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ARS Home » Southeast Area » Tifton, Georgia » Crop Protection and Management Research » Research » Publications at this Location » Publication #233762
Title: Pollen Grain Size, Density, and Settling Velocity for Palmer Amaranth (Amaranthus palmeri)

Author
item SOSNOSKIE, L - UNIV OF GA
item Webster, Theodore
item DALES, D - UNIV OF GA
item RAINS, G - UNIV OF GA
item GREY, T - UNIV OF GA
item CULPEPPER, A - UNIV OF GA

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2009
Publication Date: 7/1/2009
Citation: Sosnoskie, L.M., Webster, T.M., Dales, D., Rains, G.C., Grey, T.L., Culpepper, A.S. 2009. Pollen grain size, density, and settling velocity for Palmer Amaranth (Amaranthus palmeri). Weed Science. 57:404-409.

Interpretive Summary: Palmer amaranth, an annual plant native to the southwestern US, has invaded the mid-south and southeastern US, where it is a significant weed of agricultural environments. In Georgia, Palmer amaranth populations have developed resistance to two classes of herbicides, acetolactate synthase (ALS)-inhibiting herbicides and glyphosate. As of 2007, five states (Arkansas, Kansas, North Carolina, South Carolina and Tennessee), in addition to Georgia, have confirmed cases of ALS-resistant Palmer amaranth and five states (Arkansas, Georgia, North Carolina, South Carolina, and Tennessee) have biotypes resistant to glyphosate. A better understanding of pollen-flow dynamics and the mechanisms by which herbicide resistance traits can be exchanged between populations will allow us to monitor suspect populations, refine our scouting strategies, and install preventative treatments in areas in proximity to identified herbicide-resistant populations. This area of research will likely become more important in the development of weed management systems as more wind-dispersed species evolve herbicide resistance or other ecologically significant traits that can be transferred through pollen and improve fitness, both within and outside of managed agroecosystems.

Technical Abstract: Palmer amaranth has known resistance to several herbicides, including glyphosate, and there is concern that the resistance traits are being transferred between spatially segregated populations via pollen movement. The objective of this study was to describe the physical properties of Palmer amaranth pollen, specifically size, density, and settling velocity (Vs), that influence pollen flight. Data indicated that the mean diameter for Palmer amaranth pollen, as determined by light microscopy, was 31 µm (range of 21 to 38 µm); mean pollen diameter as measured using an electronic particle sizer was 27 µm (range of 21 to 35 µm). The mean density of the solid portion of the pollen grain was 1,435 kg m-3. Accounting for the density of the aqueous fraction, the mean density of a fully-hydrated pollen grain was 1,218 kg m-3. Using Stokes' law, the estimated mean theoretical Vs for individual Palmer amaranth pollen grains was 2.6 cm s-1 for a range of pollen diameters with a mean of 27 µm, and 3.4 cm s-1 for a range of pollen diameters with a mean of 31 µm. Results from the laboratory studies indicated that the majority of single pollen grains, settled at a rate of 4.9 cm s-1. The difference between the theoretical and empirical estimates of Vs was likely due to changes in pollen density and shape post-anthesis, which are not accounted for using Stokes’ law, as well as the presence pollen clusters.