Growth form variations of Amaranthus hybridus L. biotypes with EPSPS mutations

Several Amaranthus hybridus L. biotypes present single and triple amino acid substitutions in EPSPS (5-enolypyruvylshikimate-3-phosphate synthase). In resistant and tolerant species to glyphosate, differential susceptibility and alterations in the EPSPS sequence could cause modifications in their morphological-structural characteristics, an issue that is unknown for biotypes of A. hybridus. The aim of the work was to determine the susceptibility to glyphosate, the presence of mutations in EPSPS and the growth form in four biotypes of this weed from north-central Argentina. To carry out this, a dose-response assay was conducted, to determine the presence of mutations in the EPSPS, DNA was extracted, amplified and sequenced, and finally, to evaluate the morphological-structural variations, the growth form was analysed. Our findings revealed that Ah03, Ah07 and Ah36 biotypes had resistance factors of 22 to 118. The EPSPS sequence remains unaltered in the Ah39 biotype, leading it to be considered a susceptible biotype. Biotypes Ah03 and Ah36 had heterozygous changes in the DNA sequence resulting in amino acid substitutions at positions 102, 103 and 106 being considered resistant biotypes, whereas in Ah07 some individuals showed unaltered DNA sequences and others exhibited heterozygous changes. The growth form was quantitatively different between biotypes, standing the most susceptible biotype that produced more seeds and required less thermal time for the appearance of the terminal inflorescence. The present investigation provides new evidence that resistant biotypes with the triple DNA mutation exhibit variations in the growth form compared to susceptible biotypes of this weed.