Acetolactate Synthase–Inhibitor Resistance in Yellow Nutsedge (Cyperus esculentus): II—Physiognomy and Photoperiodic Response

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.