Published online by Cambridge University Press: 20 January 2017
Acetolactate synthase (ALS) –inhibitor resistance has been recentlydocumented in a yellow nutsedge biotype in Arkansas rice production, with atarget-site mutation resulting in an amino acid substitution from Trp574 toLeu. Preliminary observations have indicated that the resistant biotypeshowed distinct phenotypic characteristics. Two greenhouse experiments wereconducted on the resistant biotype in comparison with three susceptiblestandards (1) to understand differential growth habit and spatialdistribution, and (2) to characterize shoot emergence pattern and seedlingvigor. The resistant biotype exhibited a drastically different growth habitwith secondary and tertiary basal bulbs emerging away from the parent shoot,resulting in a wider spatial distribution and ground coverage compared tothe very compact growth habit of susceptible biotypes. Unlike thesusceptible biotypes, the rhizomes developing into tubers were not oftenconnected to the primary basal bulb, but were originating randomly fromdaughter shoots. The resistant biotype produced an extensive subterraneannetwork of rhizomes and basal bulbs, with wider root spread and distributioncompared to the susceptible biotypes. The growth habit of the resistantbiotype appeared to be intermediate between yellow and purple nutsedges.Further, the resistant biotype showed a considerably delayed emergencepattern with relatively high levels of tuber dormancy. Although theresistant plants exhibited low early-growth seedling vigor and biomassproduction compared to the susceptible biotypes (perhaps because of smallertubers), final aboveground biomass production was greater than that ofsusceptible biotypes. The overall growth habit and phenotype of theresistant biotype may provide a competitive advantage over adjacent speciesthrough the ability to occupy niches and gain improved access to criticalresources. The distinct growth pattern may also mean that tillage should notbe relied upon for control because it can assist further spread bydisconnecting and displacing the chains of rhizomes.
Associate Editor for this paper: Theodore M. Webster, USDA-ARS.