psbA mutation (Ala251 to Val) in Chenopodium album resistant to triazinones

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Weed Resistance to Herbicides

Unfortunately, herbicide resistance developed shortly after the introduction of the herbicides 2,4‐D in 1957. According the herbicide resistance mechanisms, all processes can be grouped as follows: target‐site resistance, non‐target‐site resistance, cross‐resistance and multiple‐resistance. Target‐site resistance is generally due to a single or several mutations in the gene encoding the herbicide‐target enzyme, which, in turn, decreases the affinity for herbicide binding to that enzyme. Non‐target‐site resistance is caused by mechanisms that reduce the amount of herbicidal active compound before it can attack the plant through the reduced absorption or altered translocation, increased herbicide sequestration or enhanced herbicide metabolism. Cross‐resistance means that a single‐resistance mechanism causes resistance to several herbicides with some mode of action. Multiple‐resistance is a situation where two or more resistance mechanisms are present within the same plant, often due to sequential selection by herbicides with different modes of action. Currently, herbicide resistance has been reported in 478 weed biotypes (252 weed species) in 67 countries. Many of those biotypes are resistant to acetolactate synthase (ALS) inhibitors, PS II inhibitors, ACC‐ase inhibitors and EPSPS inhibitors. Strategy for herbicide‐resistance weed management must involve all the available preventive, cultural, mechanical and chemical measures for effective, safe and cost‐effective weed control

Rice breeding in the new era: Comparison of useful agronomic traits

Understanding agronomic traits at a genetic level enables the leveraging of this knowledge to produce crops that are more productive and resilient, have better quality and are adjusted for consumer preferences. In the last decade, rice has become a model to validate the function of specific genes, resulting in valuable but scattered information. Here, we aimed to identify particular genes in rice related to traits that can be targeted by different mutation techniques in the breeding of crops. We selected gain of function, misfunction, and specific mutations associated with phenotypes of agronomic interest. The review includes specific trait-related genes involved in domestication, stress, herbicide tolerance, pathogen resistance, grain number/quality/weight, plant structure, nitrogen use, and others. The information presented can be used for rice, other cereals, and orphan crops to achieve a superior and sustainable production in challenging farming conditions

Herbicide Resistance in Phalaris Species: A Review

Weeds, such as Phalaris spp., can drastically reduce the yield of crops, and the evolution of resistance to herbicides has further exacerbated this issue. Thus far, 23 cases of herbicide resistance in 11 countries have been reported in Phalaris spp., including Phalaris minor Retz., Phalaris paradoxa L., and Phalaris brachystachys L., for photosystem II (PS-II), acetyl-CoA carboxylase (ACCase), and acetolactate synthase (ALS)-inhibiting herbicides. This paper will first review the cases of herbicide resistance reported in P. minor, P. paradoxa, and P. brachystachys. Then, the mechanisms of resistance in Phalaris spp. are discussed in detail. Finally, the fitness cost of herbicide resistance and the literature on the management of herbicide-resistant weeds from these species are reviewed

Differential sensitivity of Atriplex patula and Chenopodium album to sugar beet herbicides : a possible cause for the upsurge of A. patula in sugar beet fields

In the last decade, the prevalence of Atriplex patula as a weed in the Belgian sugar beet area has increased. Possible reasons for its expansion in sugar beet fields, besides a poor implementation of the low-dose phenmedipham/activator/soil-acting herbicide (FAR) system, might be low sensitivity or evolved resistance to one or more herbicides used in sugar beet. Dose-response pot bioassays were conducted in the glasshouse to evaluate the effectiveness of five foliar-applied sugar beet herbicides (metamitron, phenmedipham, desmedipham, ethofumesate and triallate) and three pre-plant-incorporated herbicides (metamitron, lenacil, dimethenamid-P) for controlling five Belgian A.patula populations. Local metamitron-susceptible and metamitron-resistant populations of Chenopodium album were used as reference populations. Effective dosages and resistance indices were calculated. DNA sequence analysis of the photosystem II psbA gene was performed on putative resistant A.patula populations. Overall, A.patula exhibited large intraspecific variation in herbicide sensitivity. In general, A.patula populations were less susceptible to phenmedipham, desmedipham, ethofumesate and triallate relative to C.album populations. Two A.patula populations bear the leucine-218 to valine mutation on the chloroplast psbA gene conferring low level to high level cross-resistance to the photosystem II inhibitors phenmedipham, desmedipham, metamitron and lenacil. In order to avoid insufficient A.patula control and further spread, seedlings should preferentially be treated with FAR mixtures containing higher-than-standard doses of metamitron and phenmedipham/desmedipham and no later than the cotyledon stage

A Bioassay to Determine Poa annua Responses to Indaziflam

Herbicide resistance within Poa annua is widespread in managed turfgrass systems. In 2020, a P. annua collection from a golf course in the southeastern United States was reported to be resistant to indaziflam as well as six other mode-of-action groups. Considering P. annua is the most troublesome weed in turfgrass, a bioassay to screen other collections with putative indaziflam resistance is needed. A dose-response experiment was conducted with ten concentrations of indaziflam (0, 250, 500, 750, 1000, 1250, 1500, 2000, 4500, and 9000 pM) in Gelrite® culture during 2021 and 2022. An herbicide-susceptible (S1) collection of P. annua, a resistant standard (Site 3A), and a collection with putative-resistance to indaziflam (Site 18) were included in this experiment. Petri dishes were filled with 80 mL of Gelrite®(3.75 g/L) containing technical grade (≥ 98%) indaziflam (Sigma-Aldrich, St. Louis, MO) and rifampicin (1000 ppm). Each plate was sealed with parafilm after placing 15 seeds of a single collection on the Gelrite®surface. During the experiment, all plates were placed at a 75-degree angle to facilitate gravitropic root growth and stored in a growth chamber set to a constant air temperature of 16 °C. At 14 days after seeding (DAS), the length of root tissue (mm) protruding from each seed was recorded with digital calipers. Root length data from each P. annua collection were expressed as a percentage of the non-treated and subjected to non-linear regression analysis to calculate indaziflam concentrations required to reduce root growth by 70% (EC70). Statistically significant differences were detected among P. annua collections with the EC70 for the herbicide-susceptible collection measuring 742 pM [95% confidence interval (CI) = 686 to 803 pM] compared to 2226 pM (CI = 1851 to 2759 pM) for Site 3A and 4263 pM (CI = 3471 to 5382) for Site 18. Overall, these findings indicate that a discriminatory dose of 750 pM can be used to differentiate among susceptible and resistant individuals when screening additional P. annua collections from field sites where poor control is observed following broadcast applications of indaziflam

Improving Metribuzin Tolerance in Lentil (Lens culinaris)

Weeds are a major limitation to lentil (Lens culinaris Medik.) production worldwide with grain yield losses of up to 87% from weed competition. In broad-acre mechanized lentil production systems, weed control relies on herbicide application; however, limited options exist. This study identified, characterised and validated novel tolerance in lentil to the photosystem II (PSII) inhibitor herbicide, metribuzin. Field research involving variable sowing dates, induced shade treatments and metribuzin rate were conducted to understand soil and weather factors responsible for herbicide phytotoxicity in lentil. Analysis of soil and weather factors around the time of herbicide application to the cultivar PBA Flash suggested a combination of factors were involved. Heavy rainfall within 10 days of application, particularly on light textured soils or where soil moisture was low, was most strongly linked to plant damage. A higher level of selective tolerance to metribuzin than that currently present in commercial lentil cultivars is required. Two methods, germplasm screening using a hydroponic sand assay and field screening of a large mutated population of PBA Flash, were used to identify lines with improved tolerance to metribuzin compared to current cultivars. Dose response experiments found germplasm line SP1333 had GR50 (the rate required to reduce dry weight (DW) 50%) values up to four-fold that of PBA Flash. However, GR50 values were greater than 25-fold that of PBA Flash in mutant selections M009 and M043. A field study in Canada with 20 Canadian and Australian genotypes confirmed the improved tolerance level of the mutants. Dose response analysis of five PSII inhibiting herbicides and DNA sequencing of the psbA chloroplast gene was undertaken to quantify the spectrum and mechanism of herbicide tolerance in M009 and M043. Compared to PBA Flash, metribuzin tolerance was increased 33-fold in M043 and 10-fold in M009, but no additional tolerance to other herbicides. Nucleotide sequencing of the psbA gene of both mutants identified a substitution at position 751 compared to PBA Flash. The resulting deduced amino acid sequence indicated an Ala251Thr substitution as responsible for the metribuzin tolerance. The substitution is unique in mutagenised higher plants and is the first report of an induced psbA target site mutation in higher plants. Reciprocal F1, F2 and F3 populations developed from M009 and M043 with PBA Flash identified a maternal inheritance pattern, but with paternal leakage in approximately 20% of F1 phenotypes. Reciprocal BC1F2 and BC1F3 populations were developed to identify any fitness cost associated with the tolerance. Field experiments identified reductions in net assimilation rate, DW and grain yield (GY) in tolerant lines with a fitness cost of 20 to 40%. This finding is comparable with the fitness cost measured in triazine tolerant (TT) canola due to tolerance to the PSII inhibiting triazine herbicides. Agronomic field experiments over two years at contrasting sites in South Australia compared the plant growth and GY of M009 and M043 with PBA Flash and SP1333 to post-emergent metribuzin. Clear differences existed in the responses of M009 and M043 compared with PBA Flash and SP1333 to metribuzin rate across sites. This finding confirmed that the mutant genotypes have an agronomically useful level of tolerance to metribuzin in southern Australia. However, DW was generally reduced linearly with metribuzin rate in both M043 and M009 suggesting a level of herbicide sensitivity at higher rates on some soil types. All three lentil genotypes with improved metribuzin tolerance are in use as parents in Australian breeding programs. The higher level of tolerance and superior agronomic performance of M043 makes it the genotype of choice. Knowledge of the genetic controls of inheritance and associated fitness cost of the target site provided by this study will aid plant breeders in rapid and effective incorporation of the tolerance into agronomically accepted plant types. The potential of developing a metribuzin tolerant lentil industry in Australia, similar to that which has occurred in TT canola, now exists.Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 201

Weed control in sugar beet without the active substances desmedipham and phenmedipham

Desmedipham und Phenmedipham sind seit vielen Jahren bewährte und wichtige herbizide Wirkstoffe im Zuckerrübenanbau. Im Rahmen der regulären Wirkstofferneuerung wurde für Desmedipham entschieden, die Genehmigung als Wirkstoff in Pflanzenschutzmitteln nicht zu erneuern. Für Phenmedipham ist das Ergebnis der Bewertung zum gegenwärtigen Zeitpunkt offen. Um die Wirksamkeit von Herbizidapplikationen ohne Desmedipham und Phenmedipham zu prüfen, wurden in den Jahren 2018 und 2019 Feldversuche an insgesamt 22 Standorten in Deutschland durchgeführt. Dabei wurden vier Versuchsglieder zweijährig und acht weitere einjährig geprüft. Die Ergebnisse zeigen in beiden Jahren, dass ohne Desmedipham und Phenmedipham Wirkungslücken bei der Bekämpfung von Weißem Gänsefuß (Chenopodium album) und Windenknöterich (Polygonum convolvulus) entstehen können. Weitere zugelassene Produkte mit blattaktiven Wirkstoffen in der Tankmischung konnten diese Lücke nicht vollständig kompensieren. Zudem ist ohne Desmedipham und Phenmedipham von einem zunehmenden Risiko für die Entstehung von metamitronresistenten Biotypen des Weißen Gänsefußes auszugehen. Zur Beurteilung der herbiziden Wirkung gegenüber anderen in Zuckerrüben bedeutenden Unkrautarten sind weitere Versuche erforderlich.Desmedipham and phenmedipham are proven and important herbicides in sugar beet cultivation since many years. The regular renewal of active ingredients was not approved for desmedipham as an active ingredient in crop protection products. For phenmedipham, the result of the renewal is currently open. To determine the efficacy of herbicide applications without desmedipham and phenmedipham, field trials were conducted in 2018 and 2019 at a total of 22 sites in Germany. Four treatments were tested in both years and eight others in one year. The results showed in both years that gaps in the control of fat hen (Chenopodium album) and black bindweed (Polygonum convolvulus) can arise without desmedipham and phenmedipham. Other authorized foliar active ingredients in the tank mix were unable to fully compensate for this gap. Moreover, without these two active ingredients there is an increased risk for the development of metamitron-resistent biotypes of fat hen. Further trials are required to evaluate the herbicidal efficacy against others weeds in sugar beet