BACKGROUND Glyphosate has been used for weed control in South China in various situations for four decades, and most Eleusine indica populations are suspected to have evolved resistance to glyphosate. This research investigated underling target‐site glyphosate resistance mechanisms in six field‐collected, putative glyphosate‐resistant (R) E. indica populations. RESULTS The six R E. indica populations were confirmed to be low (1.8 to 2.6‐fold) to moderately (5.6‐ to 8.4‐fold) resistant to glyphosate relative to the susceptible (S) population. Sixty‐seven glyphosate‐surviving plants from the six R populations were used to examine target‐site resistance mechanisms. Target‐site 5‐enolpyruvylshikimate3‐phosphate synthase (EPSPS) overexpression (OE) (plus further induction by glyphosate treatment) and gene copy number variation (CNV) occurred in 94% R plants, and among them, 16% had the P106A mutation and 49% had the heterozygous double TIPS (T102I + P106S) mutation (plus P381L). In addition, a low number of R plants (6%) only had the homologous TIPS (plus P381L) mutation. The (CT)6 insertion mutation in the EPSPS 5†‐UTR always associates with EPSPS OE and CNV. Progeny plants possessing EPSPS OE/CNV (and P106A) displayed low level (up to 4.5‐fold) glyphosate resistance. In contrast, plants homozygous for the TIPS mutation displayed higher (25‐fold) resistance to glyphosate and followed by plants heterozygous for this mutation plus EPSPS OE/CNV (12‐fold). CONCLUSIONS Target‐site glyphosate resistance in E. indica populations from South China is common with prevalence of EPSPS OE/induction/CNV conferring low level resistance. Individual plants acquiring both the TIPS mutation and EPSPS OE/CNV are favored due to evolutionary advantages. The role of (CT)6 insertion mutation in EPSPS CNV is worth further investigation. © 2021 Society of Chemical Industry.
In order to determine the susceptibility of Ipomoea cairica to herbivory, the compensatory growth and photosynthetic characteristics of I. cairica plants were measured after simulated herbivory by leaf trimming in three patterns: leaf‐apex removal, leaf‐edge removal, and perforation. The leaf‐edge removal resulted in a significantly reduced total biomass and root biomass of the plants, but the leaf‐apex removal and perforation had no significant influence on the plant growth. The defoliation patterns had significant effects on the photosynthesis of I. cairica. The net photosynthetic rate and stomatal conductance of the plants whose leaf edges had been removed were the highest among the three defoliation patterns and the fraction of absorbed light that is used in Photosystem II photochemistry increased greatly, while the fraction of light energy that is dissipated thermally decreased. The increased photosynthetic rate as a result of the leaf‐edge removal treatment could be attributed to a decrease in stomatal limitation and an increase in the Rubisco content, as well as higher photosynthetic efficiency and less light energy being dissipated as heat. Increased photosynthesis in the plants whose leaf edges had been removed changed the carbon allocation and resulted in less root development. As the expansion of I. cairica primarily depends on clonal growth, smaller roots could limit its uptake of nutrients from the soil. These direct and indirect effects indicate that leaf‐edge‐feeding herbivores could have potential in the biological control of I. cairica.
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