Yellow nutsedge is one of the most problematic weedy sedges in ricesoybean 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 Resbiotype 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 Resyellow nutsedge biotype and purple nutsedge. Tuber production per plant and tuber weight of the Resbiotype were less than that of the Susbiotypes. Differences in quantitative traits, such as shoot and tuber production existed between the Resand Susbiotypes 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 Resbiotype at a 14-h photoperiod. Over a 90-d period, inflorescence formation was only observed in the Resbiotype 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 Resyellow nutsedge. Phylogenetic analysis based on ribosomal DNA internal transcribed spacer (ITS) regions and mitochondrial nad4gene intergenic spacer sequences indicated that the Resbiotype was more closely associated with Susyellow nutsedge biotypes. Nevertheless, 100% similarity for the nad4gene sequences between the Resyellow nutsedge biotype and a reference purple nutsedge suggests that the Resbiotype is likely a result of hybridization between yellow and purple nutsedges, which perhaps explains the intermediary growth characteristics observed in the Resbiotype.