Abstract:
Increased infestation of weedy rice—a noxious agricultural pest has caused
significant reduction of grain yield of cultivated rice (Oryza sativa) worldwide.
Knowledge on genetic diversity and structure of weedy rice populations will
facilitate the design of effective methods to control this weed by tracing its origins
and dispersal patterns in a given region. To generate such knowledge, we studied
genetic diversity and structure of 21 weedy rice populations from Sri Lanka based
on 23 selected microsatellite (SSR) loci. Results indicated an exceptionally high
level of within-population genetic diversity (He50.62) and limited among-population
differentiation (Fst50.17) for this predominantly self-pollinating weed. UPGMA
analysis showed a loose genetic affinity of the weedy rice populations in relation to
their geographical locations, and no obvious genetic structure among populations
across the country. This phenomenon was associated with the considerable
amount of gene flow between populations. Limited admixture from STRUCTURE
analyses suggested a very low level of hybridization (pollen-mediated gene flow)
between populations. The abundant within-population genetic diversity coupled
with limited population genetic structure and differentiation is likely caused by the
considerable seed-mediated gene flow of weedy rice along with the long-distance
exchange of farmer-saved rice seeds between weedy-rice contaminated regions in
Sri Lanka. In addition to other effective weed management strategies, promoting
the application of certified rice seeds with no weedy rice contamination should be
the immediate action to significantly reduce the proliferation and infestation of this
weed in rice ecosystems in countries with similar rice farming styles as in Sri Lanka.
