Population genetics structure of glyphosate-resistant Johnsongrass (Sorghum halepense L. Pers) does not support a single origin of the resistance

FERNÁNDEZ L.; DE HARO L.; DISTEFANO A.J.; MARTINEZ M.C.; LIA V.V.; PAPA J.C.; OLEA I.; TOSTO D.; HOPP H.E.

Ecology and Evolution

Wiley

Año: 2013 vol. 3 p. 3388 - 3400

2045-7758

Single sequence repeats (SSR) developedfor 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 todifferent geographic regions do not share similar genetic backgrounds. In contrast, they show closer similarity to their neighboring susceptible counter- parts. Discriminant Analysis of Principal Components using the clusters identi fied 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 fromdifferent geographic origins showed that none presented expected mutations inaminoacid positions 101 and 106 which are diagnostic of target-site resistance mechanism.