NOVAK, STEPHEN J.1,2*, JOHN K. SCOTT2, and PAUL C. QUIMBY3. 1Department of Biology, Boise State University, Boise, ID 83725, USA; 2CSIRO European Laboratory, Campus International de Baillarguet, Montferrier-sur-Lez, France; 3USDA European Biological Control Laboratory, Campus International de Baillarguet, Montferrier-sur-Lez, France. - Genetic diversity is low in naturalized populations of Lepidium latifolium (Brassicaceae) from southern France.
Lepidium latifolium L. is a polyploid, perennial herbaceous
plant with semi-woody stems, and creeping rhizomes, that is native or
naturalized throughout much of Eurasia. This species was accidentally
introduced into the USA, and has become a noxious weed in coastal New
England and wetlands, meadows, pastures, and riparian areas of many
western States, especially California and Nevada. The work reported
here represents our initial attempt to determine the genetic diversity
of L. latifolium in Eurasia. We assessed genetic diversity in
six populations (380 individuals) of this species from the
Mediterranean coast of southern France by staining for 14 enzymes that
were coded for by 29 loci. Genetic diversity in L. latifolium
is extremely low: we detected only two multilocus genotypes across all
six populations. Five populations (280 individuals) were fixed for a
single multilocus genotype, whereas all 100 individuals in the sixth
(and easternmost) population were fixed for the other genotype. Enzyme
banding patterns are consistent with allopolyploid gene expression,
and chromosome counts reveal that all populations possess tetraploid
chromosome numbers (2n = 24). The low levels of genetic diversity we
report for L. latifolium may result from two factors: 1) these
populations may have experienced a genetic bottleneck associated with
their relatively recent naturalization in this region of southern
France, and 2) these populations appear to reproduce almost
exclusively through clonal means by rhizome expansion and
fragmentation. Our results clearly indicate that further sampling and
analysis of L. latifolium across larger portions of Eurasia is
required before a better picture of genetic diversity in this species
in its native range can be obtained.
Key words: Brassicaceae, clonal reproduction, genetic diversity, Lepidium latifolium, multilocus genotypes, naturalized populations