Ludovic Capo-Chichi1, Edzard van Santen2, and Paul Raymer1. (1) Univ of Georgia, Crop and Soil Science Department, 1109 Experiment St, Griffin, GA 30223-1797, (2) Auburn University, 202 Funchess Hall, Auburn, AL 36849
Molecular markers contribute to our understanding of the
entry, spread, and evolution of invasive species as a foundation upon which
appropriate management strategies are developed. Cogongrass (Imperata cylindrica L.
Beauv.), introduced into the United States shortly after the turn of the
twentieth century, is an aggressive, invasive weed species that colonizes a
diverse range of habitats. Genotypic diversity and spread dynamics at the
point of initial introduction and its adjacent areas in the southern United States were estimated. Clones evaluated from nine populations with
two primer combinations produced a total of 137 AFLP loci of which 102 (74.4%)
were polymorphic. Among population
variance accounted for 44% of the total variance. The species exhibits no genetic structure inferred
from 24 populations along putative routes of dispersal. Only 6.9% (P > 0.05) of the total
variance was partitioned between eastern and western areas of the State of Alabama. Within population variance component was estimated
to be 35.8 % (P < 0.05) of the total variation while among
populations gathered 57.2% (P
< 0.05), suggesting that asexual reproduction through rhizomes and sexual
reproduction by seed significantly impact the genetic structure of I. cylindrica
populations. Gene flow (Nm) values ranged from 0.6 to 5.7. The absence of significant relationship
between geographic and genetic distances suggests that the spread dynamics of I. cylindrica into the southern United States is primary through
human activities and to a lesser extent by natural dispersal mechanisms. High levels of genetic differentiation were
found between populations regardless of the geographic distance that separate
them. When assessed by Mantel's tests, there is no correlation between
gene flow and geographic distance.