Abstract:
Six Conyza bonariensis (L.) Cronquist populations were screened in a pot experiment at the
University of Pretoria’s Hatfield experimental farm to evaluate and confirm the degree of glyphosate
response. Resistance factors ranged from 2.7- to 24.8-fold compared to the most susceptible biotype.
Partial sequencing of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene found no mutation
at the Thr102, Ala103 or Pro106 positions. EPSPS mRNA expression levels in glyphosate-resistant
biotypes (Swellendam and Piketberg seed sampling sites) were comparable or lower than those in
susceptible biotypes (George and Fauresmith sites). Additionally, the highest expression level was
reported in the susceptible Fauresmith biotype. These results indicate that glyphosate resistance in
the tested resistant biotypes is not caused by target-site mutations and EPSPS gene amplification.
Leaf surface characteristics can influence the spread and subsequent absorption of glyphosate. The
study established non-significant results in the amount of leaf wax and insufficient mean separations
in cuticle thickness and trichome density data. Therefore, the observed differences in response
of biotypes to glyphosate treatment could not be attributed conclusively to differences in the leaf
morphological characteristics investigated. Results from the inheritance study were consistent with
glyphosate resistance being inherited in an incompletely dominant manner when plants were treated
with glyphosate herbicide at 900 g ae ha−1
.
Description:
SUPPLEMENTARY MATERIAL : FIGURE S1. Transmission electron micrographs
of outer epidermis cell wall of C. bonariensis showing cuticular membrane. FIGURE S2. Transmission
electron micrographs of outer epidermis cell wall of C. bonariensis showing cuticular undulations.
FIGURE S3. Scanning electron micrographs of C. bonariensis trichomes on leaf surface (A and B) and
on cross section of leaf (C) showing trichomes on both adaxial and abaxial sides. FIGURE S4. Light
microscope images of C. bonariensis leaf surface showing numerous trichomes on the adaxial (‘A’)
and fewer trichomes on the abaxial (‘B’) leaf surfaces. Figure S5. Melting curves for the EPSPS and
Actin genes of C. bonariensis. TABLE S1. qRT-PCR primer sets used in the study.