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Glufosinate is an important and widely used non-selective herbicide active on a wide range of plant species. Evolution of resistance to glufosinate in weedy plant species (including the global weed Eleusine indica) is underway. Here, we established the molecular basis of target site glufosinate resistance in Eleusine indica. Full-length E. indica glutamine synthetase (GS) iso-genes (EiGS1-1 , 1-2 , 1-3 , and EiGS2) were cloned, and expression of EiGS1-1 and EiGS1-2 was higher than that of EiGS2. A novel point mutation resulting in a Ser59Gly substitution in EiGS1-1 was identified in glufosinate-resistant plants. Rice calli and seedlings transformed with the mutant EiGS1-1 gene were resistant to glufosinate. Purified mutant EiGS1-1 expressed in yeast was more tolerant to glufosinate than the wild-type variant. These transgenic results correlate with a more glufosinate-resistant GS in the crude tissue extract of resistant versus susceptible E. indica plants. Structural modelling of the mutant EiGS1-1 revealed that Ser59 is not directly involved in glufosinate binding but is in contact with some important binding residues (e.g. Glu297) and especially with Asp56 that forms an intratoroidal contact interface. Importantly, the same Ser59Gly mutation was also found in geographically isolated glufosinate-resistant populations from Malaysia and China, suggesting parallel evolution of this resistance mutation. [ABSTRACT FROM AUTHOR]

BACKGROUND: Relatively new herbicides that target 4‐hydroxyphenylpyruvate dioxygenase (HPPD) are now available for use on the world's great grain crops (rice, wheat, corn and soybean) and for other uses. With widespread and persistent use of HPPD‐inhibiting herbicides, the evolution of HPPD‐inhibiting herbicide resistant weeds is inevitable. Currently, resistance to HPPD‐inhibiting herbicides is known in two weed species, waterhemp and Palmer amaranth. Here, we report a HPPD‐inhibiting herbicide resistant wild radish population from the Western Australia grain belt. This population was not selected with HPPD‐inhibiting herbicides, rather it evolved resistance to earlier used herbicides with different modes of action and exhibits cross‐resistance to HPPD‐inhibiting herbicides. RESULTS: Dose–response experiments showed the resistant (R) population exhibits 4 to 6.5‐fold resistance to the HPPD‐inhibiting herbicides mesotrione, tembotrione and isoxaflutole, compared to the susceptible (S) population. This resistance is not target‐site based as cloning of full coding sequences of the HPPD genes from S and R plants did not reveal resistance‐endowing single nucleotide polymorphisms. The HPPD gene expression levels are similar in S and R plants. In addition, no differences in [14C]‐mesotrione uptake and translocation were observed in the S and R plants. However, the time required for R plants to metabolise 50% [14C]‐mesotrione is 7.7‐fold faster than for the S plants. CONCLUSION: We confirm resistance to HPPD‐inhibiting herbicides exists in a population of the economically damaging global weed wild radish. The resistance in this population is due to a non‐target‐site based enhanced rate of herbicide metabolism. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The article presents a discussion on glyphosate-resistant weeds. Glyphosate is a herbicide used around the world to control weeds since 1996. With the increase in the planting of glyphosate-resistant crops in the U. S. came the growth of glyphosate-resistant weeds including Ambrosia artemissifolia L. and Amaranthus palmeri S Watson. Glyphosate-resistant weeds were also found in Argentina and Brazil. The article mentions that glyphosate-resistant weeds are expected to evolve with continued planting of glyphosate-resistant crops. It also discusses the importance of diversifying weed management for the continued use of glyphosate as herbicide.

This article reports on glyphosate, a highly effective broad-spectrum herbicide. It discusses that glyphosate has become the dominant herbicide worldwide because it is very toxicologically and environmentally safe. Glyphosate is the only herbicide that targets 5-enolpyruvyl-shikimate-3-phosphate synthase and it translocates well. Its cost has dropped dramatically after glyphosate became a generic compound. However, the use of this herbicide is being threatened by the evolution of glyphosate-resistant weeds.

In Australian grain-growing regions, the evolution of weeds resistant to multiple herbicides threatens the sustainability of existing cropping systems. As a result, herbicide susceptibility is considered to be a potentially exhaustible resource. Based on a survey of 132 Western Australian grain growers, perceptions of various factors relating to the herbicide resource were measured. These include the rate of resistance evolution, cost of resistance, the future availability of replacement herbicides, reductions in the level of resistance in a population over time, and mobility of resistance. Growers were found to have a generally high level of awareness of herbicide resistance and consider it to have a high potential cost. However, many perceive that the stock of effective herbicides is likely to be renewed in the short term, either through new herbicide development or resistance reversion. Potential opportunities for targeted extension to improve farmer decision-making are identified. [Copyright &y& Elsevier]

The RIM (resistance and integrated management) model is presented. RIM represents a wide diversity of herbicide and non-herbicide options for management of Australia''s most important crop weed, Lolium rigidum, in the context of the non-irrigated extensive farming system of southern Australia. Enterprise choices in the model include cereals, lupins, canola and three types of pastures for grazing by sheep. Users of RIM may specify the enterprise sequence and any feasible combination of the 35 weed treatment options each year over 10 or 20 years. Weed treatment options include selective herbicides (11), non-selective herbicides (5), non-chemical treatments (16) and user-defined treatments (3). The model represents weed and seed bank population dynamics, weed-crop competition, weed treatment impacts (including phytotoxicity), agronomic details, and financial details. Economic and biological model results are presented for scenarios with differing levels of availability of selective herbicides and different rotational sequences. [Copyright &y& Elsevier]