delta region. An acetolactate synthase (ALS)-inhibiting, herbicide-resistant (Res) yellow nutsedge biotype was recently documented in eastern Arkansas, which showed intermediary growth habit between yellow nutsedge and purple nutsedge and also exhibited differential photoperiodic sensitivity to flowering. The objectives of this study were to: (a) determine variation in reproductive characteristics of the Res biotype and three susceptible (Sus) yellow nutsedge biotypes, (b) understand the influence of photoperiod on growth and reproduction, (c) understand the potential role of seeds in population establishment, and (d) elucidate the phylogenetic relationships between the Res yellow nutsedge biotype and purple nutsedge. Tuber production per plant and tuber weight of the Res biotype were less than that of the Sus biotypes. Differences in quantitative traits, such as shoot and tuber production existed between the Res and Sus biotypes for photoperiods ranging from 12 to 16 h. Generally, photoperiods greater than 12 h increased shoot development in all yellow nutsedge biotypes, with differential responses among the biotypes. Number of tubers reached the maximum for the Res biotype at a 14-h photoperiod. Over a 90-d period, inflorescence formation was only observed in the Res biotype with maximum flowering and seed production in the 14-h photoperiod. Subsequent tests revealed up to 18% seed germination, suggesting that seed could also play a role (in addition to tubers) in the persistence and spread of the Res yellow nutsedge. Phylogenetic analysis based on ribosomal DNA internal transcribed spacer (ITS) regions and mitochondrial nad4 gene intergenic spacer sequences indicated that the Res biotype was more closely associated with Sus yellow nutsedge biotypes. Nevertheless, 100% similarity for the nad4 gene sequences between the Res yellow nutsedge biotype and a reference purple nutsedge suggests that the Res biotype is likely a result of hybridization between yellow and purple nutsedges, which perhaps explains the intermediary growth characteristics observed in the Res biotype. Nomenclature: Purple nutsedge, Cyperus rotundus L.; yellow nutsedge, Cyperus esculentus L.; rice, Oryza sativa L.; soybean, Glycine max (L.) Merr. Key words: ALS-inhibiting herbicide-resistant perennial weed, hybridization, internal transcribed spacer (ITS), mitochondrial nad4 gene, photoperiodic response, phylogeny, quantitative traits. Yellow nutsedge is one of the most important perennial herbaceous members of the Cyperaceae family with a C 4 photosynthetic pathway (DeFelice 2002). It is a tuber-forming sedge endemic in Eurasia and reported to be naturalized within the United States by 1850s (Bartlett 1889). Yellow nutsedge is an invasive and a persistent weed in well-irrigated agricultural and horticultural crops (Ransom et al. 2009; Webster 2005), and a noxious weed in Arkansas rice–soybean rotations (Nors- worthy et al. 2013). Chemical control, particularly with acetolactate synthase (ALS)-inhibiting herbi- cides, in comparison to cultural and mechanical control, has been the most effective means for managing this weed species. Recently, a nutsedge biotype identified as yellow nutsedge by a USDA plant taxonomist (Dr. Charles Bryson) exhibited resistance to several ALS-inhibiting herbicides com- monly used in Arkansas rice production (Tehran- chian et al. 2014b). Yellow nutsedge propagates asexually by forming underground tubers at the apical end of creeping fibrous rhizomes (Mulligan and Junkins 1976). It invades farmlands with extensive root and rhizome proliferation and massive tuber production (DeFelice 2002). A three-dimensional spatial model developed by Schippers et al. (1993) suggested that tillage and field machinery are the main causes of yellow nutsedge dispersal in agricultural fields. Tubers usually sprout in late spring, developing a basal bulb and then an aerial shoot. Under suitable conditions, DOI: 10.1614/WS-D-14-00187.1 * First and second authors: Postdoctoral Research Associate and Professor, Department of Crop, Soil, and Environmental Sciences, University of Arkansas, 1366 West Altheimer Drive, Fayetteville, AR 72704; third author: Assistant Professor, Department of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843; fourth author: Associate Scientist, Dow AgroSciences, Indianapolis, IN, 46268. Corresponding author’s E-mail: ptehranc@uark.edu Weed Science 2015 63:819–827 Tehranchian et al.: ALS–inhibitor-resistant yellow nutsedge N 819 https://doi.org/10.1614/WS-D-14-00187.1 Downloaded from https://www.cambridge.org/core. IP address: 34.228.24.229, on 12 Jun 2020 at 16:42:11, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.