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 (He = 0.62) and limited among-population differentiation (Fst = 0.17) 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.
Highlights
Weeds continue to pose great challenges for crop productivity around the world, despite of decades of intensive efforts and practices for weed control and eradication [1, 2]
The primary objective of this study is to address the following questions: (1) Does abundant within-population genetic diversity exist in Sri Lankan weedy rice? (2) Is there any spatial genetic structure or differentiation among weedy rice populations across the country? (3) Does long-distance gene flow occur among weedy rice populations, which is associated with genetic diversity of Sri Lankan weedy rice? The answer of these questions will provide a useful guideline for designing effective strategies to control and manage weedy rice in Sri Lanka and in other countries that have similar or the same rice farming styles and seed management as in Sri Lanka
The 21 weedy rice populations collected from Sri Lanka showed a considerably high level of overall genetic diversity (He50.62) and within-population genetic diversity (He50.37-0.69), great diversity was detected among different populations (Table 3)
Summary
Weeds continue to pose great challenges for crop productivity around the world, despite of decades of intensive efforts and practices for weed control and eradication [1, 2]. Designing relevant strategies is necessary for the effective control and management of different types of weeds in agro-ecosystems This is true for weeds that are conspecific to crops, meaning that weeds and crops are the same biological species. The control and management of conspecific weeds become extremely complicated and difficult because these weeds can acquire genetic variation from crops through natural hybridization and introgression, through which genes from a crop variety can be transferred to a weedy population [4]. Such a process can facilitate the accumulation of genetic diversity and adaptive evolution of conspecific weeds in human disturbed agro-ecosystems. It is important to reveal the underlying mechanisms that influence the spread and accumulation of such genetic diversity, either through pollination or seed dispersal, in a given geographical region
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