Abstract
BackgroundIntrogression plays an important role in evolution of plant species via its influences on genetic diversity and differentiation. Outcrossing determines the level of introgression but little is known about the relationships of outcrossing rates, genetic diversity, and differentiation particularly in a weedy taxon that coexists with its conspecific crop.Methodology/Principal FindingsEleven weedy rice (Oryza sativa f. spontanea) populations from China were analyzed using microsatellite (SSR) fingerprints to study outcrossing rate and its relationship with genetic variability and differentiation. To estimate outcrossing, six highly polymorphic SSR loci were used to analyze >5500 progeny from 216 weedy rice families, applying a mixed mating model; to estimate genetic diversity and differentiation, 22 SSR loci were analyzed based on 301 weedy individuals. Additionally, four weed-crop shared SSR loci were used to estimate the influence of introgression from rice cultivars on weedy rice differentiation. Outcrossing rates varied significantly (0.4∼11.7%) among weedy rice populations showing relatively high overall Nei's genetic diversity (0.635). The observed heterozygosity was significantly correlated with outcrossing rates among populations (r2 = 0.783; P<0.001) although no obvious correlation between outcrossing rates and genetic diversity parameters was observed. Allelic introgression from rice cultivars to their coexisting weedy rice was detected. Weedy rice populations demonstrated considerable genetic differentiation that was correlated with their spatial distribution (r2 = 0.734; P<0.001), and possibly also influenced by the introgression from rice cultivars.Conclusions/SignificanceOutcrossing rates can significantly affect heterozygosity of populations, which may shape the evolutionary potential of weedy rice. Introgression from the conspecific crop rice can influence the genetic differentiation and possibly evolution of its coexisting weedy rice populations.
Highlights
Introgression, as defined in its broad sense ‘‘the transfer of genes between genetically distinguishable populations’’ [1], plays an important role in the evolution of plant species [2,3]
Average outcrossing rates of the 11 weedy rice populations were 4.1% as estimated by multilocus outcrossing rate, and 2.9% by single-locus outcrossing rate, indicating in general very low frequency of outcrossing in weedy rice populations, which correspond to the self-pollinating nature of weedy rice
A low level of biparental inbreeding that indicated outcrossing among closely related individuals was detected in all weedy rice populations (Table 3)
Summary
Introgression, as defined in its broad sense ‘‘the transfer of genes between genetically distinguishable populations’’ [1], plays an important role in the evolution of plant species [2,3]. It is important to understand the extent of crop-wild/weed gene flow and introgression that may cause potential evolutionary consequences. The extent of introgression between species (or populations) relies essentially on their outcrossing ability, which is usually determined by the genetic nature of a plant species [12,13,14]. Estimating outcrossing rates of pollen-recipients will facilitate our understanding on the potential hybridization and introgression of a plant species or population. Introgression plays an important role in evolution of plant species via its influences on genetic diversity and differentiation. Outcrossing determines the level of introgression but little is known about the relationships of outcrossing rates, genetic diversity, and differentiation in a weedy taxon that coexists with its conspecific crop
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