Abstract
Single sequence repeats (SSR) developed for Sorghum bicolor were used to characterize the genetic distance of 46 different Sorghum halepense (Johnsongrass) accessions from Argentina some of which have evolved toward glyphosate resistance. Since Johnsongrass is an allotetraploid and only one subgenome is homologous to cultivated sorghum, some SSR loci amplified up to two alleles while others (presumably more conserved loci) amplified up to four alleles. Twelve SSR providing information of 24 loci representative of Johnsongrass genome were selected for genetic distance characterization. All of them were highly polymorphic, which was evidenced by the number of different alleles found in the samples studied, in some of them up to 20. UPGMA and Mantel analysis showed that Johnsongrass glyphosate-resistant accessions that belong to different geographic regions do not share similar genetic backgrounds. In contrast, they show closer similarity to their neighboring susceptible counterparts. Discriminant Analysis of Principal Components using the clusters identified by K-means support the lack of a clear pattern of association among samples and resistance status or province of origin. Consequently, these results do not support a single genetic origin of glyphosate resistance. Nucleotide sequencing of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) encoding gene from glyphosate-resistant and susceptible accessions collected from different geographic origins showed that none presented expected mutations in aminoacid positions 101 and 106 which are diagnostic of target-site resistance mechanism.
Highlights
Ecology and Evolution published by John Wiley & Sons Ltd
S. bicolor, as many as 7000 putative Single sequence repeats (SSR) markers were reported and contributed to the construction of many different saturated genetic maps, like the ones recently reported by Li et al (2009), Mace et al (2009), or Ramu et al (2010), some of which were readily adapted to Johnsongrass (Chang et al 2007; Wu and Huang 2006; Guo et al 2008; Hopp et al 2010; Jessup et al 2012)
This is because S. halepense is an allotetraploid containing one subgenome which is homologous to S. bicolor and another subgenome that originated from S. propinquum
Summary
These same molecular markers have been used to study the potential risk associated with the use of genetically modified sorghum through gene escape after hybridization between S. bicolor and S. halepense (Morrell et al 2005). None of these studies have carried out a population genetics analysis of Johnsongrass in relationship with herbicide-resistance propagation and epidemiology using molecular markers.
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