Molecular basis for resistance to tribenuron in shepherd’s purse (Capsella bursa-pastoris (L.) Medik.)

Capsella bursa-pastoris, a winter annual weed in the mustard family, can not be controlled by tribenuron after the herbicide has been continuously used for several years. The resistant biotype Lz-R was the generation of a population collected from Liangzhu, a place where tribenuron had been used for more than 15 consecutive years. To confirm and characterize the resistance of C. bursa-pastoris to tribenuron, whole-plant bioassays were conducted in the greenhouse. The results of whole-plant bioassays revealed that Lz-R was highly resistant to tribenuron with the resistance index (GR50 Lz-R)/(GR50 Lz-S) up to 236.6. To investigate the molecular basis of resistance in C. bursa-pastoris, the acetolactate synthase (ALS) genes were sequenced and compared between susceptible and resistant biotypes. Analysis of the nucleotide and deduced amino acid sequences between the biotypes indicated that one substitution had occurred in Domain A, cytosine by thymine (CCT to TCT) at position 197, that led to a change of the amino acid proline in the susceptible to serine in the Lz-R.

Domain A of ALS gene in both Capsella bursa-pastoris biotypes. Alignment of the nucleotide sequence of Domain A of the Lz-S and the Lz-R biotypes. Bold print in the amino acid sequence indicates the site confer resistance to ALS inhibitors, where CCT codon (Pro) in Lz-S biotype was substituted by a TCT codon (Ser) in Lz-R biotype.Figure optionsDownload as PowerPoint slideHighlights
► Lz- R was highly resistant to tribenuron with the resistance index up to 236.6.
► Pro in Lz-S biotype was substituted by Ser in Lz-R biotype in Domain A of ALS.
► Pro-197-Ser mutation endow Lz- R biotype with highly resistance to tribenuron.
► Tribenuron resistance in C.bursa-pastoris is elucidated for the first time.